OBSERVATIONS GM1SXX 15th NOV 2009
Welcome to the ZOO
As some readers may know, I'm one of two administrators for the Yahoo EU-AMSAT group. There used to be three of us, but unfortunately we are now only two, after the death of Makis (Mak) SV1BSX. I'm bringing up the subject of Mak because Makis coined the term 'ZOO' to describe the bedlam that ensues when FM satellites come into range of Europe. For some reason, European radio amateurs have absolutely no patience to wait in line for access to FM satellite transponders. This fact surprises some people, but certainly not myself and John LA2QAA, because we have both complained about the unsuitability of FM as a satellite operating mode for longer than either of us can reliably remember!
If you have no idea of what I'm talking about, perhaps coming to these pages as a newcomer to amateur satellites, have a listen to any of the files in the clickable link. We hope to add to them as time permits.
The 'ZOO' only happens on satellites carrrying FM transponders, and IMO, it can in large part be explained by looking at contention ratio. In networking system, and that includes satellite networks, the contention ratio is "the ratio of the potential maximum demand to the bandwidth available".
With FM birds, the 'system' can only carry a single QSO in a particular time slot, whereas with Linear transponders, as many users as can fit into the available bandwidth can be accomodated. Since CW signals are normally very narrowband and SSB signals are typically only 2700Hz wide, many users can be accomodated in a typical 50KHz wide linear transponder.
It's certainly true that operating procedure and general 'manners' in Europe are poorer than in some other sreas of the World, and that congestion alone is not responsible for the ZOO experienced here on FM satellites, but it *has* to play a part. For anyone (Globally) who has used a linear transponder birds and conducted real QSO's rather than just cryptic 'rubber stamp' exchanges, FM is a massive disappointment. Of course, in heavily populated areas of the World, the contention for transponder access adds to the problems. It has been pointed out to me that in the US and Japan, they don't generally suffer from the 'ZOO' issue in the way we do here. certainly in part, that's to do with operating procedure being better there, especially in Japan where there are *many* radio amateurs competing for access.
Perhaps we have become 'spoiled' by linear satellite systems, but the fact remains that FM is easily the least suitable communications mode one could choose for a satellite network in terms of bandwidth efficiency.
I imagine that the AMSAT 'brass' at the time were probably thinking 'how can we encourage more people to join the organisation' when they thought up the idea to use FM. After all, FM transceivers are widespread and plentiful in most places in the World. Building and flying FM transponders included those who would have otherwise been excluded by virtue of the equipment they owned. This of course in itself doesn't make FM a good candidate to use on a satellite, being driven by politics rather than practicality.
Many people in the UK are strongly against FM birds. I was a member of AMSAT-UK for many years, but when I discovered that the board had decided to divert funds to the AO-51 project, I left the organisation and joined AMSAT India instead because at the time, they were working on VUSAT , HAMSAT or plain old HM-1, as it was actually known. (No wonder people get confused!)... then it was renamed yet again! to VO-52!
HM-1 was a linear transponder satellite.
I was told afterwards that AMSAT UK lost close on a third of their membership at that time (the AO51 project). Obviously FM was proving to be unpopular here :-) I still 'vote with my feet' only supporting projects I think are worthwhile. Why would anyone squander valuable money? Worthwhile for me means having a linear transponder on board.
Why am I so against FM? Well, actually I'm not! I really like FM. It offers good voice quality on phone and is very suitable for local rag-chews. I just don't see the point of putting FM transponders in space. The best analogue I can think of is 'You wouldn't enter a donkey in the Grand National, would you?'.
73 Al.
GM1SXX
(gm1sxx at amsat.org)