I'm not sure about a mag loop inside a room, I've never tried mine that
way. When used vertically outside, they tend to be insensitive to
surroundings [trees, ground, you sitting under it] because the
permeability of most such surroundings is 1. This may not be true if
you're set up on the track of a railroad yard ... or if there's a lot of
ferromagnetic material in your walls.
If you try it, be aware of several things:
1. Small magnetic loops involve some very high voltages and circulating
currents, even at surprisingly low powers. AA5TB has an on-line
calculator and there is a similar one at
http://www.66pacific.com/calculators/small_tx_loop_calc.aspx
2. The equivalent radiation resistance of small loops is
extraordinarily low -- in the milliohms range. Your power will be split
between the radiation resistance and the RF resistance of the
conductors, which is higher than the DC resistance because of the skin
effect. You really need to achieve the lowest possible RF resistance
[high conductor surface area].
3. Mag loops are resonant transformers or autotransformers. To radiate
at all, they MUST be exactly resonant at your TX frequency. "Getting
close and letting the ATU match it" will create a fairly effective dummy
load. Bypass the ATU and tune the loop for exact resonance.
4. The usable bandwidth will be very low [i.e. you need to re-resonate
the loop when you QSY, even a little]. As the circumference of the loop
becomes smaller in relation to the wavelength [i.e. on lower frequencies
for a fixed size loop], the BW can become smaller than the occupied BW
of a SSB signal.
Commercial mag loops [e.g. my Alexloop] are usable from 40 up. Tuning it
on 40 is really touchy. It's easier on 20 and up. They tend to run in
the $400 range. You can build one much cheaper, but remember #2 above.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 1/22/2017 6:16 AM, Robert 'RC' Conley wrote:
Guys;
I'm anticipating a move to a seniors villa and I know I will be unable to
to take my antenna farm and most of the ham shack. I've decided on my KX2
with ATU (grab-n go). A MAG LOOP should allow indoor operations at QRP
power levels.Thanks for your thoughts.
73
KC5WA
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