AO-40 Operation

In the Winter of 2001 I decided to get active on AO-40. I was told that activity was relatively low and the "lid" element had not discovered it yet, they seem to spend their time on the FM LEO satellites instead. With a little research on the web I discovered that all I needed to get active was a downconverter for 2.4GHz and a dish feed, my existing 60cms dish for microwaves was perfectly adequate with a reasonable feed.

I had been active on AO-13 mode L and mode S in the early 1990s using mostly home made equipment. I used to use a 1.4m dish for mode S downlink and mode L uplink and a dual helical feed. The equipment had been from LMW Electronics, the mode L uplink was my old 23cms transverter with a new oscillator board and a dual M57762 amplifier giving 30 Watts, the mode S downlink was also from LMW Electronics, a 13cms receiver converter feeding a 2m-10m converter and driving a TS670, the noise figure was around 1dB. I forget which radio I used for the mode L uplink, maybe my TS711E ? The 70cms side of both of these modes was via a crossed 19ele F9FT yagi to a TS811E with a masthead pre-amplifier.

     

My choice of downconverter was obvious, DB6NT of course, the MKU 24 OSCAR has a noise figure of 0.6dB and more than enough gain so I ordered one. I built a bias-T to supply it with 12V down the co-ax to avoid having to run a separate power cable to it. For a dish feed I had the choice of either making a helical or a patch. I had been active on AO-13 mode S (2.4GHz downlink) back in 1990 using a helical, so I decided to try a patch this time. Unlike a helical, a patch is really only suitable for a relatively small range of dish f/D ratios, however it suited my dish perfectly. I discovered a design by K3TZ and built it in a very short time. This is a close up of the feed, and of the dish.

   

Using my own satellite tracking program, MTrack, for Linux I quickly found the satellite and started to receive signals. Yes it was that easy. Unfortunately my antennas had to be mounted on a temporary tripod and placed onto the balcony every time it was used, my equipment was loaded onto a wheeled IKEA trolley to enable it to be moved into the living room for AO-40 operation. This was also handy for microwaves as I had to use two different windows for operation in different directions. The arrangement of the dish on the balcony, using the U-band uplink, can be seen below.

    

My original downlink was an old Kenwood TS700G, and I used 70cms for uplinking using my Icom IC-706 barefoot (about 20W) into a vertically polarised 13 element yagi. Signals were acceptable and I made a number of QSOs. This picture was taken just after my first AO-40 QSO, the IKEA trolley can clearly be seen.

For Christmas 2001 my wife bought me an Icom IC-910H with 23cms module. A couple of months previously I had bought an SSB Electronics TLA1270-100B, a 100W solid-state PA for 23cms for a very reasonable price. With this combination and a 26 element yagi, I moved up to the L-band uplink and found signals to be much cleaner and of course without LEILA. One rule was that I always used a different radio for the downlink than the uplink after hearing about people frying their downconverters. The downlink receiver was usually mt IC-706, with its microphone disconnected.

This system was in use until my dish was returned to microwave operation when the Rain Scatter season started in May 2002. Once my microwave system had a dedicated 90cms dish, my 60cms dish was returned to full-time AO-40 operation. Some more QSOs were made via AO-40 after the initial period of operation, and the results of all of my AO-40 operation can be seen in my log books, in the Logs section of my web pages.

At one time I had planned to try a 90cms dish on the L-band uplink, using a helical as a feed. I made the helical and tuned it up ready. Unfortunately a combination of the weight of the dish and my mounting system were not able to support the dish at the required elevations and so it was never tested. Quick calculations showed that the signal with the dish would have been comparable or better than my yagi, 3dB being gained by going from linear to circular polarisation alone.

Another idea, more fully realised, was to have two downlink receivers operating simultaneously. This was achieved by building a 6dB resistive splitter and buying an Icom IC-PCR1000 as a second receiver. This worked very well, the role of the second receiver was either to receive telemetry at the same time as I was operating, or to produce a spectrum of the satellite passband to view activity, and see who was being (too) loud, usually me !

As you may be aware, AO-40 is currently dead and attempts are being made to regain control of it. This is extremely sad for all concerned as it was a fine satellite and I had many happy hours of operation working stations through AO-40 when I lived in Switzerland. Unfortunately when I returned to the UK I found that my current location was too poor for AO-40 as the surrounding hills were too high, a problem that didn't occur with AO-13 because of its higher inclination orbit. Therefore I never operated on AO-40 as G4KLX. I hope to return to HEO satellites once one of the AMSAT birds is launched. My money is on P3E.

 

Last updated on 21.3.2004