I had a couple emails from guys asking about how I measured the switching times
in the amp and exciter.
All relay measurements in amp are made with no filament voltage and no high
voltage. No exceptions, naturally.
I use a 555 timer and a couple
2N2222s to generate a square wave to key the
rig on cw and give me a place
to trigger from. 1 pulse of 160 ms, then 840 ms off.
Then I leave that alone. That trace becomes my t0 (T
zero).
Then I look at the rf out of the exciter with channel B and note that
time
(0-30 ms, adjustable on 1000MP). Just clip the probe on the SO239 connector.
Then I unsolder a lead off the amps
output relay and use a little resistor
and battery so I can see a voltage
change when the contacts operate and
measure that time with channel
B.
Same for the input relay and the relay that operates the bias.
The only
parameter that is easily adjusted in my setup is the time after key
closure
before the RF appears out of the exciter (FT-1000MP). In order,
here are my
results:
T0
T0+2 ms - PTT (amplifier key ) line out of the exciter to
amp
T0+5 ms - amp input relay and bias relays close
T0 + 13 ms - output
vacuum relay operates
T0 + 15 ms (adjustable via menu) - RF out of the
exciter
Summary and "where do we go from here" ------
My amp and
relays are happy with not getting RF drive till T0+15. This may
not be good
enough to prevent chopping of dots in cw, haven't figured that
out
yet.
Efforts could be expended trying to speed up the vacuum. There are
techniques to do this.
Before I discovered the menu that allowed me to
delay the RF by 15 ms it was
outputting immediately which would NOT make
that vacuum relay happy.
Someone told me he had an Icom 756Pro II and it did
not have a delay. This
is surprising and disappointing, if true. Because this is the easy, fast fix.
An
alternative to delaying rf out would be to delay the bias relay in the
amp,
say to 15 ms. I need an education on that matter. If RF drive hit the
amp
at T0+2ms, before the amp rf relays operated, it would initially dump rf
into
the antenna, then 3 ms later into the cathode (assuming G-G) of the amp, then
the
vacuum relay would switch cold, but rf would be going into the cathode with the
amp in cutoff. Then the bias relay would switch and apply power out the vac
relay. All the relays would be happy, but how would the exciter and the amp
feel about having rf go into the cathode with the rig biased off.
Any comments on this?
Rick K2XT
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