Another magnetic loop

[Tom Azlin N4ZPT]

Hi Rob,

You are likely fine on the RF exposure limits but I also had the same 
experience on computer interference. Both with a dipole strung out under 
the main floor deck (20 ft from my operating table) and an end fed 80m 
dipole with the end hooked to an old RF communications antenna coupler 
on my radio desk. My 10 meter dipole strung just above the roof ridge 
however did not set off my smoke alarms. Had that problem once as well.

I have a bigger vertical diamond shaped wire loop made using a 33 ft 
fishing pole plus two 16 ft poles as spreaders. That one worked fine for 
portable operations at parks and at a VWS island event.

73, tom n4zpt.

On 5/9/2011 11:03 AM, Robert E. Seastrom wrote:
>
> 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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