[NLRS] Sequencer part II

[W0ZQ@aol.com]

Thanks to all who provided recommendations for a sequencer.   I've been 
"good" this year so Santa is bringing me a 6 watt amp for 10 GHz.   My current 
system runs 1 watt and does not use sequencing.   When I put my 1 watt system 
together I was a bit nervous about the lack of sequencing, but its been OK so far 
and I haven't blown any receiver inputs.   In talking with KM0T he mentioned 
that he also did not have any problems at the 1 watt level or so but that when 
he added more power he did blow the front end ; hence he now uses the DB6NT 
sequencer.

Thanks everyone for sending me their thought and recommendations for 
sequencers.   One thing that is obvious is that you really need to tailor design your 
sequencer for your system for what you need it to do .... there are some very 
good general designs that I'm sure work just fine.   For my 10 GHz portable 
system I want to control the attack and decay times for both the antenna relay 
and the Vcc for the 6 watt amp based on the IF rigs PTT control line.

I chose to use the design by G3SEK that Donn pointed me too.   You can find 
it at http://www.ifwtech.co.uk/g3sek/dx-book/sequencer/index.htm .   The design 
is based on using a 6 vdc (in my case I used a 5 vdc) DPST relay coupled with 
a series R and a parallel C time constant, and a 12 vdc DPST relay.   The IF 
rigs PTT line controls both relays in parallel .... for my design it looks 
like the two relays together are around 150ma of current sink which should be OK 
as the spec's for my IF rig allow up to 500ma.  The RC time constant around 
the 6 vdc relay provides a slow ON and slow OFF while the 12 vdc relay provides 
a fast ON and fast OFF.   Its then just a matter of connecting one pole from  
each relay in parallel to control the antenna relay (fast ON and slow OFF) and 
one pole from each relay in series to control the 6 watt amp Vcc (slow ON and 
fast OFF) .... basically relay "AND" and "OR" logic.   

The advantage is that the design is very simple.   You can wire the relay 
poles for whatever job you need (ie; sinking, sourcing, voltage differences, 
etc.).   The disadvantage is that the relay contact are controlling the 2.5 amps 
to the 6 watt amplifier so the relay needs to be well rated for this task and 
contact pitting may be a longer term reliability issue .... on the other hand 
we are talking about maybe a couple of thousand makes/breaks a year (?) and I 
can alway replace the $5.00 relay.

So, in theory, I'll be QRO on 10 GHz next year !   Again, thanks to everyone 
for their suggestions.
   
73, Jon
W0ZQ


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