Is the beam directly over your shack roof? Is the tower right next to the
house?
My initial thought is that you are probably attracting more r-f into the
shack equipment with all the attempts at "grounding." If you are directly
in the induction field of the antenna, then there will be a strong field in
the shack and r-f voltages and currents will be present. It is borderline
impossible, in my experience, to "steer" all these undesired currents to
something called "ground" in an effort to get rid of them.
The idea which would seem to work best would be to place all your equipment
at the same potential by connecting the units to a common star ground
system in the shack with the shortest feasible heavy conductors. As it is
you place each unit at a different potential by having a different length
"ground" wire to "ground."
Try tieing everything together with the shortest possible leads and then DO
NOT connect your common ground point to anything - and see what happens.
If you still have a problem, you can employ a "driven ground" which is a
1/4-wave wire, open at one end with the other end connected to the common
point of your star ground system. R-f from the antenna will cause the open
end of the wire to attain a high r-f potential - keep it insulated! - and
the end tied to the equipment will be driven to near zero r-f potential.
Use a separate wire for each band. They will radiate so be careful where
you run them, etc.
In no way, however, would I attempt to make any connection from your star
ground common to an Earth ground, a power system ground, or any other
metallic object in the house.
Good name and call!
73/72, George
Amateur Radio W5YR - the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489 Icom IC-765 #2349 Icom IC-756 PRO #2121
George Skoubis wrote:
>
> Hi everyone,
>
> I hope one of you guys can help me fix an RF feedback problem I've been
> having with my Omni VI Opt 3 upgrade rig.
>
> I had been using a vertical antenna but I found myself frustrated with my
> inability to hear many stations so I decided to buy a 3-element beam and a
> tower.
>
> In early July I bought a 50 foot crankup tower and ordered a Fluidmotion 3
> element beam.
>
> I did the negotiating with my wife for my tower placement and the approved
> spot puts the beam 35 feet over my 2nd floor ham shack. I realize this is
> not optimal, but this is what I
> have...
>
> I pounded 4 ground rods in a 8' semicircle around my tower and ran #6 bare
> copper up to my shack coming in through the deck and wall in grey plastic
> electrical conduit. I ran a ground wire separately from each piece of shack
> equipment to the ground wire at the entrance (425 amp, 238 tuner, Omni VI,
> 425 power supply, 12V power supply) to avoid ground loops.
>
> After firing up the equipment I immediately started recieving poor audio
> reports whenever I run the Titan amp.
>
> I wrapped the microphone cord around two ferrite toroids. I put ferrite
> and audio isolation transformers on the audio in and out rca patch cords. I
> disconnected the audio in and out rca cords. I put an isolation transformer
> in the microphone signal path (Heil headset with the DX element). I twisted
> the microphone cord so it spirals like ladder line or twisted pair. I
> wrapped the power cord around some ferrite. I moved the amp, amp power
> supply, and 12V power supply farther away from the radio.
>
> The station interconnects are 1/2 Andrew Superflex with LMR-400 coming
> down the tower and into the shack. I put an extra 3 feet of Superflex
> between the amp and rig and that had no effect either...
>
> I have a 19 inch Viewsonic monitor on a shelf a few inches above the rig
> so I unplugged it to ensure there wasn't a magnetic field problem with the
> rig (this should have showed up at 100 watts also, but I figured I would
> give it a try). I took apart an old computer case and put steel side panels
> above and below the radio to partially block any magnetic fields caused by
> the 425 Titan power supply.
>
> I have hot water baseboard heat (copper pipes) so I tried connecting the
> water pipe to the ground system (no improvement).
>
> I made a 10 turn 6" diameter coax choke and taped it to the antenna boom
> and that didn't help either...
>
> My Omni VI is an earlier one, not one of the later SMT ones...
>
> I'm going to call the factory tomorrow, but if any of you spot something
> you think I missed, let me know.
>
> Replies are welcome direct or through the reflector!
>
> Thanks,
>
> George / KF9YR
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