On Apr 24, 2014 11:50 PM, "Rick - DJ0IP / NJ0IP" <Rick@dj0ip.de> wrote:
>
> One addition to what Stuart has written.
>
> Though we would like to have as large of magnetic loop as possible in
order
> to get good performance on the low bands, large loops do not work well
> indoors. The need to have a distance equal to their radius away from the
> floor, walls, or ceiling. This effectively limits the loop's size to about
> one meter (3 ft.) in diameter.
>
> I had a very expensive commercial loop which was 1.7m in diameter.
> I could get it to work halfway decent indoors on 40m but it just would not
> find a good match on 80m.
> I moved it to the balcony, pushed it up such that it was above the edge of
> the roof a little and it worked great on all bands. Much better than when
> indoors.
>
> Then I moved it to the front yard and raised it such that its lowest part
> was 10 ft. in the air.
> I compared it to a 40m dipole (40 ft. up). There was basically no
> difference, except for some stations, I could rotate the loop and then it
> was a few S-units stronger than the wire dipole.
>
> Don't jump to any false conclusions. My bet is, most loops do not work
like
> they should due to poor construction techniques. You have to use the best
> quality of parts and take much care to keep the resistance between various
> components as low as possible. Otherwise the loss will be too great.
>
> If you open the MFJ mag loop, you'll see that its variable capacitor is
> wielded to the aluminum loop. That's the best way to keep the losses low.
>
> For 80m indoors, I would suggest a 2 or 3 turn loop. 40m works best with
a
> 2 turn loop. It will also work on 40 with a single turn loop, but not as
> well.
>
> One of the guys in my local club lives in a townhouse in the city, with a
> postage stamp size back yard.
> He bought a VERY expensive commercial loop ($1700) and mounted it about 10
> ft. high on his patio.
> His results have been nothing but astonishing.
> He is as loud as anyone else running similar power, all over Germany.
>
> Again, if you can place it outdoors, it will work a lot better.
> But indoors it will be better than other wire antennas or sticks, "if" you
> build the loop with low loss.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Stuart
> Rohre
> Sent: Thursday, April 24, 2014 11:25 PM
> To: tentec@contesting.com
> Subject: Re: [TenTec] New Jupiter on its Way _ A Few Questions
>
> Based on an article on loaded antennas in the latest QEX magazine from
ARRL,
> I would say a magnetic loop, if larger than 0.1 wavelength diameter, might
> have either the same signal as a loaded dipole, (short dipoles as I
imagine
> you mean), or the magnetic loop will have BETTER signal to noise on
receive,
> which is very valuable in the indoor environment. Gain in the receive, or
> low noise, may be better than more signal on transmit.
>
> Both types of antennas would give better results if placed in an
> unobstructed attic, (wood house), or placed at least, on the edge of a
roof.
> A larger than 0.1 wave loop could be hidden in a fenced back yard, and
even
> put on a pulley system that would raise it up to hang in a back yard tree
> for after dark operations.
>
> Being indoors as now; you are in a cage or cobweb of electric wires,
> possible metal plaster lath, and obstructions from large appliances on the
> other side of a wall. You are subject to causing TVI to electronics
inside
> the home at least, or next door, or the next apartment.
>
> Of all the indoor operating means, the loop offers the best results,
> especially on receive, if shielded, and made of low loss construction.
>
> Use large diameter loop material and low loss connections.
> One of the best loop designs for HF used copper tubing of 1 inch diameter
or
> larger, and was octagon shaped, because angled fittings were available.
The
> joints were silver soldered for lowest loss.
>
> The capacitors on the end can be trombone type made from sliding copper
> pipes, with teflon tape as spacer and insulation. Or use surplus vacuum
> variables which turn up at swap meets. Or even large metal air spaced
> variables. while you might spend some money up front on material,
> (pipe) and capacitors, those parts and the loop can be used for ANY future
> locations, Field Days, or even mobile on a van.
>
> Locally, Bob, WB5AOH had one on his van that worked HF great on low bands
> like 40 and 75. He would still have it but for a low hanging tree limb!
> (With big mobile antennas back in bicycle days, I learned you have to
drive
> both the vehicle and the antenna!)
>
> -Stuart Rohre
> K5KVH
> ____________
I have 15 foot ceilings, so I have a lot of space in which to erect a loop
antenna. In fact it would be much less obtrusive than the current antenna I
am using. I think I am going to inquire about some of the commercially
available loops (isotron, Mfj, etc...)___________________________________
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