Foxed

My FoxTrak APRS tracker board is now installed in a plastic case, together with 4 x AA NiMH cells which provide near enough 5V to power both the tracker and the GPS. Two mini-DIN sockets on the side of the case allow connection to a PS/2 GPS or PC for configuration, and to the radio. Now I just have to make up interface cables to my radios and install the top half of the case after drilling it and installing the charger socket for the battery.

I purchased a GlobalSat BR-355 PS/2 GPS receiver on eBay and it works very well indeed with the FoxTrak, much better than the GPS in the Yaesu VX-8GR. It gets a fix within a couple of minutes when it is sitting on the shack window sill, unlike the VX-8GR which often never finds its position indoors at all, and the position remains rock steady unlike the Yaesu which tends to wander about.

I wanted to make a cable to use the tracker with my Motorola GP-300 hand-held. However I found that the jack plugs you can buy from component suppliers have too wide a body and can't plug all the way in to the sockets on the top of the radio, which are a bit recessed. It appears that you need to use a proper moulded plug with the two pins. A cable for the Motorola GP-300 is available on eBay, so I'm waiting for one to arrive.

I was luckier with the old Kenwood TH-205E. The sockets for external mic, PTT and speaker are flush with the top of the case and the cable I made up using separate plugs works fine. Lacking a deviation meter I adjusted the audio output so the braaps sounded as loud as those from other APRS stations.

However, the TH-205E is a bit big and heavy for portable use, especially as it has a high capacity Ni-Cad battery pack (the original being as dead as a dodo.) I had expected the cable to work just as well with the little TH-F7E, because the Kenwood speaker-mic I have works with both radios. But although PTT works on the smaller Kenwood there is virtually no audio. I have to turn the audio up to maximum on the FoxTrak to get enough signal to be decoded by my gateway, and the deviation is still too low.

I am completely foxed by this problem. The only thing I can think of is that it is something to do with using two separate plugs and not the proper moulded two-pin connector used by the speaker-mic. Perhaps, as with the Motorola, the wide body of the plugs is preventing them from going far enough in to disconnect the internal microphone, which is shorting out the audio. Unfortunately the only way to prove this hypothesis would be to buy a cheap Kenwood speaker-mic or programming cable on eBay and cut the cable off. It's a bit of a gamble, as I don't know for sure if that's the solution, and the cables in some of those cheap mics from China are very poorly screened so I could end up with an RF-induced problem.

Kenwood filter fault fix

As the owner of a Kenwood TM-D710 I was interested to see that Anastasios, SV8YM, has developed a mod to fix the problem of the failing IF filters which causes these radios to go deaf after a couple of years. As explained in admirable detail in his original article describing the problem, it is caused by electromigration due to the fact that Kenwood omitted DC blocking capacitors on the input and output of the ceramic filters. This issue affects the TS2000 as well.

As you can see from Anastasios' excellent photographs, the mod involves cutting some tiny circuit board tracks, bridging between pairs of them with wire, then soldering 0.1uF SMD capacitors between the bridge and the filter input. The TM-D710 has two receivers, each with two filters (one for wide FM and one for narrow FM) each of which has both an input and an output that needs to be treated. So that is 16 tracks that need to be cut and 8 tiny capacitors inserted. I'm afraid working with these tiny components is beyond me, which is a shame as it is now, while my Kenwood is still only a few months old, that it needs to be treated.

Thanks to SV8YM for sharing the details of the modification.

Xastir update is for geeks

Version 2.0 of Xastir, the open source APRS client, has just been released. The new version now supports OpenStreetMap mapping, the same as is used by APRSISCE. I was interested to see that the project web page claims it runs on Linux/FreeBSD/Solaris/MacOSX/Windows so I thought I would try it out on my shack PC which runs Windows. I was puzzled that there was only one download file instead of different versions for each platform, but thought that perhaps they had recoded it as a Java application. I downloaded the .tar.gz file. opened it in BitZipper and found a load of source code files but no .EXE.

There is a file called readme.W32 which contains a lengthy and complex explanation of how to install the program under Windows which involves compiling it yourself using free software development tools. I seem to recall trying this once with an earlier version and failing. Most other developers of popular free software ham radio apps, such as Fldigi, WSJT and WSPR, now produce ready to run compiled versions for Linux, Windows and any other platform their program runs on. Why can't Xastir's developers do this? Most APRS enthusiasts don't possess a PhD in computing so it's unrealistic to expect them to do it.

Fraternity?

Over the last few days a North American ham has been operating a beacon at the top end of the 30m band on the frequency that has been used for many years for HF APRS. At times this has made HF APRS operation impossible. After some difficulty, due to the fact that the beacon operator's contact information was incorrect, someone managed to get in touch with him to point out the problems he was causing and ask politely if he would move the beacon. This is part of the reply that was received, copied verbatim from an APRS mailing list:

"Last week I  moved the beacon when  some other hams we're bitching at me  about 'their'  all important!!!   ham activity......   PSK,  RTTY   what ever!!! . 

I move AGAIN then another cry baby bunch CRIES about 'THEIR'  ALL IMPORTANT    activities  like weak signal CW QRRS CW  whatever!

We have to SHARE the frequencies   I will think about the  QSY  .....  if I get Bitching from so other ham 'group' like the DX cluster folks who are  'DXing'  fish in a BARREL for some  ALL IMPORTANT  'certificate'     What am I to do???  I am an experimenter /builder  when do I get to use a frequency????????

WHY is 'APRS'  more important than MY activity?  I look in the regs and I  see NOTHING about one  ham activity has  priority over another!"

I have left out the individual's details as I don't want to start a personal attack that could be counterproductive by leading him to entrench his position. But whatever happened to good manners, politeness and consideration for one's fellow amateur? When, as a young teenager, I first began listening on the amateur bands, I used to be impressed by the politeness and courtesy of the conversations I heard. No longer is amateur radio a gentleman's hobby.

This OM is quite correct that we have to share the frequencies. It is a common courtesy that if a frequency is in use then you don't use it, even if you have a net that has been meeting on that frequency every day since Marconi invented the spark transmitter.

But in the digital parts of the bands which can be used for more than conversations between two or more people, checking whether a frequency is in use may involve more than just sending "QRL?" or listening for a couple of minutes. Activities like APRS, packet radio, Winlink and so on are effectively nets that operate 24/7. If you don't hear anything for a while that may just be because propagation isn't sending anything your way at the moment.

This is how Chris, G4HYG prepared to select the frequency to use for APRS over PSK. He recently wrote: "Before I released the HF version of APRS Messenger I spent some time checking  various frequencies on the 30m band. I found that the section from the 300 bd APRS frequency to the band edge appeared to be clear. I then started a period of monitoring the band from 10.1494 to 10.150 on a receiver with a digital mode program running with a very slow waterfall to catch anything I heard. This ran for a month from mid January to mid February." It's a pity the developer of the ROS digital mode that has caused so much disruption to other established activities could not have been as thorough and considerate in selecting operational frequencies.

To those who will trot out the response that activities like APRS have no more right to use a particular frequency than anything else I would say first of all that some types of activity need a specific frequency where other users can find it. It isn't a matter of one activity being more important than another. If you had to hunt to find what frequency everyone is using today, some types of worldwide net operation would not be possible. In any case, a frequency that was clear in, say, North America might well be occupied in Europe. Allowing legitimate activities sole use of an established frequency by gentleman's agreement is the only option. There is still plenty of room for other activities including ad-hoc beacons.

In activities like APRS, many dozens of stations all use the same frequency, making this a very efficient use of bandwidth. If users are driven off these frequencies or prevented from using these modes the result would be even less space left for other activities.

What people who object to this argument really mean is "I don't have any interest in that mode and I don't give a fig about those who do." Is ham radio a fraternity? Yes, we are like a family of brothers who are forever breaking each other's toys and beating the shit out of one another.

Cross Country Wireless SDR update

Cross Country Wireless has just announced an updated version 2 of its low cost SDR Receiver. The new version has an RF preamplifier using a power MOSFET after the RF bandpass filter which is claimed to improve sensitivity - which was a criticism of the earlier version - and reduce local oscillator output at the antenna port.

The designer Chris, G4HYG, claims that the receiver will now display a CW carrier at a level of -135 dBm on the waterfall of SDR-Radio using a 48 kHz sound card. The level of the local oscillator at the antenna port is now specified as -65 dBm, though a more typical measurement is -70 dBm. This should make it an ideal choice as a panadapter for radios such as the Elecraft K3. In fact, Chris recently stated that most orders for the receiver have been for use as panadapters, in conjunction with a sound card and suitable software such as PowerSDR-IF.

The cost of the standard SDR is £49.95. For panadapter use you will need a custom crystal for your radio's IF which increases the price to £59.95. The SDR has two (switched) local oscillators so the other one could be specified to cover 40m or 30m for use as a conventional receiver. It's also available as a built and tested board for assembly into your own case (at a significant saving.) If you built a USB sound device into the same box then it would be rather neat.