The SWR/Range unit is in a second small aluminum box. The RF is piped from
one box to the other via a pair or right angle BNCs and a female/female
straight adapter. There is a good picture of this same set-up in the article
if you look closely. If you want to see my setup, I can email you a picture.
You want to know if it works?
In a word...yes. I can see those transmitted sine waves as clear as day. I
can see distortion, and I can see when the little 38S trimmer is set to give
me a clean signal. It works. And, once that bridge is properly balanced, I
expect I will be able to use the scope to tune my antenna tuner without
putting a signal out on the air--that is possible with this unit, as it can
use the bridge without putting a signal on the antenna--it goes into the
dummy load.
If one were so inclined, the system could be used to trace signals--though
that would be somewhat more clumsy than with a modern full-bandwidth scope.
(And you would need another signal generator.) But as a dedicated station
monitor to see things like keyed waveforms, output signals, and even voice
envelopes, it works adequately. Since I recently bought myself a 100mHz
scope, I won't use the adapter system for troubleshooting. I have left it
permanantly in line as a station monitor--it fits nicely on one of my
operating desks without displacing too many other things. My Navy OS-8
oscilloscope is quite small in comparison to most scopes of its era--actaully
it is much smaller than my TEK 565! Note, this system would not be useful
for rigorous testing requiring a calibrated scope. For that, you do have to
spend the hundreds.
So, if you have a beat up old working scope, you CAN see signals in the HF
spectrum with it by building yourself an adapter like the one in 73. And if
you have a signal generator, you can do the whole thing for very little
investment. Even if you buy everything at RS and have to pick up an MFJ 207
used, you can do it for less than 50-60 dollars. That certainly beats
spending hundreds for a scope if you only need it once in a great while for
non-critical signal scoping. Incidentally, the adapter in all recent
handbooks is similar, except you would have to apply a variable signal (LO)
to the mixer input at the cap where a fixed xtal controlled oscillator is
applied in the handbook version. In fact, the mixer in the handbook is a
much better device, so that system may even work better.
In all, this was a very worthwhile project, and I plan to leave it up and
running in the shack. It will handle my Yaesu at 100 watts (I do run that
much power when I am trying to do SSTV) and it doesn't seem to be stealing
any significant signal into or out of the station.
72,
Preston WJ2V
Meantime, the Steve Weber Spectrum Analyzer Adapter is 3/4 finished. Stay
tuned for more scope stuff.
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