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|
|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:
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.
Satellites on Rails
The shack of VK3JED