----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Sunday, January 30, 2011 6:41 AM
Subject: [Amps] I answered it.
> 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
Ive been 100% convinced of that since the 60's with the Hi Gain BN-88 POS.
Back then a coil of coax worked better than nothing. With decent size
ferrite beads (RG-213 size) becoming available in the early 80's common
mode problems could be solved and phasing lines worked as they should. Using
balanced feeds on yagis also helps reduce RFI when backed up with a coax
balun and sleeve ferrites. I had poor performance on the first 4el 40M KLM
using their 5KW "balun". I threw it off the tower from 160' and used a huge
coil of RG-11 plus beads. Results were a better pattern, SWR bandwidth, and
no more setting off a neighbors alarms. When the second KLM went up at 60'
it used the same setup. M2 bought KLM and still dont have a clue how to
build feed systems. Guys running 6M EME with M2 crap are using fiberglass
support booms when stacking antennas horizontally and then have to drop the
coax vertically to keep from distorting the pattern. Guess they never heard
of dropping the antennas down 4' on a stub mast and using an aluminum
support boom as a tie point for Phillystran antenna boom tie points.
I also use sleeve baluns between rig and LPF and more out of the amp into
its LPF. The reason is to keep RF going thru the filters and not around. Im
99.9% RFI proof in the neighborhood.
Carl
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|