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External sequencer with the IC-910H



Hello the NET:

A sequencer is needed to properly transition the PA, IPA, transverter, 
transceiver, and preamplifier
when going from RX to TX and TX to RX.

The objective is to add a very short  time delay to avoid sending QRO RF 
power into the preamplifier
or into an open, just closing relay contact, like "hot switching" which 
significantly reduces contact life.

I use my IC-706MK2 transceiver with a Lunar Link QRO amp for terrestrial 
modes.

These techniques are applicable to any transceiver, PA, IPA preamp 
configuration.
Just different microphone connectors are used.
I apply the same techniques to the FT-847 and the FT-1000MP (IF rig).

DEMI offers a sequencer kit at about 35$US, Advanced Receiver Research, 
SSB,
JWM engineering, LNA technologies, W1GHZ, and others also offer non kit 
versions.
The DEMI design uses relays with a 2 amp contact rating, others can be 
much less.
All have their unique variations.

I grab the microphone PTT line, before it gets to the radio, route it to 
the sequencer input,
then take the sequenced outputs:
DC power to the preamp and bypass RF relays, 2 each SPDT legal limit 
rated RF relays
PTT, ground to TX,  to the QRO PA,
PTT, ground to TX,  to the IPA (or transverter)
PTT ground to TX, to the transceiver

For RX to TX,
preamp and transfer relay power is dropped, bypassing the preamplifier
time delay ~ 250 milliseconds in the unmodified DEMI sequencer
PA  TX is enabled
time delay, ~ 250 milliseconds
IPA/transverter TX is enabled
time delay, ~ 250 milliseconds
transceiver TX is enabled for SSb , CW, FM, whatever modulation

This timing constant, in the DEMI sequencer, is a RC network and can be 
modified for a faster
time delay.

For TX to RX, The sequence is reversed.
Some sequencers simultaneously change all output states, without a 
sequenced delay.

Most sequencers allow enough flexibility to configure PTT ground to TX, 
or PTT +V to TX
Mostly with "dry"relay contact closures for a real 0.00V on grounding, 
unlike a solid state switch.

I put the sequencer in a diecast box with a 4 pole multi position 
mechanical switch to route the sequencer outputs.
pole #1 is for local indicator LEDS to show what band I am controlling.
pole #2 for the preamp/bypass relay power
pole #3 for the PA PTT control
pole #4 for the IPA/transverter PTT control

The transceiver PTT is always the same, and not switched. Your 
configuration may vary.

Avoid any break in CW keying. always force TX mode (with a manual PTT 
switch), before using CW

One switch position per band.

Stan, W1LE  FN41sr   Cape Cod




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