AmateurRadio.com

The International Space Station has had its packet BBS / digipeater active for the last few days on 145.825MHz. Noel G4PEW asked me in a short APRS chat last night if I had tried listening to it. It had been a long time since I tried bouncing anything off the ISS as I got fed up with checking if the station was operational and finding that it wasn’t, so I decided to give it a go to break the monotony of nothing much happening terrestrially.

There was a good pass this afternoon and I received ten stations. I even received my own digipeated beacon and a copy of my reply to GM0ICF’s message to ALL. Unfortunately my own transmissions didn’t show up on the map and list of stations that worked through the ISS at ariss.net as it appears that I was the only station gating the signals from the space station to the internet, as the list above shows (you’ll need to click on it to enlarge it enough to be readable.)

I was using APRSIS32 to send the beacons and messages and I guess that it didn’t gate my digipeated packets as having been received via the ISS because it had already sent them to the internet direct at the time I sent them.

I’m surprised that none of the other stations sending signals up to the space station were gating them during the receive periods. We aren’t talking about important communications here, just seeing if it can be done, but it would be nice to have the proof of it afterwards. Come on, chaps, play the game and get your gateways working!

There was recently a change of crew at the International Space Station and one result of that has been the reappearance after a long absence of the packet radio digipeater on 145.825MHz. When the Space Station passes over you can receive some very strong signals from it. I have decoded APRS beacons on a VX-8 handheld standing on a window sill inside the shack. But it is even better to use the main station, then you can see the positions of the stations you received on a map.

When using the ISS you need to use different settings to what you would use for terrestrial APRS. Digipeating, if enabled, must be turned off. You want to be connected to APRS-IS so you can gate received packets to the internet, but you don’t want to send anything received from the internet out to the ISS. You probably don’t want to display data from the internet on the map, to leave it clear to show those stations received by the radio. If you want to transmit through the ISS yourself you must also change the APRS path to “ARISS”.

After thinking that we really need an ISS option in APRSISCE/32 for this it occurred to me that all I needed to do was make a copy of the program in a new folder, then I could change the settings however I wanted without affecting the copy I use for terrestrial APRS. It worked fine. It was fun to see the stations heard via the satellite show up on the map, although when the map is zoomed out to cover such a large area the icons are hard to see. It was also amusing to see that the icon for the ISS’s own beacon was a bicycle. Perhaps someone should tell NASA!

After several abortive attempts to get my own beacon digipeated by the Space Station I set the transceiver to Narrow FM and got through on the first attempt using just 10W to my 300ohm ribbon cable Slim Jim in the attic. The proof is in the map of stations heard through the ISS at ariss.net.

Not a very useful activity perhaps, but fun to try.

Computers and radio really don’t mix. I was trying to connect the FT-817 to the shack computer. I plugged the USB cables into the back of the PC, then as I lifted the cables vertical to feed them behind the shelf unit I heard the noise level on 2 metres come up quite clearly. I could probably reduce the noise using clip-on ferrites but any more noise than I already have is unwelcome. I think I might give up the computer altogether and go back to paper logging!

I also proved today that it isn’t possible to work satellites with indoor antennas. Yesterday I tried receiving AO-51 with the 3/4 wave vertical I made, but I got a readable signal for only a few seconds. Today I tried the 6 element Yagi I made a few weeks ago which received signals off the Moon when used outdoors. Pointing it at the satellite from inside the shack I again heard only a few seconds of signal from the satellite. I think there is just too much attenuation at 70cm to use indoor antennas, so satellite operation is out of the question.

I could probably combine the 6-element 70cm and the Moxon 2m antenna to make a portable hand held antenna for satellite use. But whilst it would be an interesting challenge to make a satellite contact using the FT-817 and a hand held antenna out of doors I had really hoped to be able to do it from inside the shack.

I have been listening when time permits to see whether I can hear – and perhaps even work through – amateur satellites with my attic antennas. Today I caught a couple of passes of Amsat Oscar 7 operating in Mode B.

Oscar 7 is the first and only satellite I have ever worked through. It was launched in 1974 and I used it during the summer of 1975 when I was home from university. In those days I used Oscar 7’s Mode A (2m up, 10m down) running 50W from an Icom IC201 with an amplifier to a 5 element Jaybeam and receiving using some kind of wire antenna and a Yaesu FRG-7 receiver.

Oscar 7 is more than 35 years old and the fact that it can be used in 2010 is interesting. The satellite failed in 1981 after all the batteries failed short-circuit and that was the last anyone expected to hear of it. But in 2002 its beacon signal was heard once again after one of the batteries went open-circuit allowing the full power from the satellite’s solar panels to be used to run the transponders. Jan King, W3GEY, who built Oscar 7 in his garage all those years ago, wrote about his feelings on hearing his ‘baby’ again – it was clearly an emotional experience.

The satellite now comes on when it is in sunlight and goes off when it is in eclipse. It is pot luck which of its modes it uses when it comes on, but it mostly appears to be Mode B, the downlink of which can be heard on 145.950MHz USB plus or minus 20kHz. You can receive it quite well using a good 2m vertical – in fact I hear it better on my Slim Jim than I do on the SuperMoxon due to the fact that the latter is very narrow band and tuned to the low end of the 2m band.

You would hear the Mode A downlink on 29.450MHz plus or minus 50KHz. (Both transponders are linear and can support multiple contacts at the same time within the bandwidth, unlike an FM repeater.)

I am finding it difficult to find out which of the many amateur satellites now in orbit are usable for communication and when they are actually available. Many of the websites giving information about how to use satellites are well out of date and give details of satellites that are no longer operational. To add to the confusion some sites use names like “Hamsat” or “Echo” while others use the Oscar designation. So you may find the links below useful if you would like to try listening for Oscar 7.

N2YO has an excellent site for all satellite enthusiasts which provides real time Oscar 7 satellite tracking and allows you to generate predictions for future passes. It’s worth logging in to the site so it can remember your location co-ordinates. You should also tick the box “Check to show ALL passes (visible and not visible)” – confusingly this refers to when the satellite is visible to the naked eye, not when it is above the radio horizon.

The Oscar Satellite Status Page lets people enter reports of satellites heard so you can see which ones are operational and get an idea of which mode Oscar 7 is operating in at the moment. Finally Planet Emily has a lot of information about Oscar 7 including a log where people can record contacts made through this antique piece of space hardware.

I attempted this morning to make a 5/8 wave ground plane antenna for 70cm out of some solid copper mains cable and a chassis mount SO-239 connector. I tried two designs for the radiating element with a coil at the bottom, but both gave “High SWR” from the FT-817 and were so far away from a match that there seemed no hope of getting anywhere. My SWR analyzer doesn’t go above 200MHz so that wasn’t any help in finding out what was wrong.

After these abortive attempts I decided to straighten out the coil and make a 3/4 wave ground plane instead. This gave a perfect match with barely perceptible reflected power being shown on the SWR meter.

The four radials are each 165mm (6.5in.) long and the vertical element 483mm (19in.) The radials need to be horizontal for the best match, not slanting down as they usually are for a quarter wave vertical.

Hopefully I will be able to receive satellite downlinks with this. There are no 70cm repeaters in this area and no 70cm activity that I know of so it will not be much use for anything else.