Masthead + PA + Radio Sequencer


My 2m station includes a masthead preamp, a 2 x 4cx250 linear and the IC-910. In order not to blow up the preamp I needed to get a sequencer, me being me I decided to design and build one, total cost with the box was around £10. This is a very simple design and uses a PICAXE-08M for the control as it supports 5 input/outputs. All I needed was 1 input (PTT) and 3 outputs, preamp, TX Amp and radio. The preamp, TX Amp and radio outputs are driven by relays so can be configured for NO or NC when the sequencer is not active, the non sequenced state can also be set in the software too.

The delay on TX is 100ms between the preamp going off and the TX amp coming on and then a further 50ms for the radio to move into TX. On un-keying the radio is moved into RX, 50ms later the TX amp is removed then 100ms later the preamp comes back on. My initial design used 4 LEDs, a green one for power, one red/green for TX/RX, a green one to indicate preamp on/off and a red one for indicating the TX has come on.  You may decide to omit some of them.

IMG_20100706_223818 5260843_orig IMG_20100706_223740 IMG_20100706_223757

Updated to v1.2

I’ve done some updates to the design based on feedback from users.  The main update was to add a means of adjusting the timing sequence manually so I added a potentiometer to one of the inputs and read the ADC voltage on it.  The ADC value is then added to the default value giving an additional delay meaning the sequence delay can be set between 100ms to about 1 second.

The update also allowed me to clean up the code by adding comments and symbols.  this should allow whoever builds it better understand how to customise the outputs and give a better overall understanding of the PICAXE code if they are new to it.

NOTE: If this design is to be used with a radio which goes into transmit when the PTT line is grounded then you can omit D3 and REL3 and connect the PTT line of the radio directly to the collector of Q3.


Download v1.3 of the code directly.

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