Handheld receiver blocking shootout

Ever since my outing on to Ling Fell yesterday I have been bugged by not knowing for sure whether the problems I experienced with the VX-8GR were really caused by receiver overload or blocking. I like the construction and features of the Yaesu. But a radio that makes you miss some of the contacts you have laboriously sweated up a summit to make is about as much use as a chocolate teapot. I wondered if I could devise a test to give me an idea of the relative strengths of the different 2m radios. I did, and the candidates are lined up in order of merit below, the worst on the left and the best on the right.

The test methodology was crude. I connected each radio to my dual band vertical and tuned in a weakish station: the GB3AS repeater on 145.600MHz, which is normally an S3 signal - fully readable but with some background noise on the audio. I then transmitted a carrier on 144.025MHz using another radio on a helical antenna a few metres from the vertical. I tried two power levels of the interfering signal, 3.5W ("high power") and 0.5W ("low power"), these being the available power levels of the test radio. This 8dB difference in the interfering signal level had different effects on the ability to receive the repeater signal.

I am well aware of the limitations of the test I carried out. In real life SOTA or WOTA use a radio may be subjected to strong in-band signals from activators on other summits but they will not be as strong as the signal from a radio a few metres away from the antenna. A radio is likely to be subjected to strong signals from outside the amateur band such as pagers and other commercial signals, which the bandpass filters in modern radios due to the marketing-driven necessity of providing wideband receive coverage will do nothing to attenuate. Many strong signals may mix together to cause intermodulation effects if not blocking. However, a receiver that can handle a strong in-band interfering signal is likely also to be better at coping with many strong signals being received over a range of frequencies. So I think my test results have some validity.

Beginning with the worst receiver, the results are as follows.

• VX-8GR. This receiver was the worst affected by blocking. Noticeable desensing of the repeater signal occurred when the in-band carrier was on low power, while a weak noisy "4 by 1" signal was killed completely. The repeater signal cut out completely when the in-band carrier was keyed on high power. Engaging the RX ATT (menu option 1) caused the repeater signal to drop below the squelch threshold so it was not much help though it did reduce the desensing effect on stronger signals.
• JMT-228. The VX-8 was slightly worse than the Jin Ma Tong JT-228, a £30 Chinese handheld bought on eBay. In fairness, the JT-228 is slightly less sensitive than the Japanese ham radios (judging by the signal to noise ratio on weak signals) which may have helped it a bit. Desensing was noticed when the in-band carrier was on low power, and the repeater signal cut out when it was on high power.
• TH-D72. The Kenwood TH-D72 may only be third worst (or third best) but in fact it was a whole lot better. No detectable desensing occurred when the in-band carrier was on low power. Some desensing occurred, in the form of a drop in S-meter reading and increased noise on the audio, when the carrier was on high power.
• GP-300. Excellent performance was given by the Motorola GP-300. No desensing was noticed when the in-band carrier was on low power. There was a very slight but hardly noticeable increase in background noise level when the carrier was keyed on high power.
• TH-205E. I bought this old boat anchor as a "spares or repair" radio for £6 on eBay for the fun of seeing if I could get it going. With the high capacity battery pack it is about the weight and bulk of an FT-817 and not something I would particularly want to haul up a summit. But no desensing of the repeater signal was observed even when the in-band carrier was keyed on high power, making this the best performing receiver of all.

Out of interest I also carried out the test on my FT-817ND and the Kenwood TM-D710 I use as my 2m base station. The FT-817ND was slightly better than the TH-D72: there was no effect with the low power carrier but the high power one brought a noticeable background hiss on the signal. The TM-D710 performed close to the TH-205E. There was barely any noticeable effect from the high power in-band carrier.

I think the results of these tests, crude though they are, are interesting. The bigger the radio, the more likely it is to have a receiver able to handle adjacent strong signals. Paying lots of money for the latest technology is no guarantee of getting a better receiver. In fact, just the opposite. An ex-commercial handheld or a ham band one from the days when wide band receive coverage was not considered important will work better than the latest marvels.

Were it not that I find the full APRS functionality of the VX-8GR and TH-D72 useful, I'd be tempted to sell both those radios and just use a dumb tracker plugged into the mic socket of one of the others tuned to 144.800. Either I use the VX-8GR for APRS only and carry another radio for making contacts or I must try harder to love the TH-D72. Decisions, decisions. But at least I now have a bit more information to base them on.

VX-8GR receiver overload

This afternoon I went for a stroll up Ling Fell, LDW-205. It was a fine afternoon and I wanted a bit of exercise. I took the VX-8GR so I could test the new QRU feature of Lynn KJ4ERJ's APRSISCE/32 software that allows an APRS user to receive information about nearby objects on request. I have created a QRU server for Wainwright summits so that an APRS user in the fells could receive information about the nearest summits, to aid identification or navigation.

I put a 2m helical antenna on the rucksack support for the walk up, so the VX-8GR could send my position. The other channel was monitoring 145.500MHz (S20) the FM calling channel. As I gained height I started to hear some loud bursts of interference, a combination of a whine and a buzz, on S20. When I got to the top I switched antennas to the RH-770 dual band telescopic. My first call was answered by Colin, 2E0XSD. His signal was moving the meter on the VX-8GR to an S3 or 4 but there was intermittently a lot of crackly interference over his audio. I tried engaging the RX Attenuator option in the VX-8GR menu and it did seem to improve things a bit, but not completely.

A bit later, when I was testing the QRU server, I could hear the APRS packets coming back from my gateway (which is line of sight from Ling Fell, just behind me in the distance in the picture) but they sounded distorted and the VX-8GR didn't decode them.

I wondered if there was a fault with the cable to the rucksack mount so I put the antenna directly on the radio. My next call was answered by Geoff G4WHA from his car in the car park in Penrith. He was 5 by 1 but his signal was cutting out intermittently. I got the feeling the problem wasn't Geoff's, but was my receiver cutting out due to overload from some nearby transmitter. There is a commercial mast a couple of miles away on the other side of the valley, though I have no idea what is on it.

I am starting to get a feeling that the receiver in the VX-8GR is not much good on summits when connected to a decent antenna. I first noticed odd things with the original VX-8R I had when I tried it out with a SOTA Beams MFD. There have also been several occasions when other people using VX-8 series rigs on summits have failed to hear me, even though I could hear them clearly and in some cases was running much more power than they were. This is quite disappointing. I really like the VX-8GR and much prefer it over the Kenwood TH-D72 which I have been thinking about selling. But perhaps it would be better to keep the Kenwood.

I wish that I had the test equipment to try to compare the strong signal performance of my various hand held radios. HF radios have their receiver performance exhaustively tested and the results of tests by the likes of Sherwood Labs are endlessly debated on various reflectors despite the fact that the only difference it is likely to make is whether you can copy a very weak station right next door to an extremely strong one. But the reviews of VHF radios focus only on matters like the ease of use of the menu system, how many memories it has or how the scanning works.

I think the receive performance of VHF/UHF hand helds is just as important as for HF receivers. If a receiver can't cope on a hilltop on the middle of nowhere how will it fare with the signal levels in a busy urban environment? Heck, you might be missing vital emcomms messages and not know it! It's about time the ham radio magazines started publishing blocking dynamic range and cross-mod figures for hand held radios.

Coffee and cakes on Latrigg

For Easter Sunday, Bassenthwaite Rotary Club of which fellow WOTA enthusiast Phil M0AYB is a member put on, in aid of charity, a Felltop Café on the summit of Latrigg, a very minor but frequently visited Wainwright summit just to the north of Keswick. Phil planned to activate the summit while he was there. The opportunity to have coffee and cakes while activating a summit was too good to resist so I decided to pay Phil a visit and do my own activation. The weather played fair and was glorious, too.

Latrigg is an easy summit - really a foothill of Skiddaw - and so it was not too much of a problem for my back which is better but still not fully recovered. The views on the way up are glorious, which is why Latrigg is a popular target for visitors to the area.

From the summit you look down to the town of Keswick, with its lake, Derwentwater, beyond.

Soon after we arrived I heard Richard G1JTD/P on Yoke in the Eastern Fells, and worked him for a summit to summit. Yoke was not a summit I'd have much hope of working from home so that was a bonus.

Olga and I went and got some coffee and Cumberland sausages in a bap from the café. The coffee was excellent. There was quite a queue for refreshments and I hope the enterprise made a lot of money for Bassenthwaite Rotary Club's charity.

Phil had brought up a 9 element Tonna on a short mast which he was using with an FT-817 running 2.5W. I was using the Nagoya NA-767 mentioned in my previous post on comparing handheld antennas with the Kenwood TH-D72 and 5W output (though not in the picture.) I worked most of the same stations Phil had, and some of them commented that my signal was similar or close to as strong as Phil's, which was quite gratifying.

This was the first activation I have done with the TH-D72. I have been hoping that in time I would grow to like this radio but I'm afraid it has not won me over. It's too big and bulky and the case feels plasticky and not rugged enough to stand the knocks and bumps experienced on a summit. I still prefer the VX-8GR, though as noted in previous posts the receiver of that gets easily de-sensed in the presence of the strong signals experienced on a hilltop with a good antenna.

Chirp, chirp

I discovered some free radio memory management software this morning. Called CHIRP, which is presumably an acronym that ends with "Radio Programming", it is a free, cross-platform, cross-radio programming tool that is being developed by Dan Smith, KK7DS. CHIRP works on Windows and Linux (and MacOSX with a little work, according to Dan). It supports a whole list of radios from manufacturers such as Alinco, Icom, Kenwood, Yaesu and Wouxun.

As the VX-8R is listed, I thought I'd give it a try with my VX-8GR. Unlike the excellent but non-free FTBVX8 software from G4HFQ, CHIRP doesn't prompt you with the steps you need to perform on the radio. If you just connect the radio, load the software and start the download nothing will happen. With the VX-8R you must begin with the radio turned off, then after starting the download press and hold the F/W button on the side while turning the radio on. When CLONE appears on the display, press BAND. The download will then start and the program will display its progress. With other radios different steps will no doubt be needed. Hopefully at some point prompts will be incorporated into the software.

My first download attempt did not complete. Instead an error message appeared near the end. But I tried again. This time the memories were downloaded successfully and displayed in the program as you can see. The "cross-radio" part of the specification means, presumably, that memories are saved in a unified format so you can download them from one radio and upload them to a different one.

I didn't try uploading to the radio. I have heard of people bricking radios by using software that wrote unexpected stuff and I'd already seen one error message. Besides, I have the FTBVX8 software and I didn't have any changes I wanted to make anyway. But if you don't want to pay for memory management software, you want to maintain one memory file and upload it to multiple different radios or you want a program that will run on Linux or Mac OS, CHIRP is a development that's worth keeping an eye on.

Two more northern fells

Yesterday I was out hiking round the back of Skiddaw in Wainwright's Northern Fells to activate Great Sca Fell (LDW-114) and Brae Fell (LDW-134). One reason for being out and about in that area was that Phil G4OBK was planning to activate Great Calva (LDW-095) which is one of the three summits I need to complete the Northern Fells as a chaser. I'd have been less keen if the weather had been miserable, but Thursday was a glorious day, sunny but not too hot and without the breeze that can often make it icy cold on the tops even when it is warm in the valleys.

It is a long, steady plod up from Longlands and I reached the summit of Great Sca Fell around 12:30. I put up the WOTA Pole and then sat down to eat my lunch. To raise the height of the antenna I used my walking pole for the bottom section. This didn't give me as much extra height as I'd hoped as the inner sections of the telescopic pole slid up inside the PVC tubing so I had to collapse it and just use the thickest, topmost section.

I connected the VX-8GR to the antenna to beacon my position on APRS while I ate the lunch Olga had made me. I tuned around whilst I was eating and heard a couple of distant stations. I observed their signals being desensitized intermittently. Clearly the VX-8GR receiver is not up to being connected to a good antenna in a good location.

After lunch I connected the Motorola GP300 - which has a much more robust receiver - to the antenna and began calling CQ WOTA. I worked 11 stations in all from Great Sca Fell, but they were all from the northen area as signals to the south were blocked by the great bulk of Skiddaw and Blencathra. I waited for Phil G4OBK to arrive on his first summit of the day, Bakestall, so we could have a summit-to-summit contact. I then called upon Mark MM1MPB and Colin 2E0XSD to help with my second objective of the day, which was to do some tests to see how much difference the WOTA Pole made to my signal compared to other antennas.

First I compared the signal between the WOTA Pole (which is a Slim Jim made of 300 ohm ribbon cable inside some PVC electrical conduit) and the 5/8 wave telescopic Black Whip antenna from jeepbangkok on eBay. I'd been pretty impressed with the 5/8 telescopic on previous activations but the reports from Mark and Colin suggested that the WOTA Pole was a couple of S-points better.

Unfortunately while extending the telescopic antenna to make the test I broke it! That's the end of that, which is a pity because I'm sure there will be circumstances - such as on busy summits or rocky ones where there is no earth to drive the guy pegs in - where the telescopic would still be useful.

For an additional test I tried an 8 inch long single band helical "rubber duck" which I'd previously established to be comparable to a quarter wave whip and a noticeable improvement over the stock dual band antenna that comes with Japanese handhelds. Colin couldn't hear me on the helical at all, while Mark's verdict on my signal was "awful." So the WOTA Pole is very definitely worth the trouble of erecting it and enables me to give points to stations that would not otherwise be able to hear me.

I packed everything up and made my way over to Brae Fell which was half way back to the car by another route. I set up the antenna and finished the rest of my coffee. A lone skylark, perhaps the first of the year, circled calling overhead. I began calling on the radio. Again there were plenty of takers. I worked 12 stations in all including another summit to summit with G4OBK/P on Great Calva.

So a successful day out (apart from breaking an antenna.) I just need to work someone on Mungrisdale Common and Souther Fell to complete the Northern Fells. They have been activated before: unfortunately they are not workable from home due to being of only moderate height and on the other side of Skiddaw. As they are probably the two most boring hills in the entire Lake District they are not often visited so I may have a bit of a wait until I can claim my Wainwrights On The Air Northern Fells chaser certificate.

Boosting the VX-8GR on APRS

A few weeks ago I did an analysis of the audio levels of different APRS radios and lamented the low level of the audio transmitted by the Yaesu VX-8GR. An Italian ham wrote to me enclosing a copy of a document he obtained from Yaesu showing how to increase the transmit deviation. I decided to give it a try. You can find a copy of this document in the Files section of the VX-8R Yahoo group, but I will describe the process here.

Note that performing this adjustment will increase the transmit deviation on speech as well. There is no way to increase the packet deviation independently. Note too that while you are in the alignment menu it is possible to change other settings as well by accident. This may be undesirable, especially if you don't have the test equipment to realign the radio properly, so be careful and perform the adjustment at your own risk! Finally, note that these instructions will work only for the VX-8GR. There are instructions for accessing the alignment menu of the VX-8R on the web. They don't work for the GR and these instructions don't work for the R. I have no idea if any of the instructions work with the DR.

To avoid entering the alignment menu accidentally, Yaesu has made accessing it quite difficult. First you must enable the CW ID (main menu item 16) and program a password AH041M into it. The manual explains how to do this. You must then set the transceiver to single band mode on the A band, in VFO mode (not memory) on a frequency of 430.000MHz. Now switch the radio off.

Press and hold the HM/RV key and turn the VX-8GR back on. If all the above steps were carried out correctly the radio should start up in alignment mode showing the first alignment setting. Rotate the control knob clockwise a few clicks to select the MAX DEV adjustment, then press the V/M button to select it. A pointer symbol should appear to show that adjustment is selected.

The control knob now adjusts the deviation setting. Make a note of the original value in case you want to reset it, then turn it up to 254. Yes, I know this sounds like a CB "screwdrivers to the max" tweak but as you can see from the spectrograms below, even at that setting the packet deviation won't quite match that of the Kenwood rigs. Press the V/M button again to exit the adjustment, then press HM/RV to exit the alignment menu. The radio will restart in normal operational mode. Don't forget to clear the CW ID once you're happy with the new setting.

The spectrograms below show the difference made by the adjustment, with the Kenwood TH-D72 shown as a reference.

 

As you can see, the peak deviation of the high tone is now within 1dB of that of the Kenwood, though the Yaesu still has more low-frequency roll-off. Nevertheless, this is as good as it gets with the Yaesu. If you still can't hit the digis you think you ought to, perhaps you'd be better off with a Kenwood.

As I said earlier, this deviation adjustment makes your audio louder as well. You, your local hams or your local repeaters might not like this. The VX-8GR has a "Half Deviation" menu option which will reduce the deviation back to approximately what it was before this adjustment, but it works across the whole radio and not per band, so you can't have the wider deviation only on the APRS band.

It is interesting to note that in the Yaesu alignment document the deviation alignment is performed at 435MHz. I found that the deviation on 70cm is higher than it is on 2m. This appears to be a consequence of the way the radio is designed, as there are not independent deviation adjustments for the two bands. But this does explain to an extent why the deviation on 145MHz is lower than it should be.

Where I live, 70cm is completely dead and 2m is quiet so we can operate using 25kHz channel standards with no problems. Therefore I have not found this adjustment to cause any adverse effects and it certainly has improved the reach of my APRS packet beacons. Your mileage may vary.

Knott entirely as planned

Yesterday was one of those clear, blue, sunny, still, cold days that make you think it would be a criminal waste to stay inside. I decided to try another Wainwrights On The Air activation using my WOTA Pole, which had been rebuilt since Sunday's disaster. My intention this time was to visit the summit of Knott, LDW-082, followed by nearby Great Calva, LDW-095. I took the VX-8GR for APRS but this time I also took the Motorola GP-300 to use for the activation which I hoped would avoid the receiver overload problems experienced with the Yaesu.

The weather may have been bright, but I was not. Sometimes I seem to get periods of a few days when although physically I may be awake, mentally I am not. Fortunately I hadn't driven far before I realized I had not put walking boots in the car, so a complete disaster was averted. That wasn't the only silly mistake I was to make, though.

I parked at the head of Mosedale and started walking up the Cumbria Way path. I approached the structure you can see from the starting point, which turned out to be a large garden shed! The path seemed to be taking me near to High Pike so I thought I would make that my destination and visit Knott on the way back.

As I approached the "shed" I heard people making contacts with another hilltopper, Gordon G0EWN/P on Grey Knotts. I took the VX-8GR from the rucksack and made several calls using the helical whip as he completed each contact but he always replied to someone else. After ten minutes of standing around I decided to shoulder the rucksack again and continue climbing while holding the radio. I called several times when Gordon listened for "any more calls" but he was not hearing me. I don't know why that was - another case of a radio front end being overloaded by high signal levels on the fell-top perhaps?

I reached a grassy summit topped by a tiny cairn and checked my position and realized that I was further from High Pike than I thought. I also then realized that I didn't have my walking stick! I must have left it by the "shed" when I stopped to try to work Gordon! I turned round and went back. I retrieved my stick, but having wasted half an hour I decided to abandon High Pike and carry on to Knott instead.

I arrived at Knott still in sunshine with clear blue sky, the distant summits slowly disappearing in the haze. Although it was calm enough to try using the WOTA Pole supported in my rucksack I decided to use the guying kit from the MFD that I'd brought with me in case of windy conditions to avoid the trouble I'd had on Sunday. That cost the antenna some height, but on the plus side it allowed me to operate sitting down which I was glad of as I'd been climbing for over 2 hours by this point. Whilst I ate my lunch I connected the VX-8GR to the WOTA Pole and it was picking up APRS packet bursts from as far afield as Norway and Holland. VHF conditions were obviously up.

When I finished my lunch I connected the GP-300 to the antenna. This was when I discovered I'd brought the wrong speaker-mic. One of the hazards of owning too many hand-held rados I suppose! It was not a major problem of course, as I could use the radio without it. I made several contacts from the summit of Knott the most distant of which was G6ODU in Ormskirk, Lancashire, not a bad haul from the North Lakes.

The wind was so calm my Olympus voice recorder logging device was able to make a high fidelity recording of the activation. In case anyone is interested to hear what it sounds like at the sharp end of a WOTA activation here is a recording of about 8 minutes of activity. The loud, punchy audio from the Motorola GP-300 really helps so you can hear both sides of the contact equally well. Some of the quality has been lost compressing it down to an MP3 file of reasonable length but it's still almost like being there!

I would have liked to stay on the hill longer to see what else I could work, or even move on to Great Calva to activate that, but a thick bank of mist was approaching and I didn't want to be up there in mist. There are few clear paths on these infrequently walked grassy summits and without any landmarks to aim for it would be easy to get lost. Even though the visibility was clear I still went the wrong way off the fell and hit the Mosedale to Skiddaw House path much closer to Skiddaw House than to Mosedale. That cost me an extra 3km or so of walking to reach the car, by which time the mist had arrived and the sky was a grey murk.

This was long walk for only one summit activated. I could have made more if I'd had my wits about me and things had gone according to plan. But on a day like this it's good to be out however many summits you activate!

Braap analysis

One problem I have noticed with the PIC TNC I recently built is that it is less tolerant of different packet signals than any of my radios. It decodes my two Kenwood transceivers just fine but it will only decode the VX-8G at a specific audio level that is impossible to set when using the fixed output of many radios. And it won't decode my WX-1 weather station at all.

My Kenwood TH-D72 won't decode the weather station either. However it is the VX-8GR I am more concerned about. With the volume of the packet channel turned up, it's braaps sound a bit thin and weedy compared to those of the Kenwoods and other radios I hear over the air. I thought that I would try to analyze the signals to see if this would give me an idea of what was causing the problem.

I used Spectran, the only free software I know that will do audio spectrum analysis. The receiver was the old Kenwood TH-205E, which being over 25 years old had IF filtering wide enough not to cause any deviation limiting. Each capture was made at the same volume level so the signal levels shown should represent the relative signal deviation.

Because packet bursts are fleeting it took a few attempts to capture the screen at just the right moment. But eventually I obtained plots for each of four radios, including the weather station. Incidentally I am puzzled that the spectrograms show a comb of frequencies. I thought 1200 baud packet was FSK using two frequencies, 1200Hz and 2200Hz. I have seen this before when using sound card decoder software for packet but I have always been puzzled by it.

The top two plots are for the two Kenwood radios. They look pretty near identical. In the absence of any test equipment to actually measure the deviation levels I have to assume that these two radios were correctly set up at the factory and represent the ideal signal to aim for. It is interesting that the highest frequency which I would have assumed to be 2200Hz actually peaks at about 2235Hz. The peak closest to the lower frequency of 1200Hz is actually 1185Hz. But there are six peaks at intervals of about 150Hz between the two and some spaced the same distance going below the lower frequency. I'm sure there's a reason for it.

If you look at the plot for the VX-8G the top peak is at about 2230Hz and 5dB weaker than the corresponding peak of the Kenwood traces. The other peaks are lower still with the one at about 1180Hz around 8dB lower than that from the Kenwood. Some VX-8 users have complained about low packet deviation of the radio but have been told by Yaesu that it is within specification. As far as I know there is no adjustment to increase it. You would have thought from this that I would need to increase the audio level to get reliable decoding of the VX-8 compared to the Kenwoods. In fact, I have usually had to reduce it a little. As previously stated, the volume setting at which the PIC TNC will decode the VX-8G is quite critical, whereas the Kenwood signals would decode over quite a wide range of audio input levels.

When you look at the signal from my WX-1 weather station, which is modulating a Radiometrix VHF transmitter module, the peak signal levels are close to that of the Kenwoods. The lower frequency components are in fact a couple of dB stronger. However, it's clear that the frequencies are too high. The top peak, which should be 2200Hz, is about 2290Hz. And the one closest to 1200Hz is about 1230Hz. When setting up my FoxTrak APRS tracker I had to set the frequencies using the PIC calibration routine as low as they would go before my TH-D710 would decide it, so clearly it is the frequency offset that is responsible for the packets not being decoded. The WX-1 firmware unfortunately does not have a calibration procedure. Either the PIC clock crystal needs to be slowed down a bit or I need to make a change in the source code to shift the frequencies and recompile the firmware.

But it's the VX-8G that most bothers me most. I wish there was a way to boost the level of its packet modulation and make it more like the Kenwoods.

Foul!

Following a tip from the VX-8R Yahoo group I ordered a high capacity 2000mAh FNB-102Li battery for my VX-8GR from a dealer in Spain that was selling them for EUR 28.50. The website couldn't calculate shipping to the UK so I received an email asking me to order two connectors the cost of which equalled the cost of the shipping, making a total of EUR 36.80 - still much less than the price of the Yaesu product even when ordered from Hong Kong. After this was sorted out the battery was with me five days later.

My pleasure at the speed of the shipping soon turned to dismay. Yaesu chose to make the VX-8 belt clip attach to the battery pack. I don't know whether the accessory batteries bought from Yaesu come with a belt clip to attach to them but this one doesn't, so if I want to interchange this battery with the one that came with the radio one of them will have to be used without a belt clip.

But worse was to come. The battery will not charge in the drop-in charger while it is attached to the radio! The charger has a platform which, as owners will know, is deeper than the radio with the stock battery - presumably to accommodate the thicker higher capacity version. But with this battery attached, the front of the radio fouls the lip at the front of the charger where the status LEDS are, preventing it from dropping the last tenth of an inch necessary for the battery contacts to make contact with those on the charger.

Is this a general problem with the FNB-102Li and the VX-8GR (in other words, is the GR thicker than the DR and my charger doesn't allow for this?) or is it just this third-party battery that is thicker than the one from Yaesu and causing the problem? I'm having to take the battery off the radio to charge it, but that rather spoils the convenience of having the drop-in charger.

A matter of timing

I'm finding it hard to love the new Kenwood TH-D72. Despite the fact that it has a more sensitive GPS, a proper TNC that you can interface to computer APRS or packet software and is firmware upgradeable, I'm steadily coming round to the opinion that the VX-8GR is the better performing, more usable radio.

Things I don't like about the TH-D72 is that it is bigger and heavier, has a screen that gives far less information at a glance than the corresponding screens on the Yaesu and has poorer ergonomics. I have also been harbouring a suspicion that its packet modem was less sensitive. Today I think I discovered the reason.

I recently built a Fox Delta weather station that outputs AFSK packet directly into a radio. I noticed that although my Kenwood TM-D710 and my VX-8GR decode it's S9+ packet bursts the TH-D72 didn't. I thought it might just be a case of adjusting the deviation but I tried the weather station on two different radios adjusting the audio level from nothing to definitely clipping and could not find a setting at which the D72 would decode anything.

Recently I set up a low power APRS repeater in the shack. It is a sound card TNC (TrueTTY) driving a low power UHF radio (the FT-817ND) running into a dummy load, which is connected to the aprsg gateway software. This gates everything that is going on in APRS within a specified radius to UHF so that I can monitor activity and reply to messages using an APRS HT anywhere I am in the house. This has been working fine with the VX-8GR but last night I forgot to switch it off and the battery was dead so I tried monitoring using the TH-D72 instead. Nothing was copied!

Again I tried an entire range of audio levels into the radio but while the VX-8GR and the TH-D710 both decoded the packets over a wide range of settings the D72 didn't decode anything. I was using TrueTTY into my USBlink home-made VOX-based digital interface. I wanted to try different software (AGWPE) and a different sound card but Windows got confused having different USB sound devices connected to it and it is also a dog at handling serial ports. I have real serial ports occupying COM2 to COM5, a pair of virtual ports mapped between COM8 and COM9, and other USB serial devices I have used in the past have been assigned to COM1,6 and 7. AGWPE can only use COM1 to COM9 and trying to change the USB serial device to use one of the three currently unused ports in this range resulted either in Windows complaining that the port was in use even though it didn't show in Device Manager or the application saying that the port did not exist even though it did show in Device Manager. Eventually things seemed so screwed that I restored back to this morning and gave up.

Having restored the system and checked that everything worked again one more idea occurred to me. TrueTTY allows you to specify the exact sample rate used by the sound card, to compensate for timing errors. Instead of 11025Hz I tried 11000Hz and while the D710 and the VX-8 still decoded the packets the D72 still didn't. I then tried 11050Hz and lo and behold, the D72 started decoding!

It's impossible to make a suggestion that there is something wrong with a radio in the owners' groups on Yahoo as so many people can't bear to consider the fact that something they bought is anything less than perfect and will come up with any alternative explanation they can think of. So I'm sure that the problem I have described will be blamed on the AFSK modulation being slightly off-frequency which, of course, it is.

However in the real world a radio will be used to receive transmissions from people whose modulation is off and don't know it or may not even have any way of adjusting it. A modem that is more tolerant of these deviations from the precisely correct will decode more signals than one that expects the modulation to be spot on and in that respect the VX-8GR is by far the most easy-going and most sensitive of all the APRS radios.

It's just frustrating to hear braaaps and not see them decoded, so I think the Yaesu is going to be the one of these two APRS hand-helds that I hang on to.

Successful outcome

I finally solved the problem with the cable I was trying to make to interface my VX-8GR with the computer, as described in my last post. As I had begun to suspect, the trouble was caused by the 2.5mm jack plug not fitting properly in the VX-8GR data port socket.

As suggested by one of my readers, I tried the cable in the COM port of the TH-D72. Although I couldn't figure out how to make data appear on this port, I did see some output when turning the TNC on and off which suggested my cable did work.

I then tried it back on the VX-8GR and used my oscilloscope to look for anything digital. I didn't see anything. I then tried another 2.5mm jack with the sleeve off so I could get the 'scope probe on the solder tags and with a firm press it went in with a click. I now saw -5.6 V on the TX pin - clearly an RS-232 signal level.

The jack I originally used had a plastic sleeve or cover and the diameter of the base was just a bit too much to allow it to go all the way in. One with a metal sleeve had a slightly smaller diameter base. The metal sleeve itself interfered with inserting the jack, but I could put the plastic sleeve on that jack and it would still go in. So that, finally, is what I did, and I now have a VX-8GR PC cable that works. It also works with the COM port of the TH-D72 should I find a use for that.

As a ham and electronics enthusiast I don't believe in buying things I can make myself, but sometimes making it yourself can turn out to be more trouble than it is worth!

Incommunicado

I have spent a frustrating couple of hours trying to make a PC cable to communicate with the VX-8GR. In the VX-8 Yahoo group it was stated that the cable is the same as for the Kenwood TH-D7AG a diagram of which is given in YO3HJV's blog. It was also pointed out to me that there is a diagram in the back of the manual - the one place I never thought to look!

It is easy enough to make up. No level shifting components needed. Just a 2.5mm stereo jack for the radio end and a 9-pin D plug for the PC end. But the damn thing refuses to work.

I have tried a Prolific USB to serial adapter and an FTDI one. I've tried the FTBVX8G software and I've tried a terminal program to see if I can detect any data. Nothing. Nada. Incommunicado. I know the cable is OK because if I short between tip and ring of the jack plug I can type in the terminal program and see the text I typed echoed back over the connection.

The only thing I can think of is that the standard 2.5mm stereo plugs I have here are a bit too short. It seems to me that the  plug isn't locking firmly into place, more that the radio is trying to push it back out again. It's as if the tip needs to be a bit longer to get past the spring loaded contact in the socket. I measure 7/16in from the base of the plug to the tip of it. I had a similar problem trying to make a cable to send audio from my FoxTrak APRS tracker into my Motorola GP300. Then I had a plug from a speaker mic to compare it with and I could see that it needed to be longer.

Perhaps someone who has a VX-8G PC cable that works could measure the plug on theirs. Or perhaps someone will spot the stupid wiring mistake I've made from the photo I've posted.

APRS Handies head to head

My long awaited package from Martin Lynch was finally delivered by UPS on Saturday afternoon and as one reader correctly guessed, it was a new Kenwood TH-D72! I was lucky. The UPS tracking page had been changed to say delivery was rescheduled for Monday, so we went out on Saturday morning. You can imagine how happy I would have been to get home and find a card through the door to say UPS had tried to deliver it! I was pleased to receive the radio and although I did consider wrapping it and putting it under the tree until Christmas Day, the chance of being the first blogger to write about it was too great to resist.

This is not meant to be a review of the Kenwood, more an account of my first impressions of the radio and how it compares with the Yaesu VX-8GR which I have been using for the past few months. The first thing you notice is that the Kenwood is quite a bit bigger than the Yaesu. It's taller, thicker and heavier. Although I think the Kenwood is nicer looking, the Yaesu feels a bit more rugged and I think its plain black finish would take knocks and scuffs better than the Kenwood's metallic grey finish. I'll probably need to get a protective case for it.

The additional thickness and weight can partly be attributed to the Kenwood's battery pack which has 1800mAh capacity, compared to the Yaesu's 1100mAh. This should translate into longer endurance in the field. Yaesu does offer an 1800mAh battery pack for the VX-8 series but it is an optional extra for quite a lot more money. Still, there is no question the slimmer, smaller VX-8GR slips more easily into a pocket for about-town use.

The TH-D72 is a dual band 2m/70cm radio so it it is more directly comparable with the Yaesu VX-8GR than with the tri-band (quad band in the USA) VX-8DR. Both radios have an integral GPS rather than the expensive optional GPS of the VX-8DR which must be fitted to an even more absurdly expensive clunky looking bracket or to a specially made Yaesu speaker mic. (Having said that, the Yaesu GPS options are good value compared to the add-ons for Icom's D-Star radios - talk about rip-offs.)

The TH-D72 comes with the usual pathetic SMA socket for the antenna and an equally pathetic dual band dummy load, er, I mean whip antenna. The first thing I did, and I mean literally the first thing, was to fit one of my SMA to BNC adapters so I can use any of my collection of BNC whip antennas with the rig. The SMA socket sits deep in a large recess on the top face of the Kenwood, so I was able to use one of the chunky gold plated adapters rather than the slimmer black one that I use on the VX-8GR.

I checked with a piece of paper to see if the adapter tightened all the way down to the body of the radio, which is essential to avoid the risk of snapping the SMA at the first accidental knock. It didn't, so I added a steel washer to fill the gap. I covered the knurled base of the adapter with a layer of self amalgamating tape to hide the gold finish and once an antenna is fitted you wouldn't know that the BNC socket was not standard equipment. Why couldn't the manufacturers fit one in the first place? By the way, neither of these radios come with a wrist strap - the ones shown in the picture were salvaged from old mobile phones in the junk box.

One of the main reasons I decided to get the Kenwood TH-D72 even though I had the VX-8GR was that I was very unhappy with the performance of the Yaesu's GPS which is slow to acquire a fix and usually can't manage it at all from inside the house. I found this a real nuisance as often I just could not be bothered to hang around waiting for it, while the chance of acquiring a fix once you are on the move is even worse. As you can see from the picture above, the Kenwood has got my position while sitting on the bench being photographed while the Yaesu's GPS screen was (and remained) blank.

The Kenwood has a display to show how many GPS satellites it is receiving and as you can see from the picture above, even on the bench it does quite well. This is a nice screen to have, but with this exception I prefer the Yaesu VX-8 display which shows more information at a glance. The Kenwood display often consists of a couple of short lines of text and you have to page through several screens to get all the information. However I do like that the Kenwood position screen shows the grid locator square - the Yaesu doesn't.

The TH-D72 has the ability to plot your track and store it in memory - not something I can see myself using though. What I do consider very useful is the ability to enter and store the co-ordinates of several locations or waypoints. You can then select one and one of the Position pages will display your distance and bearing from it. This will be very useful during WOTA operating as I will be able to enter the exact co-ordinates of the summits I intend to visit, eliminating the difficulty sometimes experienced of identifying the summit on the ground!

The TH-D72 is virtually a hand held TM-D710. It has almost the same functionality of its bigger mobile brother, in fact more: it supports the Kenwood Sky Command remote control system which my European D710 doesn't. A pity - it would have been fun to see if I could have used it to remote control my Elecraft K3, which uses a command set similar to the TS2000.

In common with the D710 the D72 has hierarchical menus. Personally I prefer the menu system of the VX-8 series, which has just two linear menus, one for radio settings and one for APRS. I know where the ones I most often use are and can quickly zip to them using the rotary control. The Kenwood menus require a lot of clicking with the four way directional button thingy.

If you want to connect your VX-8 to a PC for memory management you need to purchase third party memory management software and an interface cable. Kenwood provides the memory management software free and the TH-D72 has a USB port which can be connected to your computer using a provided, but in any case standard, USB cable - a significant saving. Through this cable you can not only manage the memories you can also edit all the radio's settings and access the built-in packet TNC. This appears to be completely compatible with the one in the TM-D710. I just changed the COM port number and APRSIS32 as set up for the D710 was immediately able to use the D72 instead. A menu option allows the internal GPS data to be output over the same serial connection. I haven't experimented with this, so I don't know if this can be done at the same time as accessing the TNC or whether APRSIS32 would be able to take advantage of it.

Hopefully the TH-D72 will, like the D710 (and unlike the Yaesu radios) be software upgradeable. I discovered, to my disappointment, that my APRS repeater objects being transmitted by my G4ILO gateway were displayed by the VX-8GR but not by the Kenwood. The packets were received but were apparently considered to be invalid. A bit of research by Kai Gunter, LA3QMA led to the conclusion that this is a bug, not just in the TH-D72 firmware but in the TM-D710 as well, as the same objects were displayed by older model Kenwoods. The problem is apparently caused by the time-stamp in the objects created by APRSIS32 which is in local time (ending in 'h') instead of zulu time (ending in 'z'.) The objects are correct according to the APRS spec, so the Kenwood should display them.

The TH-D72 is full duplex. That is, it can receive on 70cm while transmitting on 2m or vice versa. There are very few current model radios that can do this, one of which (the Alinco DJ-G7) doesn't do it very well as 70cm is severely desensed by the 2m transmission. This would make it a good choice for FM satellite operation allowing you to hear your own signal. One of these days I will try this, I just need to get round to making a suitable dual band antenna.

Another neat feature of the TH-D72  is the nine EchoLink memories. This allows the radio to store the DTMF sequence needed to connect to up to nine different conferences or nodes so you can recall them by name and transmit them to your local EchoLink repeater. If you use EchoLink it is a real boon as I can never remember node numbers - heck, I still can't remember my mobile phone number!

The Kenwood TH-D72 is quite an amazing radio packing an incredible number of features into its small form factor. However I would not go so far as to say it is a better radio than the VX-8GR. There are things I like and things I dislike about each of them.

• Yaesu VX-8GR - Like: smaller size, lighter weight, feels more durable, more informative displays. Dislike: deaf GPS.
• Kenwood TH-D72 - Like: sensitive GPS, editable waypoints, accessible TNC, EchoLink support, full duplex. Dislike: hierarchical menus, plain displays requiring scrolling through pages to view all information, more bulky.

In the UK, the VX-8GR is being sold for quite a bit less than the TH-D72, even at the discounted price I got from Martin Lynch. If you don't want to connect the radio to APRS software on a PC, aren't bothered about getting your GPS position indoors and never use EchoLink then you probably won't think the Kenwood is worth the extra money. Though it does include a higher capacity battery as standard and if you want memory management software then both this and the connecting cable will cost you extra for the Yaesu.

I'm still making my mind up which of the two of them is going to be the keeper but I suspect it's going to be the Kenwood.

On the cliffs in West Cumbria

Cumbria is famous as the county of the English Lake District but it has more to offer than mountain walks. I don't agree with Alfred Wainwright who said he could not see the point of walking round a mountain when you could climb to the top of it. There are many beautiful walks in the valleys and round the lakes which my wife (and my knees) much prefer over climbing and descending even if they don't offer much scope for making radio contacts. Less well known, but just as spectacular, are parts of the coastline. One of our favourite outings is to park in the village of Sandwith and go for a walk along the cliffs. This is where we went last Sunday.

Map of the walk (from aprs.fi Google Maps)

The map of the walk shows the path that was tracked on Google Maps APRS, with some additions by me where my position was not tracked.

I was using my VX-8GR with the 5/8 telescopic whip in my rucksack, as shown in the picture on the right. I operate pedestrian portable like this when I don't expect to encounter too many people who will give me strange looks or think I am a dork. The radio sits in a little mesh pocket on the side of the rucksack which was probably meant to carry a water bottle. The antenna is supported by pushing it through a string loop attached to one of the zips of the main pocket of the rucksack. It is quite stable and does not flex the spring or the mounting at all.

I don't know what the SWR is like. Possibly it isn't that good as the radio does not have me holding it to provide a ground plane. Perhaps I should try clipping a 19 inch "tail" to the outer ring of the BNC connector as a counterpoise? But even without it, it worked well. Most of my position beacons were received by MM1BHO across the water in Scotland so I was able to see the track after the walk. I also received some interesting APRS DX, of which more later.

But back to the walk. The weather was glorious, as you can see from the pictures. The temperature was around 20 degrees Celsius with only a slight breeze. The view from the cliffs was spectacular and always reminds me a bit of Cornwall. To think that people pay money to come on holiday to places like this!

We walked for about an hour along the cliffs, stopping now and again to watch some birds through binoculars or just take in the view. This is an important area for wildlife and the Royal Society for the Protection of Birds (RSPB) has set up several places where you can watch them with safety on the edge of the cliffs.

You can walk right along these cliffs as far as St. Bees, where there are people and cafes and ice cream kiosks. But we usually stop at Fleswick Bay, a beach backed by the high cliffs that is always quiet and secluded even in the height of the season because it isn't possible to reach it by car, it can only be accessed by footpaths. We call it our private beach because we often have it to ourselves.

This Sunday we didn't go down to the beach because we saw from the clifftops that the tide was in and the sea was right up to the foot of the cliffs. So we had our picnic lunch in one of the RSPB birdwatching areas instead. I made a couple of FM contacts using the VX-8GR, including one with another portable station on a 2,500ft mountain top in Wales. Then we started the walk back.

On the way back I heard the VX-8GR braaping away constantly such as I hadn't heard since we were in Prague. On my return home I scrolled through the station list and observed that for a couple of minutes between 12:28 and 12:30 UTC I had received beacons from several DX stations including F4EQD-1 and OZ2DXE-2. These beacons had actually been digipeated by a station in south west England but that was still an amazing distance to receive signals on a VHF handheld, even if I didn't hear them direct.

The glorious weather had also produced fantastic tropospheric propagation which was enjoyed by people in most parts of Europe. I wished I had climbed to the top of a mountain as I would certainly have heard more there than I did down on the west coast and perhaps have worked some real handheld VHF DX. But you can't predict propagation and it was still a wonderful day's walk.

Nice Nagoya

As regular readers may recall, I have a pathological hatred of SMA connectors when used as antenna connectors for hand-held radios, which has become even more entrenched since I had the centre pin of the TH-F7E stock antenna break off in the adapter I use for testing such antennas on my antenna analyzer. I now have an SMA to BNC adapter permanently installed on my VX-8GR. The picture on the right shows my latest adapter which is anodized black and looks like an integral part of the radio. The previous one I used was gold plated with a knurled body and whilst it worked perfectly and provided a robust fitting for the BNC antennas it looked a bit ugly.

If you never change the antenna on your HT then one of these adapters isn't necessary, but SMA connectors were never designed for multiple connections and disconnections (in one email group I saw someone state they were rated for 100 disconnections) so if you want to change between a short stubby antenna for inconspicuous local use and one with more gain the BNC adapter is the way to go.

All of my BNC whips are 2m antennas, which is fine most of the time as almost all my operating is done on 2m, but there are rare occasions when I might want to use 70cm and removing the BNC adapter in order to attach the stock antenna kind of defeats the object of it. So I ordered from eBay a Nagoya NA-701 antenna which is a short dual band whip similar in size to the ones supplied with amateur dual band handhelds but with a BNC connector.

I tried it out on my antenna analyzer and it showed a nice sharp SWR curve with the minimum around 147MHz. It could be better, but it's closer than some stock antennas I've tested. I couldn't check it on 70cm as my antenna analyzer doesn't go up that high.

I need to devise way to make comparative tests of all these HT antennas, because asking for signal reports or seeing if you can hit a repeater is a pretty crude measure of performance that won't reveal small differences. This little antenna doesn't perform as well as a six inch monoband helical on 2m, nor a quarter wave telescopic, but that is only to be expected. The beauty of the BNC adapter is that if you need a gain antenna you can easily whack on something like my 5/8 wave Black Whip, which you certainly couldn't use with a standard SMA connector.

Highest activation?

Steve WG0AT, Rich, AC7MA and Guy, N7UN recently returned from their expedition to activate Huron Peak in the Sawatch Range in Colorado, USA, for Summits On The Air (SOTA). Together with their "sherpa" goats Rooster and Peanut, they took a GPS-equipped Yaesu VX-8R so people could track their progress.

You can see a slide show of the expedition here.

I rather like the idea of using goats to carry the heavy equipment but I think you'd get some funny looks in the hills around here. This has made me wonder what has been the highest SOTA activation to date. Has anyone activated Mount Everest yet? I bet that would create a pile-up!

VX-8GR in Prague

As regular readers will have realized from my previous post, I have been on holiday in Prague, capital of the Czech Republic. I won't bore you with details of where I went or what I did, though I have made a few comments about the holiday over on my other blog. So I will just describe my ham radio experiences over there.

Prague is quite a hilly city. The picture above was taken from the Botanical Gardens to the north of the city, looking towards the famous Zizkov TV Tower. This building, looking from a distance like an Atlas rocket waiting to take an Apollo mission to the Moon, is widely regarded as the ugliest building in Prague. But from a radio point of view it would be a good QTH. I quite like it. Apparently you can go up it to see the view, but that is something we have yet to do.

I took with me on my travels my Yaesu VX-8GR dual band APRS hand-held. Due to the language difficulty (I don't speak Czech) I didn't anticipate having many contacts with locals but I could see from aprs.fi that there was quite a lot of APRS activity in the city and I was interested to experience it first hand. I was not disappointed.

From the moment the VX-8GR was first switched on the APRS channel on 144.800MHz began receiving packets. The station list, able to hold the 50 most recently received APRS packets, filled up in about ten minutes. I was receiving position reports from fixed stations and mobiles, not only in the Czech Republic but also sometimes from Germany, Poland and Austria. I also received local weather reports, including the position of lightning strikes over a more than 300km radius and weather bulletins sent out by OK1COM. Coming from West Cumbria where you can often go a whole day without receiving anything on VHF it was quite a revelation.

I sent a greeting using APRS to Colin, 2E0XSD. By checking aprs.fi I discovered that he received it, but I didn't receive any of the acks his client sent back, nor his reply. It appears that no-one sets up their gateways to gate messages and acks for locally heard stations from the internet to RF, so the much-vaunted APRS messaging capability is essentially useless except between stations in direct radio contact.

Later in my stay I did have a messaging QSO with OK1RQ on foot in Prague with a Kenwood hand-held. Unfortunately he was busy so I never got to meet him or any other local hams. I also received greetings via APRS from a couple of other local stations.

We needed to make some local phone calls so I purchased a pre-paid SIM card from O2 for my smartphone. This included 3G data so I was able to try the APRSISCE client from Prague. I had several messaging conversations over the internet with Lynn, KJ4ERJ, the program's author. We also had our first voice QSO via OK0BNA, the Prague repeater, which Lynn was able to access through Echolink as it is connected to OK1OGA-L. I monitored OK0BNA on many evenings and heard only two other contacts take place on it. I did not hear any other FM contacts on either 2m or 70cm the whole time I was in Prague.

APRS works well in Prague because there is a network of several digipeaters and gateways within a radius of a few kilometres of the centre. The apartment where we were staying was just a few hundred metres from the QTH of OK1ALX who runs a digipeater and Igate, so most of the APRS signals I heard on my VX-8GR inside the apartment with the stock rubber duck were S9+.

The map on the right shows the tracks of some of our outings in the seven days before our return, tracked using the VX-8GR. Although aprs.fi reportedly stores position reports for a year, it doesn't appear to be possible to display tracks for specific periods retrospectively, and as I didn't have a computer with me (this was supposed to be a holiday) I couldn't capture my tracks at the time. But you can see at the top one day's walk in the Botanical Gardens, at the bottom a walk around Vysehrad, and in the middle a circular walk we made into the city centre and back along the river one evening.

Tracking an outing from start to finish wasn't very convenient, or even possible, because the GPS wouldn't pick up a fix inside the apartment and I couldn't be bothered to stand around for 3 or 4 minutes on the street outside waiting for it to get a fix before we started. Hence the big jumps from where we were staying to where we started walking.

We were on foot or using public transport and you would lose a fix whenever you got on the metro or a tram or went inside a building, and then have to wait to regain a fix when you came out. It was too much hassle. But when we were planning to just walk, it was interesting to see where my beacons were picked up, both from higher ground and from street level within the city.

I didn't use the Windows Mobile client for tracking much at all (apart for one short evening stroll along by the river) because using the GPS reduced the phone's battery life to an unacceptable couple of hours. However I was impressed by the battery endurance of the VX-8GR. After reducing the beacon frequency to no more than one every two minutes and using the 2.5W power setting, it lasted all day with enough power left for a couple of hours receiving in the evening. This is particularly noteworthy considering that the power saver was disabled (as it needs to be for APRS usage) and the receiver was constantly receiving and displaying APRS data. If only the GPS was quicker at finding its position after switch-on it would be just about perfect.

Like most hams, I guess, I always keep an eye open for antennas wherever I'm travelling. Antenna-spotting in Prague is quite difficult as every building has comprehensive lightning protection consisting of tall lightning conductors looking like VHF collinears, usually connected together along the ridge of the roof. I have never seen this anywhere else.

Close to where we were staying, in a street called Vysehradska, I noticed a shop window displaying a few old radios, some vacuum tubes, what looked like a tube tester and some other electronic bits and pieces. On the roof of the building next door I spotted an MFJ multiband HF vertical antenna. I was sure that the owner of the shop must be a ham, so we decided to go in and introduce ourselves.

Inside, the place looked more like somebody's untidy workshop than a shop. There were three elderly gentlemen, one of whom was presumably the owner. Another was leafing through a dog-eared book while the third was inspecting a vintage broadcast radio he had taken down from a shelf. They looked at us expectantly. I said "ham radio?", anticipating that someone would understand at least that English phrase, but was met with blank stares and something we couldn't understand in Czech.

Older people in the Czech Republic speak Russian, a legacy of the Russian occupation, so Olga then explained in Russian that I was a ham radio enthusiast and was interested in what they had in the shop. No-one introduced themselves as a licensed amateur, however. Instead, they told us that it was not a ham radio shop, but that there was one a few blocks away. Unfortunately Czech street names are confusing to non-native speakers, even to Olga. We didn't find it. Perhaps we will on our next visit.

GPS Interference

A week ago I received a Yaesu VX-8GR VHF/UHF APRS hand held transceiver with GPS. The transceiver performs as expected except in one extremely annoying respect - its GPS takes a very long time to get an initial fix on its position after switching on the radio. It cannot get a fix from inside the shack at all. By contrast, my HTC smartphone will get a fix in a couple of minutes whilst sitting in its charger cradle on the shack desk. Or at least, it did.

This morning I noticed on aprs.fi that the last reported position of my smartphone, G4ILO-10, was somewhere in Somerset. I started the APRSISCE application with the intent of "bringing it back home" by sending a position report with the correct location. But after ten minutes the phone had not managed to get a fix.

I switched off all my radio equipment in case one of them was an interference source, and rebooted the phone, and eventually after several more minutes it obtained an accurate fix. I am beginning to suspect that something is interfering with GPS reception in the area of my house.

If you Google "GPS interference" you will find links to numerous articles and research papers raising concerns about what is apparently an increasingly common problem. One article states that a directional television receiving antenna widely available in the consumer market contains an amplifier which can emit spurious radiation in the GPS L1 frequency band with sufficient power to interfere with GPS reception at distances of 200 meters or more. Other potential interference sources include spurious outputs from TV transmitters.

Another website states that "We are seeing increasing evidence of GPS interference and also apparent erratic behaviour (e.g. mis-reported location)" and provides a form for reporting cases of interference. This page provides links to two reports on the issue which unfortunately require registration in order to access them.

Have other amateur GPS users experienced difficulty in receiving the satellites or an increase in inaccurate position reports? For many GPS applications the effects of this could have rather greater impact than a radio ham's inability to report his position to aprs.fi. Perhaps the US administration was rather hasty in its decision to decommission Loran.

Yaesu VX-8G

A recent addition to the G4ILO shack is a new Yaesu VX-8G hand held transceiver. In case you are thinking that I need professional help over my addiction to hand held radios you may be right - however a week or so ago I received an email from someone who has a collection of 150!

Long-time followers of my blog may recall that less than a year ago I bought a Yaesu VX-8E APRS transceiver with GPS. However I found that the usefulness of APRS was limited by the lack of digipeaters and internet gateways in this part of the world. I decided to use a smartphone based APRS client, APRSISCE instead and sold the VX-8E shortly afterwards.

Using the cellular network instead of amateur radio has its advantages but it eliminates the interest of seeing how far a little 2m RF can go. Interest in APRS has increased in this area over the last few months so I decided to give RF another go. In the meantime, Yaesu brought out an improved version of the original VX-8R called the VX-8DR and a lower cost version called the VX-8G. So I didn't regret my decision to sell the VX-8R as it allowed me to acquire the updated version.

One of the things I really disliked about the VX-8R was the clunky way the GPS attached externally to the radio (and the absurdly expensive fixing bracket.) The VX-8R (and the updated DR) has a number of other features that I never used and didn't need in an HT: 50MHz coverage (including AM), short wave receive (which was useless anyway without an external wire antenna), a barometer/altimeter and a temperature sensor. Nor did I care that it was submersible. I did lose a brand new HT in the Solway several years ago, but as I didn't immediately notice it had fallen off my belt I never found it again.

The VX-8G lacks these unwanted features and can be set to vibrate when you receive an APRS text message - a new way to get a thrill out of amateur radio! More importantly it has the GPS built into the radio which makes for a much neater package. It costs about the same as a VX-8DR without the GPS option.

The VX-8G is not available yet in the UK so I purchased it from Solid Radio, an eBay trader based in Hong Kong. This was the most expensive thing I have ever bought from a Far Eastern trader and I felt like I was taking a bit of a gamble, but the radio arrived in just over a week and with no unpleasant surprise on delivery.

The VX-8G looks very similar to its older brother but is a little slimmer and lighter. I seem to remember that the body of the VX-8R was metal, or else it had a substantial chassis that added to the weight. With the standard battery installed the VX-8G is noticeably lighter than my Kenwood TH-F7E.

The Yaesu's GPS takes much longer than the one in my hTC smartphone to acquire a signal. In fact after waiting several minutes on first turning on the radio I started to worry that the GPS wasn't working so I stood it out in the garden on a table where it eventually established its position. On subsequent occasions it has still taken a few minutes to fix its position which is a bit annoying.

Operationally the radio appears to be the same as the VX-8R and the menus are very similar. One of the new features is SmartBeaconing which varies the frequency of position reports according to your speed and whether you have changed direction. There are different settings for this depending on whether you are walking, cycling or driving. The original model would only send position reports on a fixed time interval. Once I had enabled SmartBeaconing it sent a very accurate track of my walk.

It is too early to say with any precision what battery life is like but initial impressions are that with the GPS enabled it is pretty poor - a criticism that unfortunately is also true of the smartphone. I used to have a navigational GPS called an iFinder GO2 which ran for about 18 hours on two AA batteries so low current consumption GPS devices do exist - why doesn't Yaesu use them? In the VX-8 radios when you use APRS the problem of short battery life is compounded by the need to disable the power saver (which causes the receiver to listen in short bursts rather than all the time) so you don't miss the start of a beacon or message sent by another station. The VX-8G uses the same batteries as the VX-8R and DR models so a higher capacity pack available, but it is quite expensive.

I am pleased with the VX-8G so far and am looking forward to discovering where I can be tracked from. I think APRS holds some of the same fascination as WSPR on the HF bands in that it is interesting and sometimes surprising to see how far your low powered signals can travel.

I don't know when the VX-8G will be introduced in the UK or what its UK retail price will be but I expect it will still be quite an expensive radio. A pity, as I think the cost puts a lot of people off discovering APRS for themselves.

New VX-8DR

Rinse, PD2RPS, dropped me a note to alert me to the fact that Yaesu has introduced an updated version of the VX-8R (US version of the VX-8E) called the VX-8DR. The new version has several improvements in the APRS functionality, but they are pretty minor and I won't be losing any sleep over not having them.

• Smart Beaconing Function. When using APRS for position tracking, the beacon timing is automatically adjusted to your travelling speed and location instead of using a fixed interval. This is the most useful enhancement in my opinion.
• Heads up compass display to the GPS Screen. Your traveling direction is always toward the top of the display. This might be useful if you are using the VX-8 as a navigation device, but as it can't display maps that isn't very likely.
• The number of DIGI-PATH route settings is increased from 1 to 7. Handy I suppose, but not too hard to work around.
• The number of Station List memories has increased from 40 to 50. Yawn.
• The number of APRS Message memories has increased from 20 to 30. Yawn.
• DIGI-PATH route indication function. The APRS Packet data includes Digipeater routing info. Yawn.
• The Message received LED flashing rate is selectable. Zzzzzz.

If you are not as underwhelmed as me by these new features then you'll be interested to know that the old model can be upgraded - but disappointed to discover that this can only be done by returning the radio to Yaesu. It is not, apparently, field upgradeable using your cloning cable. I'm guessing that this may be because Yaesu licensed the Smart Beaconing code from HamHUD Nichetronix and by making it a DIY upgrade there would be no way to ensure that everyone who applied it paid for it.

I think Yaesu missed some real opportunities here. Predictive text, as used in any mobile phone, would make APRS text messaging much less tiresome. And, even without maps, the ability to display your position graphically relative to other received APRS objects - and the ability to enter objects manually - would turn the radio into a half-useful navigation device.

This upgrade is currently only available in the USA. The European VX-8E will presumably need a different upgrade.