[R-390] Loop antenna details

[Leigh Sedgwick]

There is a 160 meter receiving loop antenna with pre-amp in this months QST 
of similar construction.  Yours sounds a bit more simple....would be a fun 
project to fool with.  Thanks for the details.

73 de Mike
K7PI


----- Original Message ----- 
From: "Tim Shoppa" <shoppa_r390a at trailing-edge.com>
To: <r-390 at mailman.qth.net>
Sent: Tuesday, June 06, 2006 3:21 PM
Subject: [R-390] Loop antenna details


> Several have already written asking for details of my loop antenna.
>
> Very simple:
>
> Get one ten-foot length of 1/2" copper pipe.
> Also 2 copper 1/2" elbows, one copper 1/2" Tee, and one PLASTIC 1/2"
> elbow. (Not sure exactly about the sizing of the plastic elbow - it's
> the one that 1/2" copper pipe fits into snugly.)
>
> In principle I suppose you could use any sort of small diameter pipe
> or conduit.
>
> I use twinax that I bought for a couple of bucks on E-bay for
> the lead-in. Twinax sometimes shows up in large quantities if you
> watch mainframe computer deinstallations.
>
> Cut the ten-foot length of pipe into 4 equal pieces.
>
> Lay out the 4 pieces on the floor like a diamond. At the top
> put the plastic elbow. At the sides put the copper elbows. At
> the bottom put the Tee. DO NOT SOLDER or securely fasten
> any of the corners yet, if you do so it'll be very hard to run
> the wire inside the copper pipe!
>
> The copper pipe is there to provide electrostatic shielding (it'll
> be hooked to ground) and the plastic elbow at the top breaks the
> circuit (so it is not a magnetic loop).
>
> Run some insulated wire around the loop one or two or three times
> and have the two ends come out of the Tee on the bottom.
>
> Run twinax from the 390A's balanced antenna jack to the antenna.
> Center two conductors go to the loop of wire. The shield goes to
> the copper.
>
> It has some directionality and works from BCB up through at least
> 20MHz pretty well. It is NOT nearly as sensitive as a random longwire
> strung out for even a short distance. But it does an excellent
> job of suppressing household RFI (mostly computer monitors and
> AC blower motors) that plagues my location.
>
> The directionality isn't awfully strong in the "forward" direction
> but there is a sharp null to the sides. My antenna just sits in
> the attic and I try pointing it in different directions every once
> in a while, but I suppose you could add some supporting structure
> (wood? plastic?) and put it on a rotator.
>
> I experimented with different numbers of turns and also with adding
> a resonating tuning capacitor and while there was some difference
> it was not profound. There are several sites on the net that
> talk about similar construction loops and they found for transmitting
> at least that the resonating capacitor was essential.
>
> I suspect that those who are not as plagued by computer and blower
> RF hash as I am will not get much advantage from the loop over a
> random longwire. But for me it's the difference between a million
> screaming banshees and clarity!
>
> Tim.
>
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