Satellite Operation - How to know you made the contact

Modified on Thu, 03 Aug 2023 at 02:07 PM

An important thing to remember when trying to work an Amateur satellite is that you need to be able to monitor the satellite's downlink frequency SIMULTANEOUSLY as you transmit on its uplink frequency. This will generally mean that you are going to need two radios, as the vast, vast majority of Amateur radios do not have a feature called "Full Duplex." 

Full Duplex is the ability to transmit and receive at the same time. Think about a normal phone call- you can talk and also hear the other person talking at the same time. Most Amateur radios don't work that way. You push to talk and release to listen- you can't do both at the same time. 

For Amateur satellite work you need to be able to transmit up to the satellite and also hear the satellite "talking" back down to you. That is to say, you need to be able to "hear it hearing you" in real time. An Amateur satellite is essentially a spaceborne repeater so what you'll be hearing on its downlink is your own transmission. Same result as you'd expect if you were to transmit on a typical repeater's input frequency with one radio while listening to the repeater's output frequency using a different radio at the same time. 

Monitoring the satellite's downlink makes it possible to quickly and accurately adjust for the doppler effect while the bird screams along at 25,000 mph on its track in low earth orbit. It's also important so that you know if you're making it in to the satellite to begin with. You can be doing everything properly- aiming at the correct piece of sky on the correct frequency at the correct time of day, all while holding your mouth just right- and still fall prey to the dreaded capture effect and never make it in to the satellite's receiver. If you can't hear the satellite's downlink then you'd never know your signal got overpowered and would just be frustrated in the dark. 

Back on the topic of full duplex- even if your high end, super slick new HT has two separate VFOs and can hear two different frequencies at the same time, it probably can't full duplex. It's just an extremely uncommon trait for Amateur radio handhelds to have. It's Important to note that full duplex IS NOT something that can be programmed with software. Either the radio can do it out of the box, or it can't.  

The last HT from a major manufacturer that this author is familiar with which had full duplex capability was the venerable TH-D72 tri-bander from Kenwood- it remains extremely popular with Amateur satellite enthusiasts even though Kenwood isn't making it anymore. The newer D74, while a marvelous machine, does not have full duplex capability nor do any current production handhelds that I know of from Icom or Yaesu. 

The Icom 9700 base station radio is designed with Amateur satellite enthusiasts fully in mind and has a whole suite of features specifically tailored for working the birds. Fire up the RT Systems 9700 programmer  and you'll find a tab at the bottom of the window specifically for satellite memories! Notice that those memories are broken down in to pairs of TX/RX frequencies- (1TX/1RX), (2TX/2RX), etc. Those are for the satellite's uplink and downlink frequencies.

For a more robust explanation of all things Amateur satellite related I would highly encourage you to check out the wonderful resources provided by the outstanding AMSAT organization on their website at

Find the product page for the RT Systems 9700 Programming package here - WCS-9700 Programmer

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