D-STAR vía Satélite

An AO-27 question-and-answer page is available on the AMSAT-NA web site, with updates by Ray, W2RS. The URL is:
http://www.amsat.org/amsat/intro/ao27faq.html.

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On July 1st, 2007 during the 20:00 UTC pass over North America, AO-27 was again providing a new round of enjoyment for Amateur satellite experimenters. Thirteen years ago, AO-27, which coined the term "Easy Sat" by employing an FM bent pipe in space, provided many hams the ability to use a satellite without the expense of multi mode radios.

This time around, AO-27 was used to provide the first D-Star via Satellite contact between Michael, N3UC, FM-18 in Haymarket VA and Robin, AA4RC, EM-73 in Atlanta GA. Signals were reported as strong and easy to copy. Call signs were received digitally on both sides of the link. Communications were possible for most of the pass. Both Robin and Michael were surprised at just how well the digital link was received.

The Analogue repeater on-board AO-27 is well suited for D-Star work. The radios were designed to pass 1200-19200 baud GMSK data. The Analogue mode was not a primary mode of operation in the design. Using a free switch setting in the switching board, the design team hooked up the output of the receiver to the input the transmitter to create the Analogue mode. There is not the normal low frequency filtering that is found in normal FM Repeaters. This means the Analogue mode passes the low frequencies required by D-Star.

The equipment for the contact were IC-2200s on the Uplink at both N3UC and AA4RC, an IC-2820 on the downlink at N3UC, and an IC-91AD on the downlink at AA4RC. Doppler shift did prove to be a minor problem while using these radios. The D-Star signal would decode out to about 1.5 KHz in frequency error. The IC-2820 would only tune on 5 KHz spacing (the 6.25 KHz channels did not fall in the right locations to help.) so at times we could not decode the digital signals.

For others that want to try D-Star via Satellite we have a few things to keep in mind.

1) Remember that the FM users can't hear you on the bird.
They hear a strong "noise" but can't decode you. So please keep the D-Star transmitting short.
If you can monitor the FM side, you can time your transmitting as to not step on them.
Please try to schedule with other D-Star users instead of calling CQ for the entire pass.

2) Watch the doppler, at times you may not be able to decode a signal even if the other station can decode you.
Keep your uplink on 145.850 for the entire pass. Program your radio call signs the same as for simplex, AO-27 does not have a D-Star call sign. You don't need to set up your radio for repeater use.

3) Before using other satellites besides AO-27, please check with the control operators of those satellites. Every
FM satellite may not pass the D-Star signal nor may the control operators wish to have D-Star traffic on the bird.

4) If you here us on the Bird, please give us a call. We would love to have as many D-Star users on AO-27 as possible.

The AO-27 Control Operators fully support and encourage the use of D-Star via Satellite on AO-27.