FM Satellite Transponder Operating Etiquette (or 'Satiquette').

This page has received hits since November 27 1999

The South African satellite, SUNSAT, has recently commenced amateur transponder operation on the 2 metre and 70cm amateur bands. Unlike most amateur satellites, this 'bird' carries an FM voice repeater, which enables many more amateurs to experience the thrill of satellite operation. However, this accessibility, combined with the single channel available on current generation FM satellites means that congestion is a big problem which needs to be managed, if everyone is going to get their turn on the transponder. As SUNSAT has become popular here in VK during the spring of 1999, the problem of congestion and operating procedure worsened to the point that a lot of time is being wasted due to stations 'doubling' and having to re-transmit their signal reports or other information.

Satellite transponders, a quick overview.

This is a short overview on the different types of analogue satellites and how FM satellites compare to the linear transponders used on other satellites, as well as their terrestrial cousin, the FM voice repeater. Here is a table showing the differences and similarities between the different devices.

Characteristic FM satellite transponder FM terrestrial voice repeater Linear satellite transponder
Simultaneous users 1 1 Several
Crossband Yes No (usually) Yes
Availability Limited (active passes only) Continuous Limited (active passes only)
Coverage radius 3000+ km 20 - 200km (most cases) 3000+ km
Mode FM FM All (SSB or CW preferred)
Typical minimum uplink power. 1 - 5 watts EIRP Varies depending on location 10-50 watts EIRP

In the table above, several conclusions can be drawn. Firstly, like their terrestrial cousins, FM satellite transponders can support only one user at a time. This is one of the main constraints of these devices. Also, the uplink requirements are quite modest, well within the range of handheld equipment (successful satellite operation has been achieved with a few watts from within trains, trams and buses). Combined with the limited availability of the transponder and the enormous coverage possible, dogpiles and congestion are highly likely. It's worth noting that congestion isn't a serious problem on the linear transponder satellites due to the number of simultaneous QSOs supported, as well as the higher "barriers to entry" (namely multimode VHF/UHF radios and higher power and antenna requirements) To alleviate this problem, good operating procedures are a must.

Operating procedures for FM satellites.

Most material I've seen on satellite operation deals with linear transponders. While these procedures are mostly good operating habits and common sense, they do not specifically emphasise the key constraints placed upon the FM transponders, namely limited QSO throughput due to single channel operation, and higher levels of demand. As a result, any operating procedures must address these issues and ensure as many people as possible can make contacts during the pass. My suggestions are drawn from a combination of FM repeater procedures, contesting and traditional satellite operation, as elements of each of these facets are incorporated into FM satellite operation. I'll summarise my procedures below:

  1. First and foremost is to listen before and while (if possible) transmitting, to ensure your transmissions don't drown out a weaker station who may be on the edge of a pass or running QRP. Satellites should be an alligator free zone. It is strongly recommended that you set your station up so you can monitor the downlink while transmitting, so you can hear how well you are accessing the satellite and whether you accidentally clobbered someone else. Similarly, if you can't hear the transponder, don't transmit. Do something else more productive, such as realign your receiving antenna to improve reception.
  2. Be brief. Because the traffic levels can be quite high, contest style (callsign/signal report/next station) operation is the most appropriate for most situations. Many stations also exchange QTH and first names, which is OK if time permits. If transponder activity is low, you can have a brief chat, but the opportunities for this are becoming rare now.
  3. Take turns. If you've just worked a handful of stations, be polite and hand the transponder over to someone else so they can work a few. There may be an opportunity to call back in later during the pass and work some different stations as the satellite passes over different areas, and others will appreciate your courtesy.
  4. When calling, a simple announcement (e.g. "This is VK3JED listening SUNSAT" or even "VK3JED listening") will suffice, like it does on a terrestrial repeater. Anyone within transponder range will hear your call. A short CQ call ("CQ SUNSAT, this is VK3JED") is OK too. Long CQ calls waste transponder time and frustrate everyone listening. Save the long CQs for HF, where they're appropriate. Only call CQ when there's a distinct lack of activity, such as at the very start of a pass and sometimes late in the pass after everyone else has finished. A well placed CQ call late in a pass might alert someone ahead of the satellite that a pass has just commenced over their QTH.
  5. Wait your turn. If a QSO is in progress, wait until it finishes before putting in your call. Butting in too soon is rude and wastes precious transponder time as the stations involved in the QSO have to repeat themselves due to your QRM.
  6. Don't tune up! Believe it or not, there are stations who test their satellite access by dropping a carrier over the top of everyone and perhaps announcing "Hello hello". Simply putting out a call at the appropriate time will provide all the signal checks you need (and net you a worthwhile contact! :) ), without annoying everyone else on the transponder. If you're really that doubtful about your equipment, perhaps connect your dummy load, test in the shack and try again another day, rather than disrupting everyone else. If you just want to hear your voice, well a tape recorder or a pair of walkie talkies will do just as well...
  7. Reward good operation. If you're answering a call, why not reward the good operators and put the alligators last on your list of priorities. If all satellite users favour good operators, perhaps everyone will learn that good ops have the highest QSO rates and earn the most satellite awards. :-) Peer pressure is a powerful motivating force, as any teenager will know (but probably not admit to! :-) ).
  8. Use the minimum power necessary. While power levels are not critical on FM satellites (unlike linear transponders where an excessively strong signal can affect other QSOs on the transponder), using the minimum power necessary allows you to easier tell if you're 'doubling' with someone else. For the South African SUNSAT satellite, you shouldn't need more than 5 watts into a basic (1/2 wave handheld or turnstile) antenna, perhaps a bit more if the antenna is setup for terrestrial operation, to overcome radiation pattern limitations. As an example of good operation, recently one station who had multiple beams wound his power back to 20 mW. The signal into the bird was full quieting, but it was still possible to tell if someone else was underneath his signal. If he had run 100W, he couldn't have known if he'd stepped on anyone else, due to the capture effect of FM.

If everyone follows these simple guidelines (which are basically common sense and courtesy), then FM satellite operation can be enjoyable for everyone, regardless of whether you run a sophisticated satellite station or a couple of handhelds from the back yard. FM satellite transponders are like FM repeaters, only more extreme. On the positive side, they can enable minimally equipped stations thousands of kilometres apart to communicate with ease. On the other hand, the worst aspects of repeaters can be experienced as well, such as congestion, doubling and even the odd idiot dropping carriers! (I don't know how the idiots manage to always have a very strong signal, even when the repeater is 800 km off the ground!). The operators themselves (that's YOU!) have the power to determine what sort of experience FM satellite operation will be in the future.

A final note. I suggested that satellite operators listen to their downlink while transmitting for several reasons. Firstly, of course, to hear if you're accessing the satellite and that you're on frequency, and secondly to ensure you're not going over the top of someone else. Those who aspire to SSB satellite operation will need to be able to monitor signal so they can compensate for Doppler shift (which affects SSB much more severely than FM). To do this requires suitable equipment and a bit of skill. The equipment can be either a multi band transceiver with crossband duplex capabilities, such as some modern multiband rigs, or a pair of transceivers, one tuned to the uplink and one tuned to the downlink. You will also need headphones or an earpiece to avoid causing feedback when transmitting.

Hearing youself in your ears every time you transmit can be disconcerting at first, and being able to listen for heterodynes and general signal quality while talking can take a little practice. It's not difficult to learn, and practice is easy and shouldn't be intrusive on your normal operation. Some ways to practice self monitoring are:

Keep up the good habits and hope to hear you on the birds. 73 - VK3JED.

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