[IRCA] Coax

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

I think I found why I was unable to null two of the large copper loops
spaced a couple hundred feet apart.  In a word, coax.

I was using the cheap Radio Shack coax, mostly because it was quickly
available.  Bottom line is that the coax shielding is so "leaky" that it
allows unwanted signals in.  This trashed the nulling effect with the two
loops.    My next purchase is some quality stuff with acceptable shielding.
I like RG-6, but not where it will be installed and removed in temporary
use.  The solid center conductor is usually steel, and prone to fatigue
cracks and breaks in time.

Here's what I did to test it.  I used the Palstar receiver in the truck, and
set the selector switch to an empty position.  Tuning across the whole AM
band brought zero detectable signals, even through the two RPA-1 preamps in
series.  This was better than I expected.  Next I ran out a 150' length of
the coax in a straight line in my yard, terminated at the end with a quality
50 ohm dummy load.  I tuned across the AM band again. In many cases the
signals were better on the terminated coax than on either the 5.5' whip or
either of the two 32" loops in the back.

Some significant directionality was noticed on the coax, even on the low end
of the band.  For example, WMCA-570 was inaudible on the coax, but good on
the whip.  The reverse was true on WTAG-580.  At the higher end, 1350 was
WINY as expected on the whip, but the coax had that way down and something
else in there.  740 was likely Boston on one, and NY on the other.

Andrew Corporation makes a coax called Radiax that is intentionally leaky,
so a controlled portion of the signal leaks out per specific length.  This
is used to provide coverage in tunnels and concrete buildings.  To my
knowledge, this effect has never been used for receiving.  I will take the
350' of RS coax I have and a termination and roll it out in an open area
when I get a chance.  Then do a bandscan, and take note of the meter
readings.  Then I'll switch ends with the receiver and termination and do it
again.  It would be interesting if it provided a BOG effect without having
to mess with grounds.  Just roll out the terminated coax in a desired
direction, and away you go.

Anyone else ever try this?

Craig Healy
Providence, RI

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