Another magnetic loop

[Robert E. Seastrom]

I just worked a guy in Alabama the other day on 20m SSB with 50 watts
into a cross-connect wire loop on the ceiling of my apartment, matched
by an SGC-237 hanging on the wall.  It's 2 turns, about 10' on a
side...  both conductors in parallel which by my calculations means
we're looking at right about 2 ohms of resistance.  Clearly less is
better, but I don't know how skin effect and ohmic losses interplay,
and how much I win going with fatter wire (or even just a single turn
like they recommend in the manual) vs. being Just Screwed by being
indoors, and that's not even counting lumped inductance from where it
crosses the heating vents etc.  Time to experiment, I think.  I don't
think EZ-NEC countenances this kind of bad config.

Bummer that it gets into the stereo system and makes the computer
freak out if I am running more than about 20 watts.  I'm probably in
excess of RF exposure limits but conveniently like most folks here I
got my first ticket before there was a section on RF safety, so I'm
grandfathered.  I only wish I'd thought of this when I had the idiot
upstairs neighbors who insisted upon playing Guitar Hero at 2am.

I've really liked the SGC tuners ever since learning a couple of
important points about them:

1) They don't like crappy power.  If you let your gel cells that run
them run down, or connect them up with kludgey connectors, they'll get
unhappy when they are drawing a non-trivial amount of juice to chatter
the relays.

2) The instructions say that you can just start talking in SSB and
they'll adjust accordingly.  This does NOT mean that if you're running
PSK you can just key-down (or worse, switch to RTTY or CW mode and hit
PTT) and dump a full 40 or 100 watts of carrier into a mismatch.  The
tuner will get unhappy at *that* too.  If you're not running the
little box that makes it emulate an AH-4 (I got mine from
http://www.ham-kits.com/Tuner1.htm ), you need to get one of the "tune
control" boards that lets you just hit the button, as dialing down to
10w to tune and then back up again is cumbersome.
http://www.betterrf.com/

-r

Tom Azlin N4ZPT <tom at n4zpt.org> writes:

> Thanks Rob,
>
> That might be a good option then for Iain. Having some photos would
> help!  I did find that DX Engineering still sells the small MFJ loops
> and MFJ loop tuners for larger loops claiming a 28 ft long piece of
> wire looped can be matched on 60 meters.
>
> http://www.dxengineering.com/Parts.asp?ID=4078&PLID=347&SecID=174&DeptID=55&PartNo=MFJ-1788
>
> http://www.dxengineering.com/Parts.asp?ID=4477&PLID=347&SecID=174&DeptID=55&PartNo=MFJ-936B
>
> 73, tom n4zpt
>
> On 5/9/2011 8:25 AM, Robert E. Seastrom wrote:
>>
>> The guys who make the Turbo Tuner (emulates an icom ah-4 for tuning
>> screwdriver antennas) make a 3' loop antenna.  No idea if it is as
>> finely made as this puppy as there are no pics.  Looks like it doesn't
>> have that gorgeous trombone capacitor; they talk about plates.  On the
>> other hand, pushing a button and having the Right Thing happen has its
>> appeal.
>>
>> http://www.n2vz.com/loop.htm
>>
>> -r
>>
>> Mike O'Dell<mo at ccr.org>  writes:
>>
>>> I'd pay real cash-money to buy one of those already made
>>>
>>> 	-mo
>>>
>>>
>>> On 5/7/11 10:08 AM, Andre Kesteloot wrote:
>>>> http://www.qrpbuilder.com/downloads/loop%20antenna%20110310.pdf
>>>>
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