Unwanted

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.

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.

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.

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.

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.