Some further investigations: Only a problem on 20M. 15 is actually
fine. so I'm suspecting the RF on the coax problem Bill suggested. The
antenna does have a palomar choke on it at the base of the antenna
transition line. It is a 40meter Windom tho..so 40 and 15 are resonant
conditions for it. 20 is not and I "force" it to work via the tuner.
everything is common point grounded now, snap on suppressors on every
line altho I too suspect they aren't nearly as effective as the full
toroid with wraps. I'' next try getting some of them and add another
choke to the line. So for now, no RTTY on 20M HP.
Thanks Guys.
Curt
KU8L
Bill, W6WRT wrote:
> ORIGINAL MESSAGE:
>
> On Fri, 20 Feb 2009 17:13:48 -0500, Curt Nixon <cptcurt@flash.net>
> wrote:
>
>
>> I took my linear out of mothballs today in the hopes of gaining a few dB
>> on rtty. The soundcard and interface are creating feedback from the
>> linear so it all becomes unstable and not usable.
>>
>
> REPLY:
>
> I had similar problems here and three things fixed them:
>
> First, have the transceiver and the computer sitting next to each
> other so you can run a short ground wire between the two chassis. All
> of your audio cables act as a short antenna with the transceiver at
> one end and the computer at the other. Adding the ground wire shorts
> the ends of the "antenna" together.
>
> Second, install a powdered iron toroid on each cable going into the
> computer - keyboard, mouse and audio cables in particular and possibly
> the AC cord. I originally tried ferrite clamp-on chokes but they did
> no good at all. Powdered iron toroids cured the remainder of the RFI.
> Use ones large enough that you can wrap a half-dozen or more turns
> around each one. I used mix #6 from Palomar in the T-130 size for the
> smaller cables. You will need a larger size for the AC cord.
>
> Third, if you are using coax to feed your antenna directly you will
> almost certainly have RF on the outside of the coax. Install a
> choke-type balun somewhere in the coax, preferably at the junction of
> antenna and coax, but if that is not practical, break the coax
> somewhere before it comes in the shack and install the balun there.
> The idea is to keep the RF current on the outside of the coax out of
> the shack.
>
> With all three measures in place I can run 1500 watts on any band and
> have no RFI at all. All my antennas are within 50-100 feet of the
> shack.
>
> RFI can be very vexing. Good luck.
>
> 73, Bill W6WRT
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>
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