Thread: Tunable hum in Heathkit SB-401 RF output
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Old June 23rd 08, 12:25 AM posted to rec.antiques.radio+phono,rec.radio.amateur.boatanchors
exray[_3_] exray[_3_] is offline
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First recorded activity by RadioBanter: May 2008
Posts: 15
Default Tunable hum in Heathkit SB-401 RF output
wrote:
On Jun 22, 4:07 pm, "Kim Herron" wrote:
Hi Dave.

Over the years I too have run into the same situation and what the
fellows here are telling you is most likely correct. I can also tell
you the you don't need any antenna to pick up that transmitter when it's
that close. In fact you'll do better if you don't use an antenna or
something very short to get a better picture of what your xmtr sounds
like. This is one time where an RF envelope monitor scope comes in REAL
handy. If you have hum on the transmitted envelope you'll see it on the
scope.
Kim W8ZV

Thanks, Kim. As recommended by another poster, I think the best
course of action is to use an external antenna and make a few contacts
to get signal reports.

You’re right about the monitor scope. There’s a companion Heakthkit
SB-610 Monitor Scope that I don’t have, but could use right now.

-Dave Drumheller, K3WQ

I'm going to be the killjoy for the easy solution. I had a Galaxy 5
with external VFO that did something similar. I forget all the details
but in one of the modes (trcv or rcvr-xmtr or xmtr-rcvr) I got hum
modulation that was apparent on transmit. I could also hear it on
receive without even activating the xmtr.

A previous owner had shielded the cables inside the VFO and done some
other stuff and apparently struggled quite a bit to solve it. I
couldn't resolve it either. I just accepted not to use that particular
switch position.

Gotta be some weirdo ground-looping issue. I know the older Drakes
(twins) were very persnickety (sometimes) about the interconnecting
cable lengths.

If you do figure yours out be sure to post the solution here. I'd be
very interested.

-Bill..

...
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