Date: Mon, 25 Oct 2010 10:06:53 -0700
From: Jim Brown <jim@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
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