[Elecraft] Magnetic Loops

[Brian Murrey]

There is a Yahoo group called CW-CODE-WARRIORS that has a ton of data
on building Mag Loops, as well as numerous builders that have had
great success with the antenna from all over the world.  Check it out
if you are interested.

73 de KB9BVN
Brian Murrey




On Mon, Aug 3, 2009 at 2:57 PM, Doug Person<doug at northroutt.net> wrote:
> Just for fun once, I decided to make the smallest possible antenna and
> see if I could make any contacts. I wound about 30 week of #12 solid
> insulated wire around a 3/4" PVC pipe. Parallel to it and electrically
> in series, I created a tunable tubular capacitor using copper pipe and a
> threaded brass rod.  You  screw the rod in to increase C and out to
> decrease.
>
> Using these strictly guesstimations, I found I had good SWR across the
> entire 20 meter band with about 1.7:1 on the edges. I mounted it on an
> 8' aluminum mast which was also connected to the shield side of the coax.
>
> I got on with my little Yaesu FT-840 and in 5 minutes I had a pileup of
> stations wanting an explanation for my report of an 18" vertical. I
> guess the efficiency must have been only a couple of percent.  But,
> there it was, the smallest possible vertical for 20 meters!  I worked
> about 15 countries that afternoon with it.
>
> Doug -- K0DXV
>
> Ron D'Eau Claire wrote:
>> I'd like to be clear when I wrote earlier that a small transmitting loop is
>> very inefficient.
>>
>> I didn't mean they don't work, only that they only radiate a small part of
>> the RF applied to them compared to a larger antenna.
>>
>> Consider a typical mobile "whip" antenna. They're terribly inefficient too
>> but people get out with them, sometimes working DX when band conditions are
>> good.
>>
>> Of course mobiles generally run more than the 10 watts or so a K2 produces,
>> but contacts are made with QRP power and such antennas all the time.
>>
>> One way to make a given antenna "larger" is to use a higher frequency band.
>> It's a matter of the antenna's size in wavelengths or fractions thereof that
>> is important. That's why small antennas do so much better when the sunspots
>> are active and the higher frequency bands are open.
>>
>> Ron AC7AC
>>
>>
>>
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