When your coax is "hot" with RF, there are normally two causes:
1. Feeding a balanced antenna (your loop) with an unbalanced line
2. Radiation directly from the antenna back to the coax.
I suspect you have both happening. The first thing to try is make sure
the coax comes away from the loop at a 90 degree angle, as close as
you can get it. This helps with #2. Secondly, install a choke-type
balun at the antenna feedpoint. This corrects the unbalance situation.
But before doing either, be sure you have a short, direct connection
between the chassis of your computer, your TNC and your radio chassis.
Without that, all your wiring between computer and radio becomes a
small loop antenna itself. Connecting the ground wire shorts out the
loop. Along these lines, be sure the computer and radio power supply
are plugged into the same AC outlet. Having them plugged into
different outlets also creates a small loop antenna.
Good luck and keep us posted.
73, Bill W6WRT
------------ ORIGINAL MESSAGE ------------
On Tue, 1 Jan 2008 07:44:48 -0500, Phil Sussman <email@example.com>
>In an attempt to get back on RTTY, I've been able (thanks to the
>many fine people on this reflector) to interface by TNC to my
>rig, a JST-245.
>By necessity my shack is on the second floor and I am currently
>using a long wire antenna (175 feet) and an old (AEA-3000) tuner.
>Everything loads up fine and I am able to work SSB without any
>difficulty. RTTY is another matter. Every time I key up, the
>station locks up... the computer freezes, the TNC has to be
>turned off, reset, and reinitialized.
>I attributed this to an excessive amount of RF and toward that
>end I built a small RF sniffer using a 50uA meter and a few
>parts. Needless to say I have a real RFI problem. Even at low
>power of about 5 watts, the sniffer meter pegs. I've got about
>20 feet of RG-8 that I use for a 'feed-line' and the radiation off
>the shield is fantastic.
>I attempted to remove the RG-8 and hook long wire directly to the
>tuner. That reduced my radiation by about 20%, but did not solve
>my problems. I installed a 'counterpoise' ground system and loading
>is sharper, but the problem remains.
>Oddly, in SSB operation, the radiation is inconsequential. Only when
>I run RTTY does the duty cycle cause a radiation problem. Also, I've
>noticed the radiation builds quickly after 5 seconds of operation
>from little, if any, to excessive.
>CW causes no troubles.
>My thought is that I need to 'move' the RF away from the rig and
>hopefully into the antenna.
>Any assistance in this matter would be appreicated.
>de Phil - N8PS
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