This page describes my homemade sequencer. It controls the components of my EME station.


Sequencer controls station
Fig. 1. The sequencer (yellow) controls my EME station.

The sequencer is highlighted in figure 1. Three events must take place in a specific order when PTT is activated and the system switches from RX to TX.

  1. Disable the preamp (remove 12V from port 1)
  2. Change relay1 and relay2 from RX to TX (port 2)
  3. Enable the SSPA (port 3)

When PTT is deactivated, the system switches from TX to RX. The events are now executed in reverse order.

  1. Disable the SSPA (port 3)
  2. Change relay1 and relay2 from TX to RX (port 2)
  3. Enable the preamp (apply 12V to port 1)

Circuit Diagram

circuit diagram
Fig. 2. Circuit Diagram.

The preamp is in RX mode when 12V DC is applied. When 12 V is removed during TX, a relay in the preamp will ground the input and protect the electronic circuit.

The heart of the sequencer is the Relay Sequencer, which is a kit developed and sold by W6PQL. I have modified the circuit to get 100 ms between each event. I've added overvoltage protection on all control ports. It was necessary to move the LED D10 (on the W6PQL PCB) to a small Veroboard because D10 was on during RX. This was caused by the low voltage (0.7 V) at the base of T1. 

separate PCB
This circuit controls D10.

The "W6PQL Relay Sequencer" has an unused 4th output (Event4). This output can be used for enabling a transceiver.
Fig. 3. Front view. Click to enlarge.

rear view
Fig. 4. Rear view. Click to enlarge.

view inside the sequencer
Fig. 5. Inside the sequencer. Click to enlarge.

Another view inside the sequencer
Fig. 6. Another view inside the sequencer. Click to enlarge.

Written by OZ1BXM Lars Petersen. Latest revision: 15-June-2017