[IRCA] Dual feed loop

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

I have made an addition to the copper tube loop which I am very excited
about..

Most loops need to be physically tilted to obtain the deepest null.  Without
extraordinary mechanical effort, this cannot be done remotely.  I think I
have overcome that problem.

The normal copper tube loop I have made has a single toroid pickup at the
bottom of the square.  Tonight I added an identical toroid pickup to the top
of the square.  The outputs were then connected to a phasor similar to the
Quantum, or one of Mark Connolly's designs.

By adjusting the phase and level of one pickup against the other, I can get
a deeper null than I have been able to get by tilting the loop.  In
operation, I turn the loop to get the best possible azimuth null, then use
the phaser controls to fine tune the null.  Right now I'm listening to my
nearest local, a 5kw 790 station, being trashed by co-channel stuff.  Since
the 790 is an ancient allocation, every other station protects it to a great
degree.  780 and 800 adjacents are perfectly clear and splatter-free.

Even some stations like WDDZ-550 are difficult to get a good null on, likely
due to local re-radiation.  I can get a better null using the dual feeds and
phasor than by any other way.

When the weather breaks, I'm going to waterproof the two pickups and mount
the loop on top of my tower on a rotor.  I'll have to run two coax feeds,
but so what?  Cable isn't all that expensive.  For years I've wanted a loop
I could mount outside away from the house noise.  I could never get the deep
nulls I needed.  This will do it.

I'll try to get some pictures of this, but it's pretty darn simple.  Even
the phase of one pickup vs. the other doesn't matter as the phaser will
correct that.

Craig Healy
Providence, RI


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