It’s very important that your transceiver – PA – preamp and maybe more, are getting the signal at the right time, else can something be damaged. For example when the PA is sending and the relay in the tower with preamp, still is in receiving mode – your preamp will be destroyed. So to get it switched at the right time before sending and also the other way – switch back after signal from PA is stopped – you have to tell what has to switch first or last.

                         This is version 2 of my sequencer with minor prog. changes and a TX inhibit input.


In this sequence from PTT, it’s all starts when PTT goes low. First relay to switch when sending, is the preamp relay by the antennas. Next come PA – later the transverter and last not least wil the transmitter be keyed to start sending each with a delay between. After transmitting is finished, the PTT comes up again and all will be switch backward in the right order so that not any of the units are damaged.
The delay between the switching of the sequence, can be changed with jumpers on the board.

Here you can see the PCB that I have made. All is controlled by a ATmega328P microcontroller that got a program from Arduino. It has 4 outputs at the bottom, that are switched in sequence, but when only 3 are needed, just leave the last. Note that each output can be grounded with a jumper near the relay.
To the left are 3 input terminals. At the top is power plus 12V and minus. The circuit can function on 5V when the 5V regulated is bypassed. In the middle is PTT input and at the bottom left you have relay return input. My relais input needed a 1K resistor in parallel to ground to work correct.
The top left are jumpers. First 4 from left are: Delay D-A.
A: 30 mSek, B: 40 mSek, C: 50 mSek, D: 75 mSek
The 5 jumper is for enable reverse status input from relay and number 6 is enabling status from relay.
Last connector in lower right corner is for TX inhibit that I now have added. Programming socket is the smal 6 pin header near the microcontroller.
On the picture, are all light diodes mounted on the PCB top. But instead on the PCB I would add some wires instead to the front of that box you can place it in. It’s good to see action status on the front of your case where it is mounted 🙂
Hope it gives sense how it works – else contact me.

P.S. – The four transistors in the schematic is of the MMBF170 N-Channel FET type or equlent type BS170 and component placing picture can be found down under.

Note that the 4 FET transistors and the 4 diodes near relays – are SMD types, and are placed on the solderside.