Date: Sun, 30 Jan 2011 04:40:52 +0100
From: "DJ7WW" <dj7ww@t-online.de>
Subject: Re: [Amps] I answered it.
To: <amps@contesting.com>
Message-ID: <1PjO9m-12vSxE0@fwd09.t-online.de>
Content-Type: text/plain; charset="us-ascii"
It is more then likely that those on a city lot who crank their power output
way up will run into trouble with their neighborhood.
73
Peter
## I don't have any RFI / TVI with my own stuff in the house and no
neighbors' bitching..yet.
A buddy had severe RFI with his 80m ant... and big QRO. Turns out the
scramble wound
'balun' made from coiled up 213U is not doing the job. He literally wiped
out everything in his house,
including the DSL line.. [ which already had TEN ferrites on it]. The quick
fix was to install aprx 20-30
large type 43 beads [ 1" OD x .515" Id x 1.125" long] slid over the 393
coax..which plugs into the back
of the 10 kw amp. ZERO RFI /TVI after that. None.. it's like there was no
RF present. The 80m
mickey mouse scramble wound balun is still in place for the winter. Another
friend had a similar problem
on 6m..with 5 kw output. It distorted his TX audio. 6m ant had a lousy
designed balun [ new from M2].
Slid 2 x doz type 43 beads over the coax on the back of the 6m amp..and zero
rfi after that.
## No RFI /TVI problems on any other band..except 80m and 6m. And those
were the two bands that had
piss poor [ imo] designed baluns. Mr Brown is correct. With a properly
designed balun.... it will eliminate a whole
bunch of problems. This spring/summer, I will install new type 43 bead
baluns [ large type] on all the yagi's and also 80m
rotary dipole. A type 31 toroidial RF isolator [ has connector's on each
end] will be installed at the INPUT of the remote
switch box [ which is installed on the mast]. A 2nd line isolator will be
installed just inside the basement, bolted to the SPG
[ large 1/4" thick AL plate]. Both line isolator's are in 3/16" thick nema
box's..with all type 31 torroids suspended dead center
inside each box. [ minimizes stray C] The spg plate will have either a
LP-filter, then lightning arrestor, then line isolator...
OR a line isolator, LP filter, then lightning arrestor. The line isolator
can't be installed between the LP filter + lightning arrestor.
if it is.. any common mode RF will simply conduct around the line
isolator..via the AL SPG plate. [ via the connectors on the metal
box's of the lightning arrestor + LP filter..which are bonded to the AL
plate].
## I'm now 95% convinced that most of the RFI /TVI problems are caused by
lousy common mode rejection..due to lousy balun
designs. That and ant's being mounted way too low. Get em up 70' or
more... and most problems will be greatly reduced....
VS the same yagi @ 40' ...esp on city lot's. Without enough common mode Z...
you end up with loads of RFI problems,and Rf getting into the
chassis's, and 3 rd wire [grnd wire] on most gear..then it migrates into main
200a panel, then all over the house, into the street...and all over the
neighbourhood. You can see this effect with clamp on RF ammeter's. The RX
noise level will also increase with poor balun designs.
later... Jim VE7RF
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