[Elecraft] magnetic loop antennas

[Ron D'Eau Claire]

As an alternative to copper pipe, you might consider copper foil. RF flows
along the surface of the conductor so it matters little how thick it is. You
might take something like PVC tubing, form it into the required loop, and
cover it with copper foil. Just be sure you use a single piece so you don't
have to "splice" it anywhere around the loop that would require the RF
currents to cross the splice. You might get away with a soldered seam
running all the way around the loop but I suspect the solder wouldn't do
anything. Just be sure the copper overlaps along the edge. Use tape or
ty-wraps to secure the copper. 

Next to the ohmic losses in the loop itself, the majority of losses in loops
is in the junctions connecting the loop to the capacitor and in the
capacitor itself if it has a sliding contact to the rotor.

73, Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Vic K2VCO
Sent: Monday, May 20, 2013 7:07 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] magnetic loop antennas

I googled 'flexible conduit' and what I see looks like BX cable -- made out
of a single flat piece of metal wrapped in a spiral shape. If this is what
you are talking about, it would be AWFUL for this purpose -- it would have a
very high RF resistance and so be very inefficient. There are very high
currents in the loop and you have to keep the resistance at RF as low as
possible -- that's why large-diameter copper tubing is good.

Do you have a link to a picture of the stuff you are looking at?

On 5/20/2013 6:43 PM, Bill Blomgren wrote:
> I saw the great writeup on the magnetic loop antenna and the inventive 
> High Voltage capacitor for tuning the thing. I'm looking at one of 
> them strictly because I'm stuck in an apartment.
>
> The fact it should be good for 100 watts is perfect for what I'm looking
at buying.
>
> I'm just wondering about the copper pipe used for the outer loop... I 
> spotted some very reasonably priced flexible conduit that could be 
> used for the "loop" proper.  Do what is necessary to bond the 
> capacitor into the rig, and it would appear to be a reasonable 
> alternative to the rather pricy copper pipe. (They want your first born
here for that, and the thieves are busy collecting anything that isn't
nailed down.
>
> Thoughts on that for its larger diameter, which should help with the 
> coupling to the rest of the world...

--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/