Automatic Antenna Switch (for working dual band satellites)

Let’s take a look at this electric diagram I made.

Starting from the end, is the coaxial relay, with two antennas in and the transceiver out.
The position of this relay, the selection of the antenna, is made by two means. The rotary switch sets the work mode, basically, which antenna you want for transmission and which for reception.
Then comes the cool part, that automatically switches to transmission antenna when you press the PTT, and to reception when paused.
This is the “Automatic” feature.
Obviously, the command is coming from the transceiver. All the modern transceivers have a connector on the back, called CAT/Linear, of which one of the pins is shorted to the ground when in transmission. So when Ground is detected on the electric diagram input, the relay is activated.

This coaxial relay has a set of contacts which I used as a feedback to see which antenna is selected.

This may seem over-complicated, but let me give you some examples of how this switch helps you, when working on satellites.

1. The Space Station’s voice repeater:
   – uplink frequency 145.990 MHz
   – downlink frequency 437.800 MHz
2. AO-91 (A.K.A. Fox-1B)
   – uplink frequency 435.250 MHz
   – downlink frequency 145.960 MHz
3. The Space Station SSTV and Packet frequency
   – uplink / downlink  145.825 MHz
4. I don’t know any satellite so far working only on UHF, but you might use this setting (as well as all the rest) for ground communication.

My setup for working on satellites consists of:
– Two antennas, one for VHF, one for UHF;
– Antenna rotator;
– Antenna switch;
– A computer with software to point the antenna and to adjust the frequencies;
– The CAT cable, and of course, the all modes, all bands, transceiver.

It’s complicated but necessary, because a satellite pass is so short, you have to do a lot of work in a very small amount of time, and this kind of automation lets you focus on actually making contacts.

I’ll post my successful contacts, if any, on my second YouTube channel.
https://www.youtube.com/channel/UCaJGOVHa-z-5BUj7swRmm-Q

FM Satellite Frequency Summary
https://www.amsat.org/fm-satellite-frequency-summary/

FM Satellites: Good Operating Practices for Beginning and Experienced Operators
https://www.amsat.org/wordpress/wp-content/uploads/2017/12/FM-Satellites-Best-Practices.pdf