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[RFI] Tvi Problems

To: <rfi@contesting.com>
Subject: [RFI] Tvi Problems
From: EDWARDS, EDDIE J" <eedwards@oppd.com (EDWARDS, EDDIE J)
Date: Wed, 1 Nov 2000 10:36:19 -0600
> -----Original Message-----
> From: Michael D. Brown [SMTP:mdbrown@iquest.net]
> I'm having some tough tvi problems of late. And I am on cable.  
> We live on a small (120x50) city lot, and my dipole and TH3 are only up at
> 40 feet. The dipole is a 40/80/160 W9INN dipole. 
> The biggest problem is on 80 meters. Even at the lowest power setting on
> my
> TS 850 (10 watts or so) I still get some cross hatching on both tv sets. 
        Hi Mike,
        In addition to the Palomar guys recommendation, I'd add to be sure
to add ferrites to ALL cables into and out of the TV set.  Stop the RF at
all paths.

        Also a higher tower might help too, but that depends on your
circumstances and city's ordinances among other variables.  Probably not a
good option, but one to keep in mind if possible.

> RF chokes (6" diameter, 12 turns) were put on both the TH3 and the dipole.
> I might have gained a bit on the TH3. I can run about 300 watts with it
> before
> I start having TVI problems. But, the amp is an LK 500zc, so I'd rather
> run
> it a bit harder of course. I don't think grounding is an issue. The tower
> is
> grounded, and I have another 8ft ground rod right outside the shack and
> I run #4 solid into the shack, then tie to it with 2" flat braid that goes
> to the
> 850, the LK 500 and the ATR 30 tuner. 
        The tower and shack ground systems should be tied together if they
are reasonably close together.  From the sound of it they are close since
it's a typical city lot.  A single point ground system should be
established.  Go to www.polyphaser.com and click on technical literature.
There's a whole library there.  Find the Ham related info on grounding.
Also the cable TV ground should be tied to the single point ground system if
possible.  Same with TelCo & AC grounds.  This is today's standard in the
comm industry mostly for safety & lightning, but it'll help the "RF" aspects
of grounding as well as long as leads don't get too long.

        Oh yea, get rid of the braid!  It's a possible IM generator which
could cause or add to RFI problems!  Use either copper strap (sold by
polyphaser & others) or a number 2 or 4 stranded and tinned or with green
insulation or tape to identify it as ground wire.  Again, latest comm stds.
> I have put both legs of the dipole out back and it does help quite a bit
> with
> TVI.  But with the lot only being 50 ft wide I see a noticeable drop in tx
> and
> rx when I go that route. I guess if the lowest band I wanted to use was
> 40,
> I could do that pretty easy. But....  
> So far, I have tried winding the excess CATV cable into a fair sized
> choke,
> no luck there. I have a couple of small ferrites, no luck there either. I
> did 
> read on the Arrl page that a company sells (I assume much larger then I
> have) ferrites that you put 15 turns on, and that is supposed to help. 
        The more turns the better; it's almost logarithmic the increase in
attenuation you see with greater numbers of turns.
> The cable tech did try a high pass filter at the tv today. No luck there.
> I
> have a brand new high dollar low pass filter that hasn't helped either. 
        Some are better than others.
> I hope this isn't too much info at once. I feel like I have written a book
> here.
        Never too much info.  Better than not enough.
        Also keep in mind the rusty bolt effect as an external IM generator.
Look for any metal-to-metal contact that has some corrosion, e.g. gutters,
storage shacks, etc.  Especially in the vicinity of the TV set.  

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