[Elecraft] Astron RS-35M - Problem Related to RF !!!

[Ron D'Eau Claire]

You got it Mike. True, the antenna does not "cause" the problem, but by
reducing the RF pickup by changing antennas one can make it a LOT easier =
to
avoid RFI issues.=20

My point was that today one can prevent RFI in any well-designed piece =
of
gear - like an Astron power supply - regardless of the nearby RF field. =
And
that I think taking that approach is the best because then it won't =
suddenly
turn up again if something is changed around that once again increases =
the
RF field around the power supply. What I didn't say was that sometimes =
it
can be easier to move/change the antenna than it is to fix the equipment
with the problem.=20

Some gear CAN'T be RFI proofed, or at least would be so difficult to do =
that
it's hardly worth the effort. In my experience, one of the worst in this
regard are powered PC speakers with some telephone answering machines a
close second. The PC speakers I've used have no shielding, no bypassing =
and
use bi-polar transistors that make excellent RF detectors. While it is =
no
doubt possible to RFI-proof them, it might take bypassing the base of =
every
transistor to ground. I never got around to attacking them seriously,
finding turning them off an easier solution for me. Eventually I =
switched to
a notebook computer in the "shack" and the problem went away.

I understand that you aren't complaining about the W9INN antenna. That's =
an
excellent point, and why I'm likely to volunteer such a message as I did
this time.

 I've had people explain to me various antennas are "no good" because
produce they RFI in the shack, etc. My response is "nonsense"...  But =
when
you use different antennas you may have to deal with issues differently. =
One
of the biggest issues in the USA these days are those trying to used
voltage-fed antennas. They REQUIRE good RF grounds at the rig, where =
antenna
systems with a low impedance at the shack end often need no ground at =
the
rig at all. So ops casually trying out a voltage fed antenna, like an
end-fed half wave wire, suddenly find themselves beset with problems =
with
RFI on the rig, etc., and blame the antenna.=20

While changing to a different antenna might fix the problem, it isn't =
really
isn't a sign that the antenna is in any way defective.=20

In your case, that may be what's happening by accident because of the =
high
SWR on your feedline. Retuning the W9INN antenna so it has a lower SWR =
on
the feedline may well cure the problem by reducing the impedance at the =
rig.
If you improved the RF ground at the rig, you may well see the RFI go =
away
too. But, since the W9INN is designed to use a coax with a low SWR, it
sounds to me like you are taking the right approach by retuning it.=20

Ron AC7AC

=20

-----Original Message-----
> No doubt you can change the behavior - even stop the shut-down - by
> messing with the antenna, but antennas do not "cause" these issues.

OK, I'm going to demonstrate my ignorance here but I'm curious about the
phrase that 'antennas do not cause these issues'

I presently have an RFI related issue with a 87' W9INN MPD5 (80-10) =
dipole I
just hung at about 30' across the roof a few days ago. Not with the PS =
but
with a 'hum' emanating from my (powered) PC speakers when I xmit. This =
'hum'
occurs ONLY on 20 mtrs.

We're talking a measly 5-10w out here (no K2/100)

Due to (I suspect) a capacitive effect resulting from a close the =
proximity
to the roof the 20 mtr element is currently resonant around 13.8 Mhz and
thus has a fairly high SWR even at the bottom of 20 mtrs.  The KAT2 =
easily
handles the mismatch but of course a standing wave current is still =
present
on the feedline.  Of course this is unacceptable and I will re-tune the
antenna but in the meantime...

"All things being equal" I also have a Sigma GT-5 that is actually
physically closer to the rig/speakers than the dipole but does NOT cause =
the
speakers to hum when xmitting on 20.  I presume I have no RFI issue with =
the
GT5 due to an excellent 'in band' match.

Since 'one antenna does and one antenna doesn't' it sure seems to me the
(dipole) antenna is causing an RFI issue.  The coax that is likely =
actually
radiating the RFI (?) is just a symptom, the effect of a badly tuned =
antenna
and the antenna is the real source of the issue.  If not the antenna =
then
what?

Reason I ask is I am *assuming* (and we all know what that means) that =
since
I didn't have RFI problems prior to this once I get the antenna properly
tuned the RFI will go away.

p.s. This should in no way reflect badly on W9INN antennas. They are =
really
great. I bought it used and since they are individually custom built I =
am
simply having to 'tweek' it to my particular circumstance/installation.

Mike 'hope to learn something here' K5PU