[Amps] I answered it.

[Jim Thomson]

Date: Sun, 30 Jan 2011 04:40:52 +0100
From: "DJ7WW" <dj7ww at t-online.de>
Subject: Re: [Amps] I answered it.
To: <amps at contesting.com>
Message-ID: <1PjO9m-12vSxE0 at 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