Re: [IRCA] AC twin lead or speaker wire for lead in.

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> I was once told that when you hook up the coax to the receiver and the
> matching transformer, the directivity of the unwanted signals on the
> coax for the most part are a non issue. Once you disconnect the coax
> from the matching transformer or even terminate it, the pick up will be
> heard. Of course going to double/triple  shield or maybe bigger stuff
> (RG213), hardline may solve the issue too.

My question is just where does this signal input come from?  If the coax and
dummy load shielding is good, then theoretically there should be no way in
for those signals.  How do they get in?

My original test was posted on another list, but here's a summary..

What started this was an attempt to phase two copper tube loops.  They were
set in line so each nulled a N/S line, and set in phase.  They were about
200' apart and connected by two 150' runs of new Radio Shack RG-58 coax run
to the phaser.

I then attempted to phase one against the other to try to generate a second
null.  What I found was that the whole setup was pretty much omnidirectional
regardless of the placing of the loops, or any action of the phaser.  I
tried both a home-made phaser and the DX Engineering NCC-1.  Nothing.
Couldn't reduce any signals by any appreciable amount.

I then disconnected everything except one of the coax runs.  It was
connected directly to the receiver and the far end to a shielded dummy load.
With the dummy load connected directly to the radio, no signals at all were
heard.  With the 150' of coax in line, it functioned almost as well as a
BOG.  I first attributed it to the el-cheapo Radio Shack cable.

Next test was to duplicate the testing, but with a brand new run of good
quality RG-6 coax.  Oddly, the results were identical.  This coax was Belden
(good brand name), fresh out of the box, and new connectors crimped on.  At
this point I was rather confused.  Maybe it wasn't "cheap coax" after all.

Next I made an "un-un" which is an isolation transformer with a 1:1 ratio.
I think I had 8 turns bifilar wound on an Amidon FT-87-J core.  Made
absolutely no difference.  Connect the dummy load through the "un-un" right
to the radio, no signal.  Put the 150' of RG-6 in there and it became an
antenna.

I tried several further tests involving various types of grounding,
including driven rods, radials, and even parking next to a known good
ground.  No difference.  Nothing I tried with coax would reduce the
incidental pickup.  This unwanted pickup was spoiling any nulls by
introducing signals of random phase to the antenna.  After the first couple
of hours of trying, I just gave up.  This same receiver/phaser system using
two BOGs of about 450' length produced exceptionally good results, so it
isn't the equipment.  The receiver used is outlined on the am-dx.com site as
my truck installation.

So, today's test that provided some useful signal isolation was a very
welcome bit of progress.  I will build off this to try to improve it.  Next
thing will be to ground other pairs in the CAT5 cable to see if the unwanted
signals can be reduced further.  I also am going to use a couple pairs to
get 12vdc to a preamp at the antenna end.  That will further swamp the
unwanted signals.  Multiple pairs are useful.  And, it is wired using normal
ethernet connectors and configuration.  I can buy a premade ethernet cable
and use that.

After the coax tests, I'm not at all sure that *any* coax would do what I
need.  I should drop a note to Dallas Lankford and run this past him to get
his thoughts.

Craig Healy
Providence, RI

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