On Sun, 2006-05-28 at 14:28 -0500, Larry Menzel wrote:
> I agree, and I suspect you are suffering from some version of "common mode"
> rf interference.
>
> I suggest:
> 1. Make sure your coax does not run in close proximity to your AC lines in
> the shack if possible.
> 2. Make sure if you have other runs of coaxial cable that they're not
> bundled together close to the radio.
> 3. Do you have an antenna rotator? Make sure that line is not running
> directly next to your coax. A couple of turns on a large doughnut toroid
> on the rotator line can be very helpful in breaking common mode
> interference.
> 4. Where your coax enters the shack, form a coaxial balun, about 6-8 turns
> on an 8" diameter and tape or tie wrap it in place. This will help keep rf
> off your coax as well.
> 5. Make sure your amp and all radios and power supplies are grounded with
> separate ground straps to a common tie point and thence to a good earth
> ground...not cold water pipes or electrical system ground. Coax braid works
> great.
>
> You should not have any difficulty running a kw with your Jupiter or any
> other radio for that matter. I have two amps in the shack one on each
> Orion, and run them at 1500 watts out all the time during two radio contests
> without any rfi or rf in my radios.
>
> Good luck.
>
> Larry, N0XB
> Northfield, MN
>
On top of these, make sure your coax has more than 65% braid (typical
from Radio Shack) because that little copper doesn't do good at keeping
RF inside the coax. Good coax costs money and really shields. Good
connectors are soldered on, not screwed on.
Unbalanced antennas like off center fed windoms tend to have more RF on
the outside of the coax than a center fed antenna. Thats because the
antenna is not balanced each side of the feed point.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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