[Amps] construct ferrite "line isolator"

[Jim Thomson]

Date: Mon, 25 Oct 2010 10:06:53 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
Subject: Re: [Amps] construct ferrite "line isolator"

On 10/25/2010 9:52 AM, tzikas tzik wrote:
> I have problem with R.F interference from linear amplifier or antenna to pll
> unit. I believe that i have ground loops. I have read some relative
> articles:
> http://www.radioworks.com/nbgnd.html
> http://www.airmail2000.com/rfi.htm
> This articles propose to use ferrite "line isolator" between pll and linear
> amplifier (in the coaxial cable RG58) and in the output coaxial cable
> (RG214).
> i have many ferrite beads (material 43) FB-43-7351 and FB-43-1020. How i can
> construct these "line isolatosr".Do you have any schematic? thank you very
> much.

Both of these references are way off base.

I strongly suggest that you study my RFI tutorial, paying careful 
attention to the discussion of "the pin 1 problem" and the discussion of 
ferrite chokes.  In general, ferrite beads are useless at HF frequencies.

http://audiosystemsgroup.com/RFI-Ham.pdf

73, Jim Brown K9YC

##  whoa.  A buddy of mine just installed a  M2 ,2-el 80m yagi  up 190'.  The 'balun' m2 used
inside the DE  relay box is just coiled up RG-393...and not very effective on 80m.   He had loads
of RFI problems in the shack, and knocked off his DSL connection, etc.  I suggested he slide 
24-36  large  type 43 beads  over some FSJ 1/2" heliax... and install  it on the output of the linear. 

## END OF PROBLEM.  Since there is 13 x yagi's on the same rotating tower....and  a hb  1 in, 9 out
remote switch box at base of tower,  by installing the type 43 beads on the output of the linear, the beads are
also used  on all the other bands too.  The large 1/2"  ID  x 1" OD  x 1.125" long beads  were on hand from
another ant project  [160m vertical].  Type 31 large beads woudl have worked better.   Type 31 torroids would
have worked better than the beads, but were not available...and he needed a quick fast fix.  

##  since he can't get at the DE, being way out on  the boom,  the 2nd fix will be to install a 2nd line isolator, located
at the  junction of the 80m boom + tower.   That's all 1/2" heliax going up the tower, on every band.  The 1/2"  Flexible
FSJ stuff is used going out along each boom.  Each yagi is trammed up, with it's FSJ pig-tail..then spliced into the main 
coax heading down the tower.  Ferrite beads were used at the feedpoints  of all the other yagi`s..except the 80m yagi. 

Meanwhile, the  `quick fix`  of 2 x doz+  beads  on the output of the amp  solved all the RFI problems.  Before that, 
loads of ferrite was used on the dsl modems, and everything else.   The real fix was to kill it between output of amp..and input
of remote switch box.  Installing type 31 ferrite torroids, wound with coax will also work,  provided you install  2-3 of em,
in series  to cover the entire 160-10 m bands..with each optimized for either low or high bands.   In most cases,  you don`t need a 
huge Z  to  kill residual RFI problems like this.  My definition of  a line isolator is just a choke balun with coax connectors on each end,
and to be used downstream   from the ant feedpoint itself..to be used to clean up residual RF.  Now if the correct choke balun was
used at the ant  feedpoint to begin with,  you wouldn`t have residual RF problems  in the shack+ house.           

I got around the pin 1 problem ny using a Jensen  JT-11-P1  xfmr... with shielded balanced cable + XLR`s  going into
the pri of the xfmr.... and  a real short piece of RG-59  on the output side of the xfmr.    A new RCA  was installed on rear apron of
yaesu  MK-V chassis itself.   Then a 220uf non polarized panasonic SU series cap,  recomended by Bill  Whitlock,   from hot side of
RCA  directly to the analog BM input.  This bypass`s all the mickey mouse stock yaesu noisy, mic pre-amp stages completely. The
SU cap is required to block DC.  Without it, the BM  will unbalance itself, resulting in SSB + cxr. 

None of my audio rack gear has any Pin 1 problems.  It has to be some pretty old audio rack gear to have Pin 1 problems. 

later...  Jim   VE7RF