How to Work 3B9C : Satellite

How do I work 3B9C on Satellite?
by David, G0MRF

3B9C hopes be operational on Amsat Oscar 40 (AO-40).

February 2004 Update:
Operations will be subject to AO-40 being available. We continue with details here, on the basis that during the 3B9C operation, AO-40 operation may be possible.

AO-40 Operation
This satellite can receive your signals on UHF and retransmit them on 2401 MHz. To work us on AO-40 you have a couple of choices. If you would like to invest in some satellite equipment then the following brief guide describes the equipment you’ll need to find. If however, you just want to sample satellite communication and make a QSO with 3B9C in the process, then you could contact your national Amsat organisation. If you’re lucky there will be an Amsat member close to you who give you some help, or perhaps, let you visit and make a QSO on AO-40. Both Amsat-NA and Amsat-UK have ‘elmers’ who can answer questions about satellite operation.

Transmitter: To work AO-40 you will need a CW / SSB transmitter, either on 435MHz or 1269MHz. The total ERP required on 70cms for a reasonable SSB signal is about 800 Watts. With CW, 200 Watts ERP will make the distance. While this may seem a lot of power, antennas on 70cms are quite small. You can generate 200W ERP with just 20 Watts of RF and a 10dB gain Yagi. On 70cms a 10dB gain antenna is only three feet long. Remember this is for a reasonable signal, if you pick a time when there’s not much activity then you can run even less power. On occasions, 5 Watts and a small beam will get you a 559 report.

Receiver:  AO-40 transmits signals on 2401 MHz. To receive this microwave signal you’ll need a ‘downconverter.’  This is a small unit that converts the 2401MHz signal down to another frequency, usually 145MHz. Back in the shack you simply tune across the 2m band and listen to all the activity on the satellite.
To avoid losing signals from attenuation in the coax, the  downconverter is mounted at the antenna. For 2401 MHz a small dish is the best choice. Downconverters start at around 80 US dollars and are available from several suppliers, complete or in kit form.

Tracking:  Before you can have a QSO with  3B9C you will need to work out where to point your antennas. AO-40 is available for up to 14 hours a day and the easiest way to locate the satellite is to use a tracking programme. On Rodrigues we’ll be using Nova for Windows, but there are several freeware programmes that can do the tracking job just as well. If you want to monitor the DX on AO-40 online then you can view what’s happening in real time on the AO-40 activity logger.

Operating:  With your satellite station complete and pointing in the right direction, you are ready to go. First, you must find a time when the satellite is above your horizon and the transponder is on. This is best accomplished by looking at the tracking programme and the satellite schedule. Then, move your antennas until you find  the satellite’s middle beacon. This transmits a constant stream of PSK telemetry on 2401.323 MHz.  The beacon is quite distinctive and most QSOs will take place within –50 to +100 kHz of that frequency.

Next, you need to transmit up to the satellite and listen for your own signal on the downlink AO-40 is full duplex so you can transmit and receive at the same time. Remember that the satellite’s range can be up to 63,000km. At that distance you will hear a time delay of up to 400 milli seconds between transmitting a signal up to the satellite and when you hear it come back down. This isn’t due to any electronics in AO-40. What you’re hearing is the delay due to the finite speed of light!  When finding your signal, be sure to transmit in a quiet part of the passband. Under no circumstances ‘swish’ the transmit signal up and down or transmit on the beacon frequency. A good technique is to transmit a series of CW ‘dits’on 435.700 and to listen for your signal about 35kHz below the beacon. A comprehensive list of frequently asked questions on AO-40 is recommended reading. An uplink and downlink frequency chart is also available.

3B9C will be using CW, SSB and running Ham Radio Deluxe for PSK31.

Read more about Oscar AO-40.