>Our measurements on popular xcvrs over the past 10 years or so (e.g.,
>TS-940, TS-950S/SD/SDX, FT-1000D, IC-781) found the shortest delay between
>T/R relay external contact closure (to actuate the amp T/R) and output of
>initial RF to be ~7 ms. If I remember correctly the 950 was much longer.
>
? Owners of FT-1000Ds have reported seeing RF output at 5mS.
FWIW, my resent measurements of three popular transceivers are as follows:
TS-950SDX -- 15ms
FT-990 -- 10ms
FT-1000mp -- 8ms
Unfortunatley, the FT-990 does not activate the T/R line until 7.5ms after
key closure, leaving only 2.5ms for the amp's relay to close! Further, this
rig cuts the full 10ms off the CW waveform, resulting in very
choppy-sounding CW in QSK mode and first-element clipping in VOX mode. This
becomes noticable above 20WPM and gets worse as the speed is increased. My
measurements agree with those that appeared in QST when the 990 was first
reviewed. Bottom line, unless you use it with a PIN diode amp, safe
switching with the 990 requires either an amp with built-in T/R sequencing
(Alpha, Ten-Tec, Amp Supply, to name three) or an external sequencing
circuit. You have to add some weight to get rid of the choppy sounding QSK
and first-element clipping. You can do that with a keyer or there's a neat
interface box described in the April 1987 issue of QST that will take care
of both the sequencing and weight.
The 950 and 1000mp activate the T/R line immediately upon key closure, and
should be suitable for use with a vaccum relay amp. The 950 chops about
2-3ms off the waveform, which is not audible to me. The 1000mp doesn't chop
anything off. In fact, it looks like the 1000mp might even add a ms or two.
BTW, the 1000mp has the cleanest waveform of the three. Rise time is about
3-4ms and decay time is less than 1ms. Top and bottom are straight as an
arrow. The 950 rise time is adjustable from 2-8ms, but there's visible
overshoot. As I recall, decay time was a little slow but not too bad. There
was a little ripple on the top and bottom of the waveform. The 990 has a
rise time of about 1ms (very fast!) and decay time of 3-4ms (kinda slow.)
Small amplitude square waves cruise across the top and bottom of the
waveform (poor regulation or RFI in some switching circuit?)
BTW, I've not gotten any of Dick's messages on this subject from the
reflector. I'm only getting them as quoted in Rich's replies. Are they being
sent to the reflector?
73, Dick WC1M
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