Much like the beacon keyer presented here earlier, this RX/TX sequencer is a simple but useful little device. Its typical use is in ham radio applications when a separate power amplifier (PA) and/or a sensitive low-noise pre-amplifier (LNA) is used. Care has then to be take to safely transition between RX and TX states – and that’s where this sequencer comes in.
Why a sequencer?
There are many sequencer designs on the web, both analog (http://www.ifwtech.co.uk/g3sek/dx-book/sequencer/) and digital (http://www.mancuso.net.au/sequencer.html) There’s also a beautifully made but somewhat more involved design here: http://www.w6pql.com/relay_sequencer.htm. The links above (and many more) explain the purpose of (and need for) such a sequencer in quite some detail so I won’t repeat it all here.
soldernerd.com on YouTube
Maybe the best way to understand what this sequencer does is to see it in action. I’ve just yesterday started a YouTube channel to share that kind of videos. Here’s the link: https://www.youtube.com/watch?v=Ctxm0VxeM4g.
This is already Rev D
I have designed and built a number of sequencers over the years so this is already revision D. Unfortunately, I don’t seem to have photos of the first two versions.
Input and Output
The sequencer presented here is of the digital variety, uses a 12V power supply and is fully reverse-polarity protected. It is controlled via a PPT input which is pulled high (to +5V) with a 10k resistor and active when pulled to ground.
for more detail: RX/TX SEQUENCER