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Sunday, 11 December 2016

Amateur satellite

After watching a segment of episode 12 of TX Factor about operating through satellites I thought I would give this a go myself as all I need to do this is a suitable dual-band HT, as all mine are Chinese one would think they wouldn't be suited, as they can do what the offerings from the big names can do then they are fine for the purpose.

The satellite I am interested in, and as noted on the TX Factor episode referred to above, is SO-50, as it has an FM transponder, with uplink on 2-metres and downlink on 70cm, as it would be massively impractical to use the -600kHz split on a satellite due to the size of the cavity filters used at 2-meter repeater sites that achieve this so the signal goes up on 2-metres and comes back down on 70cm, but it isn't that straightforward as the Doppler effect has to be compensated for, programming the HT with the frequencies for the satellite beforehand will save you trouble here, the frequencies for SO-50 and other Amateur satellites are available on the Internet.

Knowing when the satellite is to pass is another thing you need to know, I have already gone ahead and downloaded two pieces of software for this purpose, on my Android phone I have AmsatDroid Free, and for my laptop I have Orbitron, the latter software being mentioned in the same TX Factor episode noted above, and this runs fine on Windows 10, so now I know where SO-50 is at any given time the next bit requires I be able to transmit from my HT through the satellite and my HT's rubber duck antenna simply will not do, for this a Yagi is the best antenna to use, but it needs to be of a design that will work on both bands, the most popular antenna appears to be the "Arrow" antenna, the original of which is actually made from arrows for the antenna elements, and because we're doing cross-band operation we also need a diplexer (this is correct, it is not "duplexer"), which from what I can tell is simply two passband filters, one high-pass for 70cm and one low-pass for 2-metres.

The Arrow antennas are not cheap, so in the spirit of Amateur radio it makes perfect sense to build one using bits from the junk box, and from a DIY store (B & Q in my case as it is the closest one to the home QTH), and I like to build rather than buy antennas where I can to save money, and considering that one may simply use their arm to move the antenna with the satellite it needs to be lightweight, wood for the boom would work well here, but if you do use wood it should be varnished to protect it should you be out on that hilltop and the heavens open, waterproofing the coax connections is also advised.

Once you have all the information regarding your chosen satellite, an antenna, a programmed HT, go out and make some contacts, but be aware that satellite QSOs through SO-50 are similar to contesting, usually callsign, location (locator square) and signal reports as the satellite passes for a short duration and is often very busy, listening before keying up is well advised, as is the use of headphones so you can hear the satellite better, also run the radio with an open squelch.

As a foundation license holder I am restricted to 10 watts, as is anyone with a foundation licence, antenna gain may push your actual radiated power beyond this level so dropping the radio to a lower power setting may keep the foundation licencee within their power limits and still legally use the satellite, gain and other such factors are beyond the scope of this blog, and from what I understand SO-50 doesn't need more than 10 watts anyway into it and by the time the signal gets there it probably falls well below that.

Having a second person on hand to assist with the operation may also be a good thing, as they are not transmitting they do not need to be licensed, adding a second pair of headphones for the assistant to help with logging may be a good thing too, the assistant can also help position the antenna leaving you free to carry out the QSOs.

And finally, building the antenna simply requires a search on Google as there is a lot of information on the subject and many designs are available, and you could further this and build the diplexer as commercial ones are about £30+ depending on where you go, and you get the pleasure of building the entire thing yourself if you do, and save money.

I look forward to working some stations through a satellite very soon, just got to get the festive season out of the way first.

73 de M6RSQ

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