[NLRS] Question about sequencing for an external RF amp

[Larry Peterson]

The main purpose of a sequencer is to protect an LNA (low noise amplifier...or you may think of it as a pre-amplifier).  Any Tx power and you fry it.

If you don’t have one and are just doing PTT-to-ground switching to turn on a linear, then it is really easy.  Just connect your PTT line between the rig & linear.  When you transmit, it turns on the linear.   

PTT switching is superior to RF switching, but I think we all do the latter...I have with Mirage & TE Systems amps.  But my Gemini’s and Beko’s call for the PTT-to-ground.

Now if you do have an LNA, like I have on my 10 GHz station, then a sequencer is a must.  FYI, here is my sequencing order:

1. Turn off voltage to the LNA.
2. Switch T/R relay to transmit.
3. Turn on DC power for my 8W linear amplifier.
4. Turn the DEMI transverter to transmit by activating the PTT-to-ground from my Yaesu 817.

Then when you are done transmitting, the sequencer goes back in reverse order to get back to receive mode.

It’s pretty fast but you can hear the clicking, etc of mechanical relays in sequence.

Good luck,

Larry 

> On Aug 9, 2019, at 12:53 PM, David Palm <thepalmhq at gmail.com> wrote:
> 
> I am just about done wiring the switching circuitry and RF relays to add an
> external 1296 MHz amplifier to my transverter (thanks, N4PZ!)  I know that
> there should be some sort of sequencing so that the relays don't hot
> switch, holding off Tx RF until they have had time to switch.
> 
> But while I've been pondering how to do that in this specific case (any
> suggestions are welcome), I thought about the TE Systems, Mirage, etc.
> amplifiers we regularly deploy on 144/222/432 MHz.  We don't have to do any
> additional sequencing for these amps, we just plug in PTT and RF from the
> transceiver and go.  Is this because the PTT signal out of our modern
> transceivers is already leading the RF output by xx milliseconds, so we
> have that time built in for the relays to switch?  If so, do I need to do
> anything else in this case, where I'm building my own relay transfer
> circuit?
> 
> Thanks and 73,
> 
> David  W9HQ
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