Going full-duplex with amateur satellites, part 1: introduction and I bought the hardware / 2017-03-26

I still want to get active on amateur satellites again, but the main reason is that the amount of work per contact is a lot more than for example in a digimode contest. But I still want to make those 'special' contacts, especially when the amount of local radio noise on HF is bothering me.

One of the most important improvements in making contacts on amateur satellites is working 'full duplex', meaning receiving signals while transmitting. The expensive way to reach that goal is buying a second amateur radio capable of receiving in FM and SSB modes in the 2 meter and 70 centimeter amateur bands and having computer aided tuning so gpredict can control the receiving frequency.

The less expensive way to reach that goal is using software defined radio. The good news is that Gqrx SDR can be controlled by other software which as the page shows is intended for remote control by Gpredict. All I needed now was reception hardware. Since the first RTL-SDR device I bought is always in use for receiving ADS-B signals from airplanes I decided to buy another cheap one to get me started. So it was on the shopping list for a recent visit to a hamfest.

At the hamfest I found a RTL-SDR stick with mcx connector and an mcx to bnc cable. But the same guy also sold cheap low(ish) noise amplifiers with SMA connectors and a 9V battery connector for power. So at one of the booths selling cable assemblies I found an mcx to male sma cable and a female sma to bnc cable, and a male to male sma cable.

The plan is to put this all together in some metal case to shield the lna from the outside world. Maybe also shield the amplifier from the RTL-SDR stick so it won't pick up any extra noise.

Should this work it would be possible to think of an upgrade with better SDR hardware and/or a pre-amplifier at the antenna side.

RTL-SDR stick and BNC cable

LNA and extra cables

Updates with progress:

• part 2 : Installing Gqrx SDR software and the first tests
• part 3 : metal cases
• part 4 : amplifier built into the case
• part 5 : first test of the amplifier with RTL-SDR
• part 6 : First succes in reception
• part 7 : Recording downlink audio
• part 8 : No real contact yet
• part 9 : Filtering the reception, in theory