Larry,
Thanks for the concern about the RF levels. I didn't mention in my
note that my antenna is on a short mast on a 50 ft tower. My tower is
right outside my shack window though so I am still right underneath it
although it's at least 38 ft above me.
I used the University of Texas (Austin) RF safety calculator
http://n5xu.ae.utexas.edu/cgi-bin/rfsafety.cgi to calculate my RF
exposure levels. I used an average power of 1000 watts (this is way
higher than a real average power rating 1500 watts X 40% CW duty factor
X 67% maximum transmitting time 10 minutes listening 20 minutes
transmitting = 400 watts), antenna gain of 2.2 dbi (equivalent to a
dipole since it is a dipole from below, the director and reflector focus
RF mainly in a horizontal plane) and an operating frequency of 28 mhz
(the worst HF frequency for RF exposure). The safe distance given by
this calculation is 39.86 feet in an uncontrolled environment and 17.85
feet in a controlled environment.
This is still probably too close for my computer, and I would like to
get the antenna farther away from my shack, but I am on a city lot and
this is where my xyl and I could agree on and stay away from the power
lines.
We just bought 4.5 acres of land at the edge of town and I will be
putting up a larger tower much farther away from the shack when we build
there in a few years (will be a great opportunity for putting in a great
ground system and some nice low band antennas as well) but I feel the
antenna is at a safe distance for now...
I do agree with your recommendation of the Radioworks line isolators,
I have two of them inline as well as one on my 12V line and while they
may be overkill they certainly aren't hurting anything and as long as my
signal sounds good I'm not going to remove them!
Thanks again for the suggestions and sorry for implying that the antenna
was on the roof right above the shack...
73 de George / KF9YR
-----Original Message-----
From: tentec-bounces@contesting.com
[mailto:tentec-bounces@contesting.com] On Behalf Of W1GOR
Sent: Tuesday, May 20, 2003 1:48 PM
To: tentec@contesting.com
Subject: Re: [TenTec] RF Feedback on Omni VI (opt 3)
George,
The very first thing I'd recommend is to move that beam off the roof and
onto a mast/tower as far from your shack as you can go. If you do the
math,
your RF exposure is way above the safe levels... You're just too close
to
the beam and your RF level is quite high due to the 1500 watt amplifier.
You may have kept RF out of the RF equipment, but the computer is
probably
being saturated...
73, Larry - W1GOR
----- Original Message -----
From: "George Skoubis" <george.skoubis@verizon.net>
To: <tentec@contesting.com>
Sent: Tuesday, May 20, 2003 13:48
Subject: RE: [TenTec] RF Feedback on Omni VI (opt 3)
> Hi,
>
> I also have/had this problem and it wasn't RF feedback. In my case
it
> was a ground loop problem.
>
> Disconnect anything you have plugged into the RS-232 port,
Mark/Space,
> Audio In, Audio Out, and Serial Port jacks on the back of your radio.
>
> Transmit and see if your problem is gone. If it is call the service
> department and have them send you a fax of the fix for the TX Audio
> Board ground loop. They will send you a picture of the board which
will
> show you two places to cut the ground foil, you then have to add a new
> ground to two places as well.
>
> This was not a complete fix for me, I still need to wrap my RS 232
> cable through a toroid and cannot use the serial port and RS 232
> simultaneously (I made a Y-cable to split the data signal so the
> computer and antenna controller can both read the frequency data).
>
> I still cannot plug the computer into the audio jacks (without
getting
> transmit distortion) so I cannot use the computer for voice keying.
>
> I can operate my Omni VI Opt 3 with my Titan amp at 1500 watts with
> clear transmit audio (I'm on the second floor, right under the beam)
on
> 10, 12, 15, 17, and 20 meters SSB or CW. I don't have an antenna up
for
> 40-160 right now but I will be trying it out in late fall when I put
up
> a contest-season wire antenna.
>
> 73 & Good luck de George / KF9YR
>
> -----Original Message-----
> From: tentec-bounces@contesting.com
> [mailto:tentec-bounces@contesting.com] On Behalf Of Mark Erbaugh
> Sent: Monday, May 19, 2003 10:35 PM
> To: Tentec (E-mail)
> Subject: [TenTec] RF Feedback on Omni VI (opt 3)
>
> My Omni VI option 3 upgrade has developed symptoms of RF feedback. I
got
> a
> report of RF in my transmitted audio. I'm also hearing muffled audio
in
> the
> speaker or headphones when transmitting. I get this problem even when
> transmitting into a dummy load. The muffled audio in the speaker seems
> pretty much the same whether I'm on 75m or 10m.
>
> My Pegasus is sitting next to the Omni VI. I moved all the cabling
from
> the
> Omni VI to the Pegasus. The Pegasus doesn't appear to have the RF
> feedback
> problem.
>
> My ground isn't ideal. I have about 15 feet of RG8 coax braid going to
> the
> copper ground wire that runs from the electrical panel to grounding
rods
> (2). There is about 8 feet from where the braid joins the ground wire
to
> the
> ground rod. So I guess my total length to ground is about 23 feet.
>
> I do plan on shortening the path to ground and using heavier wire, but
> that's going to require drilling through the poured walls of my
> basement.
> The two ground rods for the electrical system are just outside the
wall
> of
> my shack (about 6 feet apart). By drilling through the basement wall,
I
> should be able to get the total length to the first ground rod down to
> six
> feet or so. Is it likely that a third ground rod for the shack (but
> connected to the other two) would help?
>
> Any ideas?
>
> Thanks,
> Mark
>
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