Re: [IRCA] Cable work

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> I'm sure you are aware of Mark Connelly's work in phasing portable
> units.  He uses a roof mounted broadband loop and a whip phased against
one
> another for effective work.  Here's a discussion of his technique:
> http://home.comcast.net/~markwa1ion/exaol1/phased_arrays.htm
> I'd also recommend his other articles in his RF building blocks section.

Yes.  Mark has been in on the conversation, though he isn't on this list
(sadly).  Many of his articles are also hosted off chowdanet.com, which is
another of my sites.  It's for a FIDO BBS I've run for years.

> Curiously, I have not seen in Develdore's Topband antenna book the need to
> shield the impedance transformers in metal boxes nor in Tom Rauch's W8JI
> site.  Perhaps I overlooked it.  These topbanders are pretty persnickity
> when it comes to losses and taking care of details. While toroids are
> self-shielding, they do suffer proximity effect from metal cabinetry, etc.
> These losses are not as serious in an amplified circuit because of Q
> multiplication.  Have you ruled out whether or not the signal attenuation
> you have observed is caused by RF shielding or simply because of Q tanking
> because of proximity effect?  A simple way to determine that would be to
lay
> the transformer on top of the box rather than inside of it.  Good luck.

When I first tried the CAT5 cable, I simply had the BNC, toroid and RJ45
loose.  I did test it again later after I built it into a Hammond box, and
found a slight decrease in signal ingress.  What I didn't do is space the
toroid so it was centered in the box, nor were the windings exactly opposite
to each other on the toroid.  That's been fixed, and will be my next test.
Just waiting for the 'round tuit to come back.

I suppose the best way to test is to use a specific antenna, oriented in the
same way each time.  Terminate the cable and take a set of readings through
the band.  Then connect the cable, and repeat.  Compare the two sets of
readings.  The cable that shows the greatest difference is the winner.

I suppose there are a number of ways to get this done.  Just looking for the
most effective way.  Takes time and money, and there's only so much of each
in the bank.

Another thing I did was to send a link to the article to DX Engineering.  I
had a conversation with one of the folks there, and he suggested I do that,
so..

Craig Healy
Providence, RI

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