[NLRS] More on sequencers (L O N G)

[John P. Toscano]

Chris Elmquist wrote:

> OK.  This is even better.  This is very close to my dream radio which has
> a "Clear To Send" input.  With this sort of capability, you can hold off
> the RF as long as you like while any and everything external gets to the
> right place.  Nice.  Do you still get a PTT output from the radio that
> goes active when any transmit function is activated?  This I would call
> "Request To Send"...
> 
> So, you cause the IF radio to transmit--  it asserts "Request to Send".
> Your sequencer now starts and begins flipping relays and keying
> transverters, amps, etc.  The last step the sequencer does is assert
> "Clear to Send" back to the IF rig which allows it to finally make RF.
> 
> And this works no matter what mode the radio is in right?  CW, VOX, FM,
> whatever.

Chris, the idea of a "Request to Send" and a "Clear to Send" is 
basically what Jerry was proposing by saying you need a little box 
external to the IF radio, into which you attach the mike (and, though he 
didn't mention it, a footswitch is a great idea also).  The PTT button 
on the microphone (or the footswitch) becomes the "Request to Send".  It 
goes to the sequencer, and the LAST stage of output from the sequencer 
is the "Clear to Send" that connects back to the radio's external PTT input.

For a 4-stage sequencer, the events could be set up as follows:

RTS from microphone or footswitch to sequencer INPUT.

SEQ OUT 1:
   o If using a voltage doubler block to create 26-28 volts (for relay
     switching) from 13.8 volts, enable it.  In some cases, you may not
     want to switch this function, but generate the 26-28 volts "all the
     time" (as long as the whole system is powered up).
   o Energize the antenna T/R relay so that the antenna is disconnected
     from the preamp input (or transverter input if no external preamp),
     and is connected to the PA output (or transverter output if no
     external PA is used).
   o Energize the T/R relay at the antenna connector of the IF radio, so
     the IF radio is connected to the transverter IF input and is
     disconnected from the transverter IF output.

SEQ OUT 2:
   o Key the external PA, if present.  Many have either a "ground to
     enable" input, a "pull high to enable" input, or else an
     interruptible bias line that disables the PA when the bias is
     removed, and enables the PA when the bias is present.  The 902 MHz
     amplifiers that many of us have seen at a NLRS breakfast, or on
     eBay, work this way.
   o If using an external preamp, and it has an input that disables it,
     then use this sequencer stage to disable it.  You want to understand
     your preamp well, however, because some of them are MORE susceptible
     to damage if stray RF comes in when they have no power applied to
     them, so if you are doing this, make sure it is a HELPFUL thing and
     not a HARMFUL thing to do.

SEQ OUT 3:
   o Key the transverter's PTT line.

SEQ OUT 4:
   o Key the IF radio transmitter's "Clear to Send" input


I guess that the "next best thing" would be to NOT do anything fancy 
with the IF radio's PTT (i.e., split RTS and CTS), but simply use the IF 
radio PTT to drive the input to the sequencer.  With this setup, you 
probably want to switch the IF radio T/R relay right away (i.e., not 
delay it through stage 1 of the sequencer), so that the IF radio 
transmits into the IF INPUT instead of the IF OUTPUT of the transverter. 
  There would be no harm in also immediately switching the antenna T/R 
relay at this time, since the transverter won't be transmitting yet, so 
that relay won't be "hot switching" even though the IF radio will be in 
transmit mode.  For that matter, it's probably OK to key the PA at this 
time, since it will have no RF coming in from the transverter, so the 
main antenna T/R relay will still not be hot-switching.  But as long as 
you have a 4-stage sequencer, you might as well do the T/R's before the 
PA.  Then, the final step is to key the transverter.  At that point, the 
transverter starts to emit RF, but all the relays are in the correct 
position and the PA is ready to go.  In this simplified mode, you can 
get by with only ONE delay stage (the PTT in to the transverter), but 
TWO of them would be better (what I have shown as SEQ OUT 2 and SEQ OUT 
3 above).

Even though this setup is not optimal, I guess you have to ask yourself 
"is it good enough?", or alternatively, "is it any better than no 
sequencing at all?".

I suspect that most of us aren't using any sequencing on most of our 
systems, and in general, we haven't had a lot of them blow up.  (This 
suggests that it doesn't have to be "perfect" to be "acceptable".)  But 
in cases that *I* am aware of, when something blows without a sequencer, 
it's a preamp or transverter receive section or a damaged T/R relay, not 
the IF side of the transverter.  (This suggests that the IF side of the 
transverter is reasonably robust, and the fragile part is the most 
sensitive receive circuits of the transverter RF input or preamp, and 
the main T/R relay if hot-switched with a high-power PA.)  So, from 
these data, I conclude that "the next best thing" is worth a try.

Further evidence of this line of thought comes from the design of the 
W1GHZ sequencer.  It makes no provision for RTS/CTS control over the IF 
rig.  It is designed to take the PTT output of the IF radio to do the 
rest of the sequential activation, and as a "fail-safe", ALSO does RF 
sensing of the IF output to activate the sequencer if, for some reason, 
the PTT signal from the IF radio fails to reach the sequencer.  (I'd 
suggest you read his PDF file of his sequencer even if you don't plan to 
use his model, it has a nice discussion in there.)

Personally, I wish that transceivers had a simple PTT IN and PTT OUT 
jack, even if by default one was simply jumpered to the other.  Like a 
high-end audio amplifier system where the preamp output jack is jumpered 
to the power amp input jack by default, but you can pull off the jumpers 
to insert a component between them, such as a graphic equalizer.  But, 
by gosh, in a mass market, the cost of two more jacks on the back of a 
radio could bankrupt the manufacturer or drive the price up so high that 
no ham would buy it!  (Hopefully, y'all recognize sarcasm there!)

The FT-817 inhibit Tx input that Glen mentioned sounds like just what 
the doctor ordered, although it is not quite RTS/CTS.  (It is "Request 
to Send" / "NOT Clear to Send".)  You just have to set up SEQ OUT 4 so 
that it defaults to drive the inhibit Tx UNTIL the 4th stage of the 
sequencer is activated, at which time the inhibit Tx signal is REMOVED. 
  That causes the IF radio to transmit last, which is just what you 
want.  On the DEMI sequencer, each sequencer output has both a NO 
(Normally Open) and an NC (Normally Closed) section, so this is easily 
accomplished.

Anyway, thanks for bringing it up, Jon.  I've been planning to use the 
DEMI sequencers on my 2304 and 3456 systems when I add the PyroJoseph 
amplifiers, and this discussion got me to think about it all a bit more 
explicitly.

73 de W0JT