Derventio

I have been itching to try venturing further afield and thought we might go down to the river Derwent at Papcastle. I carried the Kenwood TH-D72 on my belt to track the walk using APRS and see how far we got. When we reached the path down to the river we saw a paper sign saying "Derventio." Olga thought - wisely with hindsight - that it would not be a good idea to walk down to the river as we would then have to climb back up again. We walked a bit further along the road and looked down towards the river where we could see substantial excavations were taking place. This looks like being a major archeological site. One day when I'm just a bit fitter we will go down and take a closer look.

We continued our walk with a loop through the village of Papcastle, then returned home the way we had come. On the way I heard and worked Richard G1JTD portable on the summit of Great Calva, and Liz M6EPW on my local SOTA summit of Watch Hill. That will undoubtedly be the first summit I will attempt but at the moment it is still too far - about 3 miles from our front door.

I was pretty tired and very sweaty by the time we got back to Cockermouth but I resisted Olga's suggestion that we finish the excursion by taxi. Although what we had done was an easy walk by normal standards this was my most ambitious outing since finishing my treatment.

When we got home I could see that our track had been perfectly recorded by APRS. I was happy with that - and with the two contacts I made. I had only been using one of those stubby antennas about 5 cm long which are a couple of dB down on a rubber duck.

I saved the track as a GPX file and then produced a report using one of the online GPX report generators. According to the report we had walked exactly 4 kilometres. 1.5km of this had been climbing for a total ascent of 87m. To me it felt as if I had just climbed Scafell Pike!

Third-party Kenwood accessories

Ebay is a good place to buy accessories like speaker/mics and headsets for your radios. A few years ago I used it to buy a speaker/mic for my Kenwood TH-F7E. After I sold that radio I used the speaker/mic with my TH-D72. When I tried it with my old TH-205E however I found that PTT didn't work. I soon established that the reason was the genuine Kenwood accessories used a monophonic 2.5mm plug with only two contacts, tip and sleeve, for mic audio and PTT. The third-party accessories from eBay used a stereo 2.5mm plug with tip, ring and sleeve, but there was no connection to the ring. It looked as if the plug in the radio was trying to make contact in the area of the ring. This obviously was OK for newer Kenwood radios but with the 205E there was no ground connection for the PTT.

Ring and sleeve of the 2.5mm plug should be connected

My first thought was to open up the speaker mic, find the wire connected to the ring and connect it to ground. However I soon found that the cable of my speaker/mic had no wire connected to the ring at all. My only option was to try to bridge the two contacts together using solder. This I did, and the speaker/mic then worked with the TH-205E.

The Wouxun KG-699E and the Baofeng UV-3R+ also claim to use accessories with a Kenwood-compatible plug but just like the 205E I found that PTT did not work. I have just performed the same modification to the plugs on a "Kenwood-compatible" headset/boom mic and also one of the earpiece/mics that came with the Baofeng and Wouxun so that they would all work with all four radios. It is easy to do, but you need to take care as it's easy to melt the plastic parts of the plug and you could easily ruin it if too much heat is used.

Using a sharp craft knife cut away a small section of the black plastic insulation between the ring and the sleeve of the 2.5mm plug to reveal an inner metal sleeve. Open this up a bit more using the edge of a jeweller's file. Then make a solder bridge between the ring and sleeve. You need to apply heat using the edge of the soldering iron bit to the inner sleeve in order that the solder will bridge the gap. Apply the soldering iron for as short a time as possible to avoid melting the plastic insulation and destroying the plug. I used Blu-Tac to hold the plug in a steady position whilst soldering.

After you have bridged the contacts use a jeweller's file to remove any excess solder from the plug. You should also smooth the plastic insulation between the plug contacts which may have melted and bulged a bit. The plug should be completely smooth between the contacts, the solder bridge and the insulation. It should plug easily into the socket on the radio. If it needs a firm push then try a bit more filing until it goes in easily. You don't want the plug to get stuck in the radio nor for it to damage the socket contacts if force is needed to insert or remove it.

I accept no responsibility for damaged plugs or radios as a result of trying this modification. However I have done three of them now with success each time so it is possible with care. Now my "Kenwood-compatible" accessories will work with old and new Kenwoods as well as the Baofeng and the Wouxun.

The meaning of >F

I have been playing with using the Kenwood TH-D72 as a standalone digipeater and fired up the FoxTrak APRS tracker I built last year. The FoxTrak is a TinyTrak clone using DK7IN firmware. I had not noticed a problem before when using a TNC connected to PC software, but now I found that the D72 will not display the FoxTrak's packets. Instead, it interrupts the frequency display and puts >F G4ILO-12 on the first line of the display. The packets are digipeated but they don't appear in the radio's list of received stations.

I'm guessing that >F is some sort of error status but it is not listed on page APRS-3 of the user manual where the other status indicators are listed. Does anyone know what it means, or how to configure the FoxTrak so that the Kenwood will display the beacons?

Dodd [LDW-174] all to myself

The weather forecast suggests that the fine spell we have enjoyed for the last few days - which has caused the G4ILO shorts to be brought out of the wardrobe unusually early - is going to end soon. So I thought I would try an activation this morning of the small summit of Dodd, LDW-174 for Wainwrights On The Air. Being a tightwad, I didn't want to pay the Forestry Commission's exorbitant charges to park at the visitor centre so I parked off the road at a spot about a mile north of the official car park. I'll happily walk an extra two miles to save £6.50!

I was afraid this well-known parking spot would be full but in fact there were only two other cars there, a silver Nissan and an old BMW that was very dusty and looked suspiciously as if it might have been there a while. I set off along the path and had hardly walked a few paces when I saw some car keys in the undergrowth beside the path. "I bet they are BMW keys" I thought to myself as I picked them up and sure enough they were.

Now I had a dilemma. Perhaps someone had dropped their keys and would be coming back to look for them, so I should leave them where they were. It was just a gut instinct that made me suspect the BMW had been stolen and some thief had left it in this quiet spot and thrown away the keys before switching to another car. If it wasn't a stolen car, surely it soon would be if I left the keys so close to the vehicle itself. So I decided to walk to the visitor centre and hand the keys in, explain what had happened and suggest they called the police to investigate.

This I did, before beginning the ascent of Dodd up the forestry road. It is a rather dull plod until you reach the col between Dodd and the Ullock Pike ridge and the path curves round Dodd's conical summit until this view over Derwentwater opens up. Then it is another short upward plod until you reach the summit (top picture.)

As I reached the higher altitudes it was clear that the stiff cold wind that has been a feature of the entire weekend and made conditions a lot less pleasant than the photos suggest was still with us. The WOTA Pole was still broken (and probably won't be repaired) so in its place I was using my new rucksack mounted telescopic 5/8 vertical. This is the old telescopic 5/8 BNC antenna with a new more robust whip fitted to the spring/loading coil. Because the weight of the whip makes the spring bend over it is encased in a piece of plastic electrical conduit which is Araldited to the base of the telescopic whip. This fits into the base section of conduit using one of the famous fragile jointing pieces. A female BNC plugs into the BNC base of the antenna, with the coax and a 19in pigtail counterpoise. This gave a perfect 1:1 SWR at 145MHz when tested at home using my antenna analyzer. It fits nicely in the rucksack with the telescopic whip sticking up above my head, the ultimate fashion accessory for the keen WOTAphile.

The radio was the Kenwood TH-D72 stuck on my belt. The headset I first tried on Carrock Fell proved itself once again, both in helping me to hear the other stations in the howling gale and in keeping the wind noise out of my audio. Regular readers can probably detect a trend here. I think the Kenwood is finally coming into its own as my APRS radio of choice.

I called CQ WOTA a couple of times, with no replies! Was this going to be a failed activation? Eventually to my great relief Mark MM1MPB came back. He gave me only a 5 by 5, which I improved to a 5 by 9 by walking a short way to the other side of the summit. I was concerned that perhaps something was wrong with the antenna so I swapped to the Nagoya NA-701 short dual band flexy-whip and Mark gave me only 5 by 3 so the 5/8 seemed to be doing its stuff. Dodd is quite a hemmed-in summit and although I could see across the Solway to Scotland it's possible that the path to Annan was blocked by the Ullock Pike ridge and the northern flanks of Skiddaw.

A few more calls and I was pleased to be answered by Colin G4UXH in Milnthorpe who had noticed the website spot placed by Mark, and then Steve M0IGG from Walney Island. Both stations were beyond the southern boundary of the Lake District and so at a fair distance. Clearly I was getting out, just not many people were listening. I also worked M6BDV/P on Little Mell Fell for a summit to summit contact, who confused me at first by using the call MW6... his home area being Wales. But that was it. None of the Workington mob or the Penrith crew. I guess everyone was WOTAed out after all the activations over the weekend.

I didn't even see another person on the summit, which is quite unusual. Not that I minded that at all, in fact I always prefer to have a summit to myself than have hordes of people wondering what I am doing.

The views as always from Dodd on a clear day were stunning. But it was damn cold no thanks to that icy wind, so I was pleased to pack up and head back down to the car again. The BMW had gone by the time I returned. How it came to be there with its keys tossed in the undergrowth will probably forever remain a mystery.

High Pike [LDW-107] and Carrock Fell [LDW-105]

Sometimes conditions on the fell-tops are not what you expect when you leave home. Yesterday, having no desire to watch the big event in London, I decided to have a big event of my own, namely to activate two of the Northern Fells for Wainwrights On The Air (WOTA). Although the weather was a little hazy there had been several sunny days and I anticipated two leisurely activations lazing in the grass and basking in the sun beside my guyed WOTA Pole, perhaps even some DX due to atmospheric conditions. I did notice a chilly breeze as I went out to the car, so I went back and got an extra fleece. That turned out to be a good move.

It was about 45 minutes drive to the parking spot at Caldbeck Common. I set off on a circuitous but easy climb up to High Pike, the first summit, working Jimmy on Blencathra who was using a special Wedding call MR3EYP/P on the way. No getting away completely from thoughts of the big event in London.

Half way up I noticed the wind was getting stronger and chillier. The extra fleece was quickly donned, and I worked another activator with a Royal call, MR1EYO/P on Red Screes. By the time I reached the summit I felt conditions were such that I didn't want to stay long up there. After a contact with Bill G4WSB/P on Grasmoor whose voice was at times unintelligible due to wind getting into the mic of his Quansheng, I walked down from the summit in search of a slightly less windy spot to eat my packed lunch.

Whilst eating my lunch I weakly heard Derek 2E0MIX/P on Maiden Moor but I didn't dare nip up to the top to make a contact in case my rucksack and other things blew away. When I did return to the summit I found the wind was blowing icy rain into my face. I didn't have any enthusiasm for putting the WOTA Pole up as I didn't intend staying there long enough for the effort to be worthwhile. I also didn't want to get the non-waterproof Kenwood TH-D72 - which I'd taken after realizing the limitations of the receiver of the VX-8R - wet. So I sat on the stone bench near the wind break on the summit and using the 8in. helical rubber duck rapidly worked 7 of the 'usual suspects', contest-style, then stuffed the Kenwood in the rucksack and set off on my way to the next summit.

Carrock Fell is is a rocky summit with a big cairn, overlooking a valley. By the time I got there the rain had stopped and the wind had dropped a bit and seemed less cold. There were numerous large rocks scattered about making inviting seats. I decided to put up the WOTA Pole. First, I had a fight untangling the guys, which had knotted themselves together. Then, while pulling up the antenna using the third guy, doing my trick of using my walking stick as a bottom section for extra height, there was a crack and the antenna fell back on the ground. The jointing piece between the lower two sections of plastic tube had cracked. Arrgh!

So I was forced once again to do the activation using the 8in. helical rubber duck. However one piece of equipment favourably surprised me. Well, two, really. I began to get used to the Kenwood TH-D72 and felt that perhaps it is a viable alternative to the VX-8GR to use on activations. I received several APRS messages while I was up in the hills and found it easy to read and reply to them. Before I set off I used ?APRSO to load APRS objects for the two summits into the radio which I used to help navigation and check proximity. Very useful, though having to page forward a couple of times is less convenient than the VX-8's all in one view.

I'm still not convinced that the Kenwood's snazzy metallic grey paint and plasticky casing isn't going to start showing marks from the rough and tumble of use up in the mountains. And the radio does sometimes do things I don't understand, like beep and do nothing when I press the PTT, or beep and mute the audio of the station I'm listening to until I press the PTT again. I think this may be something to do with the APRS functions but it confuses me. The battery endurance doesn't seem to be as good as the Yaesu either. But I'm learning to love it.

This was also the first time I could try out a headset for the Kenwood that I'd bought for £3.99 on eBay. The price, which included shipping from Hong Kong, was so low I doubted that it could be any good. But it was also cheap enough to be worth a gamble. It turned out to be the ideal accessory for operating from windy hilltops. The microphone has a foam muffler and even with my head turned so that wind was blowing on to the mic stations reported that there was only very slight wind noise, not enough to interfere with copy. With my head turned away there was no wind noise at all. Experienced activators will know just how hard it is, when it is windy, to find a position that keeps the wind out of the mic on the front of the radio.

Despite the unexpectedly nasty weather I had a nice walk and two successful activations. I may have one last try with the WOTA Pole. I will superglue the cracked jointing piece and then try reinforcing them with nylon cable ties. If that doesn't help then I must give up the idea or accept that it will only work with longer tubes and only one joining section.

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.

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.

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.

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.

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.