Monday, January 31, 2011

Packet lives!

I thought packet radio was all but dead. Yesterday I heard Richard MM1BHO mention that there was a packet node in Scotland on 70cm at the same location as the GB3LA repeater which is a monstrous signal here. I asked Richard to tell me the frequency so I could have a listen. I wasn't optimistic about hearing anything as 70cm has always seemed a bit of a dead loss for me. I had to wait a while to hear anything, and when I did, I found the packet signal was 20dB over S9 which is the strongest signal I've ever heard on 70!

I then spent a couple of hours trying to sort out a way of receiving the packet. TrueTTY seemed like a good choice. It decoded the packets and displayed them on its screen. But I couldn't find any software that would work with its virtual TNC.

I also tried AGW Packet Engine in sound card mode. That, too, decoded packets, so I got the AGW Terminal software as well. But I could not transmit. The software keyed the PTT when it was supposed to, but there was no audio modulation.

Finally I bit the bullet, shut down the APRS gateway and put the Kenwood D710 into packet mode. I then set up AGWPE to talk with the Kenwood's TNC. That worked, and I was able to connect to the node whose call is GB7WD. I was wondering what to do next when Clive GM4FZH connected to me and I had my first chat over packet radio since the mid-1980s!

I'm afraid after all that time I have forgotten just about anything I knew about packet radio so I'm still pretty clueless as to what to do. I don't know how to set up a mailbox, or even where to set one up. There seems to be a shortage of material on the interweb aimed at packet newbies (or oldies like me where the onset of Alzheimer's has erased any memory of what we once knew!)

I think packet radio is something I will enjoy playing with again. I went back to AGWPE soundcard mode and found that the reason I was not getting any audio was because although the software says it uses the left channel which online references claim is the tip of the stereo jack, it was actually present on the ring. After resoldering the connector on the audio cable I was able to transmit packets as well as receive them, and G4ILO is now listening on the GB7WD frequency on the A side of my TM-D710 while my 2m APRS gateway is using the B side. There are just so many things to do in this hobby!

Friday, January 28, 2011

Sporadic-E on 6m

The first bit of live data I received from my APRS VHF propagation alert reflector was a warning of a possible Sporadic-E opening on six metres. I was rather surprised that there was Sporadic-E this early in the year, but I went to the DX Sherlock website and sure enough contacts had been reported between a station even further north than here and one in the Czech Republic. I then clicked on the map to see the actual contact details and was surprised to find they were WSPR spots!

I went to the WSPR website and sure enough the same signals were shown. I decided to fire up WSPR on 6m myself but by then the OK station had gone and no new spots appeared from anywhere.

I have been, and still am, somewhat sceptical of the value of WSPR in showing VHF Sporadic-E propagation. One of the characteristics of Sporadic-E, particularly at the start and end of the season or on the higher frequencies like 2m is that it is very fleeting. A signal can be there for one minute, literally, and gone the next. On the other hand, signals can be really strong when reflected by Sporadic-E. WSPR is designed for detecting weak signals under steady propagation conditions and uses a 2 minute transmit cycle during which the data is transmitted very slowly. It seems to me that what you want to detect Sporadic-E is a mode with short transmit cycles where the data is transmitted quickly, perhaps something more akin to the modes used for meteor-scatter. I wonder if K1JT could come up with something?

Nevertheless I am very interested in anything that helps to detect VHF openings that might otherwise go undetected. I plan on WSPRing more on the 6m band, as long as there are others doing likewise so there is a chance of being received!

VHF propagation alerts over APRS

I have just set up an ANSRVR notification group (the APRS equivalent of an email reflector) called CDGVHF. The purpose of the group is to alert interested subscribers in the Cumbria, Dumfries and Galloway area to possible openings on the 6m, 4m, 2m and 70cm bands.

The APRS alerts make use of the email alert service of DX Sherlock which sends alerts of possible band openings customized to the subscriber's location, based on DX Cluster spots and other reverse beacon information. I have set up a subscription to send alerts of possible band openings workable from the IO84 grid locator to a special email address on the G4ILO's Shack web server. Using a feature of the cPanel web hosting, the email is "piped" to a script written by me in the PHP language. This extracts the subject header of the email which contains a succinct description of the alert, shortens it as much as possible and then sends it as a message to the CDGVHF ANSRVR group, which then forwards it to all interested subscribers.

Why is this better than just subscribing directly to receive the alert emails? Because I can now receive the alerts on my APRS-equipped hand-held, which should greatly reduce the chance of missing a good band opening because I wasn't in the shack at the right moment.

Thursday, January 27, 2011

60m WSPR using 500mW QRP

I have been beaconing WSPR using 500mW all day today. The KAT3 didn't want to repeat its trick of matching my multi-band dipole so the best SWR I could manage was about 1.8:1. I don't know how much of the 500mW ended up warming up the ATU or the coaxial feeder.

This is a shot of the WSPR propagation map taken just before 1800z today. As you can see, the 500mW is getting out pretty well. I think I have been received by all the G stations that have been monitoring at some time during the day, and a few others. And it was nice to see fellow bloggers Paul PC4T and Bas PE4BAS monitoring even though they can't transmit on 60m, and better still spotting me!

Just after I posted this, my 500mW was also spotted by LA3JJ!

Wednesday, January 26, 2011

First emissions on 60m

On looking through the mail at lunch time I saw that I had received a letter from Ofcom. My NoV permitting me to operate on the 60m experimental band had arrived!

Until now I hadn't been bothered about operating on 60m because I couldn't see how I could possibly find room for an antenna for that band. However a couple of weeks ago I heard someone activating a SOTA summit in the Lake District on 60m and was frustrated that I could not reply to them. So I decided to put in an application for permission to operate and here I am.

I don't have an antenna that is resonant on 60m so I tried tuning up my multiband dipole using the K3 auto ATU. After a lot of persuasion it managed to find an acceptable match on the higher frequency channels but it gave up on the lower ones. So I should be able to manage some activity on the new band.

Fortunately, the channel allocated for beacon and WSPR use is one of the ones I was able to match. And today just happened to be a 60m WSPR activity day. So I fired up the WSPR software and beaconed on 60m using 2 watts, increasing to 5 watts in the evening when propagation went long and most of the traces faded out. The 5 watts did me no good at at all, but my 2 watt signal was heard by 7 different G stations all around 400km distance from me plus F/G6AIG at 760km. I received 6 different G stations including G4ZFQ at 458km running 20mW, plus OZ1PIF (my best DX at 984km) and LA3JJ.

Tomorrow is QRP day on 60m when everyone is supposed to run 500mW or less. I have not decided yet how little power I will run but I will be WSPRing on 60m all day. Hopefully there will be a few more people who manage to spot me.

Round the back way

Back in the early QRP days of Elecraft, there were some K2 owners who were such CW diehards they were uncomfortable with having a radio that possessed a microphone socket. One or two of them described to the Elecraft email reflector how they had blanked off the offending socket. Despite the evidence in the picture on the right, I have not joined this fraternity. I have simply started using the rear microphone and PTT connector on my K3. I have thought for some time that the front panel connector is an accident waiting to happen, and I finally decided to make the move before it did. (And before anyone comments about the dust in the photo let me just say that one of the few benefits of deteriorating eyesight as you get older is that you don't notice it!)

Front panel microphone sockets are pretty much the norm in ham radios. However in most radios they are secured directly to the metal front panel or, in the case of radios with a plastic fascia to the metal chassis behind it, using a locking nut which tightens the chassis against the ring cast into the socket so that it is rock solid. You could tug at the microphone cable all you want or bash the connector with a hammer and you would be unlikely to cause any damage to the radio itself.

In the K3, the microphone connector comes soldered to the front panel board. There is no possibility of securing it to the metal front panel. The ring that would normally sit on the outside of the mounting hole actually slips through the hole in the front panel so all the rigidity is provided by the PCB. The front panel hole limits movement up and down or side to side to a certain extent. But it does not provide any protection from movements fore and aft. I wonder about the effects of constant small side to side movements on the soldered joints connecting the pins to the board. And I feel sure that if I accidentally leant on the microphone plug, supporting my weight as I tried to make some connection round the back, I could damage the front panel PCB by snapping the microphone socket right off.

As the outer body of the microphone connector is not physically attached to the radio itself it is not electrically grounded. Whilst installing the K144XV transverter board I noticed that grounding is provided by a piece of bare wire that loops round the threaded part of the connector and is soldered to the front panel board. This may have been a modification that I did myself when I assembed my K3 three years ago. What this wire loop does not do is prevent the outer metal part of the microphone connector from turning relative to the insulated centre bearing the 8 pins that are soldered to the PCB.

Because of the perceived risk of damaging the front panel board by accidentally putting my weight on the microphone plug I have been in the habit of disconnecting the microphone whenever I need to lean over the K3 to grope round the back. So the microphone connector has been on and off rather a lot. Recently I observed a tendency for nothing to happen when I pressed the PTT on my desk mic after reconnection. It then became apparent that the outer metal part of the plug has become slightly loose and can be twisted several degrees relative to the centre. I'm pretty sure this is due to the plug body not being secured to the chassis of the radio so there is nothing to take the strain of tightening and untightening the microphone plug. Hence my decision to give up using the front panel socket and move round to the back before the problem got any worse.

My shack is very cramped so I had shortened the cable on my Heil desk mic to eliminate unnecessary length when plugged in to the front of the K3. Consequently it would not reach round to the back. Rather than rewire the microphone I decided to make an extension cable using a line 8-pin socket, retaining the option of using the front connector if I want. I purchased the line connector quite inexpensively from an eBay seller (where else?)

These connectors are much easier to work with than the mini-DIN connectors I have recently been using rather a lot. The pin numbers are clearly visible, but it's a good job I checked: in the connector I had the pins had been installed in the metal socket offset by one pin position so pin 1 was labelled pin 7 etc! This could easily have been confusing and so my brain cells got a bit more exercise than expected making sure I got the connections right.

I changed the microphone configuration in the menu to use the rear mic socket and so my microphone is now plugged in round the back. It would be interesting to know whether any other K3 users have had problems with this front panel socket. Once, I would have posted about it on the Elecraft email reflector, but that would only result in several replies from kool-aid drinkers saying that it hasn't happened to them so it must be my fault.

Monday, January 24, 2011

EchoLink node

A week or so ago my application to operate a part time attended EchoLink node on the 2m band was granted. I didn't receive any notification of this, I just happened to check the relevant page of the RSGB Data Communications Committee website and noticed that my entry had turned black and an expiry date had been added.

G4ILO-L is EchoLink node number 3098 and operates on 145.2125MHz with a CTCSS Tone of 77.0Hz. As stated the authorization only allows the node to operate when I am on the premises. It uses the non-APRS side of my Kenwood TM-D710 so in practise it will also only operate when I don't want to operate on 2 metres myself. Therefore it is more likely to be on during the evening UK time than during the day.

The license only allows me to use 5W ERP. Due to my location in the RF black hole of Cockermouth the range will only be a few miles so the number of stations able to access it can probably be counted on the fingers of one hand. Most of the time I will be monitoring the node myself on one of my handhelds so if you call me after connecting there is a good chance I will reply.

I do intend to post a page on my website explaining to other stations in the area how to use it if they want to, but at the moment the number of things to do exceed the available time.

I have developed a script to post the status of the node to the APRS network so an easy way to see whether my node is running or not would be to look up EL-3098 at

Friday, January 21, 2011

WSPRing on 80

A blog post by Roger, G3XBM, about how far he was able to be received running 5mW of WSPR on 80m using a lash-up antenna prompted me to give QRPP WSPR a try. But before I could start, I needed to make an attenuator. The lowest power my K3 or K2 will go down to is 100mW, but not with very much accuracy. I decided to make a 20dB attenuator which would divide my power by 100, so I could run 1W and get 10mW output.

There are numerous websites that will design an attenuator for you given the working impedance and amount of attenuation required. I was not looking for precision - I would be surprised if the output of either of my radios was within 10% of the selected power anyway - and moreover I wanted to build it now using parts from my junk box not have to send off for some exact values and wait for several days for them to arrive.  My attenuator was built as shown above and gave a 1.2:1 SWR over the HF range which was good enough for my purposes.

I started yesterday evening running 10mW on 80m into my end loaded attic dipole. I received no spots at all initially. I was puzzled as to why I could hear the WSPR audio using the K3 monitor even though the extension speakers I use with the K3 were switched off. I was about to compose an email to Elecraft enquiring whether the last firmware update had the effect of routing the monitor audio to the internal speaker even when an external speaker is connected when I realized the sound was coming from the computer speakers! Windows had decided to renumber the sound cards since I last used WSPR and although the receive channel was still the same and spots were being decoded the transmit audio wasn't going to the radio. Doh!

Some time after I began transmitting I received a couple of spots from G3XLW 478km away in the south of the country. But that was all. I decided to leave it running overnight and received spots from David off and on throughout the night. These were augmented in the morning after 0800z by three spots from M0DDT at a distance of 355km to the south east. Not as impressive as Roger's results. I guess my attic dipole, being very low for an 80m antenna, is a cloud-warmer and sends most of the RF straight up. Roger was loading the feeder of his 10m halo which doesn't sound like much of an 80m antenna but in effect he had a top loaded vertical which probably has more lower angle radiation. That's my theory, anyway.

It was an interesting test and I shall try very low power WSPR again on other bands. However I don't agree with the extremist view held in some circles that people should only use WSPR with such low powers. It's certainly interesting to discover if you can get to the end of the street on 10uW but higher powers of a few watts will reveal propagation to places lower powers won't, information that is likely to be more useful when applied to making contacts using other modes.

Thursday, January 20, 2011

NASA seeks help tracking satellite

NASA has asked amateur radio operators for help to determine if a recently launched satellite is operating. The NanoSail-D satellite was ejected automatically from the Fast Affordable Scientific and Technology Satellite, FASTSAT on Wednesday, January 19. NASA needs reports of the beacon telemetry to determine if it is operating correctly. The beacon signal is on 437.270MHz using standard AX.25 packet so APRS and packet radio operators with 70cm capability should be able to receive it.

Predictions for the satellite can be found here. Reception reports can be submitted here. Full text of the NASA press release here.

Wednesday, January 19, 2011


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.

Tuesday, January 18, 2011

Connector conundrum

What is one supposed to do with the BNC connector pictured right?

I ordered 5x Crimp On BNC Plugs from eBay, expecting to get plugs with a narrow body and separate small piece of tube that you use to crimp the braid of the cable to the body of the plug. What I actually got was these, which I already had a couple of and didn't know how to use. The only way I can see that you could use these is to crimp the large diameter barrel on to the braid itself, but with nothing but the nylon insulation beneath it you are not going to get a good contact. I think they are useless, though I did make a QRPP dummy load from one of the originals as two 1/4W 100 ohm resistors in parallel just fit inside the body of the plug and you can solder the ground ends to the outer.

I guess soldering the braid is the answer, but that isn't what I bought crimp on plugs for and it isn't going to make a very neat job.

Saturday, January 15, 2011

K144XV comments

The K144XV eventually turned up late on Thursday afternoon. After the board modifications had been performed, installing the transverter module was easy following Elecraft's exemplary instructions. I had to remove the KIO3 module in order to remove the KXV3 transverter module and replace it with the KXV3A, which has a couple of additional connectors for the internal transverter, then replace the KIO3. I also had to replace the side panel of the K3 with one that has some extra holes for securing the transverter. The stiffener that runs across the top of the case is also replaced by one with a cutout where it passes over the K144XV.

Due to the lateness of the hour I was a bit tired and also focussed on getting the job finished so the shack could be restored to normality so I never even thought about taking some pictures. The module comes as a complete screened box not a bare board as shown in some of the pictures on the Elecraft website. It is quite a little beauty and the way it all fits into the K3 is a work of art.

Although described as a 10W module the instruction manual states that you should get at least 9W with 1.0mW input to the transverter. I actually got about 11W so the power output comfortably exceeded spec. At my noisy location I can't make any meaningful observation about sensitivity - any half decent 2m radio will be sensitive enough. But I did notice that S meter readings are extremely low. I see no movement at all on a clear frequency despite the noisy location and a repeater that lights all the signal strength bars of my TM-D710 registered just S4 on the K3. I never take any notice of S meters anyway so I'm not unduly bothered. The amplifier "brick" I will use with this has its own built-in preamp which will boost S meter readings if I want.

The 2m amplifier I have was designed to be driven by an FT-817 so it only requires an input of 5W. I found that I needed to reduce the drive to the transverter to a mere 0.15mW to achieve this level of output. I don't know how accurate the low level output power settings of the K3 are but the relationship between 28MHz drive in and power out is definitely not linear. However the signal on SSB sounded pretty clean when monitored on the FT-817.

The calibration of the transverter local oscillator is done using software, not by trying to tweak a trimmer capacitor by a fraction of a hair's breadth, which is a blessing. There are two local oscillators in the transverter to provide coverage of the full US 2m band (144 - 148MHz) using the same 28MHz - 30MHz range (interestingly the top 2MHz is not disabled in European rigs.) The transverter module is calibrated at the factory and you have to enter the calibration values into the K3 using the configuration menu. I checked the result using my FC-1 frequency counter and also my FT-817 and it appeared to be accurate to within 100Hz which is about as good as I can get. Later I listened on the GB3VHF beacon frequency and waited for the beacon to come out of the noise. I believe this beacon's frequency is GPS locked. The frequency appeared to be out by 120Hz so I was able to adjust the calibration value and get it spot on.

The signal to noise ratio on a weak FM signal is definitely better on the K3 than with my other 2m rigs but I don't see the K144XV as being the solution for people whose primary interest 2m FM. One reason is that a 2m mobile rig is cheaper and allows you to monitor and work 2m FM at the same time as using your K3 for something else. Another is that the K3 doesn't really handle channelized operation very well. The memory system has improved considerably since the early days but using the VFO to scan through memories rather than a click stop rotary control doesn't work for me, especially due to the laggy response of the K3 to the turning of the knob.

But I think the K144XV is an excellent option if you want to work 2m DX. The receiver sounds quiet and clean and having all the QRM fighting and weak signal detecting tools of the K3 available on 144MHz is a real bonus. Now I just have to wait for some 2m SSB activity to try it out!

Thursday, January 13, 2011

K3 mod fun

Today I have been waiting for Parcel Farce to deliver a K144XV internal 2m transverter board for my K3. I hate doing modifications to the K3. First there is the hassle of disconnecting all the cables that are plugged in the back. I have to disconnect practically everything in the shack in order to remove the shelf above the K3 so I can see what I am doing.

I also dislike making modifications to the K3 itself. It makes me nervous thinking of the cost and expense if I mess something up and it doesn't work. I'm starting to think that if I want to stick with the K3 it would be better to sell this 3 year old one and get a new current model. Because there have been so many modifications now since my serial number 222 was produced. I haven't done many of the mods because I don't think they make a worthwhile difference or because they involve obtaining an exchange board from Elecraft and the cost of doing this including shipping, VAT and tax collection fee is more than it is worth. But the internal 2m module seemed in the end to be the best solution for providing a capability for 144MHz SSB, even though it involved exchanging my KXV3 transverter interface board for a KXV3A.

In order to install the K144XV it is necessary on older K3s like mine to mount a socket on the main board to provide power. This involves removing the bottom panel of the rig. I thought that while I was doing that I would do another mod to increase the IF output which would be necessary should I ever want to use a P3 panadapter with the rig. The mod involves changing one resistor, oddly specified at 13K. An enquiry on the Elecraft reflector about whether the value was that critical resulted in the kind offer from Ian GM3SEK to send me a couple of SMT resistors so I could do the mod. Without Ian's help I would have had to leave the mod until I got a P3 and Elecraft sent the replacement part because SMT resistors aren't something you can buy from Maplin in quantities of one or two off.

I had shied away from doing mods involving SMT parts before but I found that it wasn't too hard. However I did need to use a high magnification lens in my head-mounted visor. I was initially alarmed to see that the resistor I had to change wasn't one of the fairly big SMT resistors that are normally used in kits using these type of parts, it was a really tiny one. I used two soldering irons, one at each side, and then flicked the resistor off. After cleaning the pads with a bit of solder wick I then took one of the replacements using a trimming tool with a bit of Blu-Tack on the end and held it in place while I took a blob of solder on the end of my smallest bit and tacked one side of the resistor into place. Then I did the same to the other side. Job done.

Although the high magnification makes it possible to see the tiny parts, it can't do anything about shaky hands. My hands seemed fairly steady this morning but it is a different picture through a high magnification lens and you don't need to move far to shift the component out of its precise spot, which of course I did. I decided this is no job to be fussy about. The resistor was slightly skew-whiff, but it was attached to the board and my ohm meter said everything was OK. Perhaps I could get a job working for MFJ. :)

The package from Elecraft still hadn't arrived so I decided to pull up the instructions for installing the K144XV from Elecraft's website to see what was involved. As I mentioned, I needed to install a terminal to provide 12V to the transverter module. This is a bit of a kludge as the K144XV wasn't even a planned option at the time my K3 was made so there isn't a proper place for this terminal. You have to solder it in using a "via" that wasn't actually designed for this use. Unfortunately that via had been used by one of the leads of a wire-ended capacitor used in another mod to improve the low frequency audio response.

The instructions mention this possibility and suggest an alternative via. However that via was obscured by the components used to perform yet another mod, this time the hardware AGC modification. Lacking the confidence to remove and replace SMT parts I had used wire ended components to do this mod. There was no alternative but to remove the mod and do the SMT version. Elecraft had provided both types of components and fortunately I hadn't lost the SMT ones. However they had not provided any spares and I was conscious that one false move sending a resistor pinging off to oblivion would result in a K3 I would be unable to use until I could find a replacement. That didn't help the shaking hands one bit!

Fortunately it all went well, with the results shown in the picture. (The resistors I had to replace are the ones marked 333.) So that's done. But still no transverter. Where the hell are you, Parcel Farce?

Tuesday, January 11, 2011


Charles M0OXO laments the fact that England is 334th in the list of the most wanted 338 DXCC entities, in other words the fifth least wanted. Isn't it a sad waste of a hobby not to mention the vast sums of money people spend on equipment and antennas if the main interest in making a contact is just to be able to tick off a new country? I guess that's why I find DXing and DX blogs boring. I'd rather read about what people are building, new things that they are experimenting with or how far (even if it isn't all that far) someone manages to work with a peanut whistle.

Monday, January 10, 2011

Automatic Voice Relay System

One of the reasons why I have not been an enthusiast of the D-Star system is that it creates a separate class of activity incompatible with existing voice modes just for the dubious benefit (from an amateur point of view) of using digital voice instead of analogue. Using EchoLink, IRLP and APRS we already have a global network that allows one ham to contact another anywhere in the world using ham radio, one that does not require anyone to purchase expensive new equipment from Icom or anyone else. What we have not done is put it together in a way that makes it work seamlessly as a coherent network.

Automatic Voice Relay System (AVRS) is an idea by Bob Bruninga, WB4APR, the inventor of APRS, first published in 2000, to create a system that allows users of EchoLink, IRLP and even D-Star to inter-communicate. APRS provides the location and identification information for the analogue FM EchoLink and IRLP users, something that is already built in to the D-Star system. As is often the case, those who have the great ideas don't always have the skills needed to bring them to fruition, so AVRS remained little more than an idea for ten years.

Now, apparently, a developer has been found who is able and willing to write the software that will enable AVRS version 2 to come into being. You can read more about AVRS here. For seamless one-button operation you will need one of the new generation of APRS-capable radios (Kenwood TM-D710, TH-D72 or Yaesu FTM-350) that are able to QSY to a frequency contained in an APRS packet. Some will argue that if you are going to buy one of those, why not buy a D-Star radio instead? But AVRS capability, being based on APRS, can easily and inexpensively be added to any analogue FM radio. AVRS will not leave analogue FM users out in the cold because their local repeater converted to D-Star, as has happened in some parts of Britain.

One of the interesting aspects of AVRS version 2 is the development of A-Star repeaters. These are analogue FM repeaters with a D-Star gateway that use the D-Star network to link them together. Callsign and location (if known) information is transmitted as a 0.3sec APRS packet burst at the end of each over. A-Star users will appear to D-Star users just like other D-Star users and can easily intercommunicate. A-Star users can initiate a contact with another A-Star or D-Star user just by sending an APRS message starting with A*. A-Star users don't even need to be monitoring a repeater in order to be contactable: they will receive the message as an ordinary APRS message and can QSY to the repeater (with one button press if using one of the radios mentioned above) using the information contained in it.

AVRS looks like a great idea with the potential to bring digital and analogue voice users together. It might even erode some of the analogue vs D-Star conflict.

Saturday, January 08, 2011

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.

Thursday, January 06, 2011

Microlight QRP

Keen followers of SOTA will have read about this on the SOTA Reflector, but during the last couple of months Richard G3CWI has been activating summits using a 30m transceiver powered by a 9V PP3/MN1604 battery. This apparently is in response to a challenge set by another keen SOTA activator: Kjell, LA1KHA (who visited us in October 2009.)

I couldn't find many details of the challenge, so I'm just assuming that it was simply to see how many activations could be made using a radio powered by one of these small batteries. Kjell is believed to be using a Small Wonder labs RockMite but Richard built his own transceiver especially for the challenge. The receiver uses a two-crystal ladder filter at the signal frequency, an NE602 mixer, a low noise AF amplifier and active lowpass filter using CMOS op-amps. The transmitter has a crystal oscillator, bipolar buffer, bipolar amplifier and FET class E PA giving 300mW output and an internal Tick1 keyer.

With this transceiver Richard has now activated 10 summits making more than 100 contacts, still using the original PP3 battery! Having established that a PP3-powered transceiver is adequate for reliable activating Richard is now looking for ultra-lightweight HF antennas to get the weight of his portable station down to the absolute minimum.

I think this is a fascinating challenge and hope that Richard will write up the experience in more detail one day, perhaps in his RadCom Portable column or in the G-QRP Club magazine Sprat. This is really what QRP is all about, reducing the equipment to the bare essentials. It also shows the value of CW as the only mode that allows you to use such simple equipment.

Monday, January 03, 2011

Weather station

As I was not making any progress on other projects for one reason or another I decided to build the Fox Delta WX1 weather station kit that had been sitting in a drawer for the past couple of months. For several years I have had a simple wireless weather station that tells me the outside temperature, humidity and pressure. Since getting into APRS I wanted to be able to put this information on the network. Most of the weather station products I've seen interface with a PC using some proprietary software, which ties you down to a particular operating system. It also typically interfaces with APRS using some proprietary method that works with UI-View but is not supported by APRSISCE. The elegant solution would be a weather station that transmits the weather information as an APRS packet using a low power RF link, which would then be received by my VHF IGate. When I discovered that the WX1 produced 1200baud AFSK audio output and a PTT signal to control an external transceiver to do exactly that it seemed just the solution I was looking for.

Unfortunately the WX1 was no longer for sale from the Fox Delta website. I contacted Dinesh, the proprietor of Fox Delta and he explained that although he still had a couple of boards and most of the parts for the WX1, the kit needed to be redesigned to support the latest 1-Wire anemometer so he had taken it off the market. I told him I didn't want an anemometer. Our garden is so tiny and surrounded by houses, trees and bushes that I would never get an accurate reading anyway. Besides I didn't think Olga would be thrilled to have an anemometer planted in the middle of her flowers. And from what I've read, most of these home weather station anemometers fail after a year or so. So Dinesh agreed to sell me a kit and I had to take up the offer there and then even though it hadn't been something I'd planned on doing right away.

The weather station turned out to be quite easy to build despite the fact that there are no detailed step by step instructions, just a parts list, a schematic diagram and the silk-screened PCB to show you where each component goes. Most of the parts were supplied in individually labelled small polythene bags which helped a lot. I had a nasty moment after I soldered in a crystal X1 and then realized the second crystal on the board was also labelled X1. But the two devices were in a completely different form factor and would not match the outline in the wrong place so there was little chance of a mistake. Amazingly, for something built by me, it worked first time.

I set up the weather station running standalone in our unheated conservatory and I was disappointed to find that the temperature readings were several degrees on the high side. I was also disappointed that the configuration software provided no way to change the display of temperature from Fahrenheit to Celsius. The sensors for temperature, humidity and pressure are all mounted on the board itself. I had thought that I would be able to extend them via a cable so the sensors could be outside and the weather station inside but on closer examination I could see that was not going to be practical.

The temperature sensor chips are actually underneath the LCD display and it appeared that the LCD backlight may have been contributing a bit of local heating. Given that the unit will have to live out of doors, the display will not be particularly useful. In fact, the instructions state that if you want you can take it off to save power. So the problem of high readings and the Fahrenheit display can be resolved simply by removing the LCD, which as it is a standard display panel, can probably be used in another project. I tried it on my EasyPIC5 development board and it displayed some demo text.

The plan is to use the Radiometrix TX1 10mW transmitter module that I recently bought for the 144.800MHz RF link. However to get the weather station on the air quickly I made up a cable to try it with my old Kenwood TH-205E. I put them in the garage to get close to the outside temperature, and one problem quickly reared its head. As with the FoxTrak I found that the PIC-based circuit is extremely vulnerable to RFI. Even 0.5W into a short Nagoya dual band antenna on the Kenwood was enough to cause loud buzzing on the audio and once to lock up in transmit and corrupt the atmospheric pressure calibration. The rather poorly made case provided by Fox Delta offers very little in the way of screening, especially with the aperture for the LCD display. Hopefully the 10mW produced by the Radiometrix module won't necessitate the elaborate screening measures that were required by the FoxTrak.