Re: [IRCA] 4 Foot Box Loop Plans

[Russ Edmunds <wb2bjh@xxxxxxxxx>]

In extensive testing performed back in the 1970's, it was fairly well determined that a 4' loop would have sharper nulls than a comparable 2' or 3' loop. As Rick states, a balanced loop - whether directly coupled through a pre-amp or inductively coupled via a link coil, offers sharper & deeper nulls, as well as a more nearly symmetical pattern as compared to an unbalanced loop.

The design of the NRC loop offered two different lengths for the main coil, one for use directly coupled with a pre-amp, the other for use with a 2-turn link coil. The difference was, not surprisingly, 2 turns.

What works best depends on space available, local noise, local signals and of course, your needs as a DX'er.

Russ Edmunds
Blue Bell, PA ( 360' ASL )
[15 mi NNW of Philadelphia]
40:08:45N; 75:16:04W, Grid FN20id
<wb2bjh@xxxxxxxxx>
FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'
AM: Modified Sony ICF 2010 barefoot


--- On Fri, 1/9/09, Rick Kunath <k9ao@xxxxxxxxxxx> wrote:

> From: Rick Kunath <k9ao@xxxxxxxxxxx>
> Subject: Re: [IRCA] 4 Foot Box Loop Plans
> To: "Mailing list for the International Radio Club of America" <irca@xxxxxxxxxxxxxxxx>
> Date: Friday, January 9, 2009, 3:14 PM
> Nick Hall-Patch wrote:
> 
> > The NRC altazimuth loop design was intended among
> other things to act
> > as a direction finder, and to optimize nulls, so the
> construction
> > plans are very specific, so as to not introduce
> "vertical effect"
> > from imbalances in the winding, or instability of the
> frame.
> 
> Yes, quite right. But I have found over the years that the
> improved loop balance also improves the Q, and makes sure
> the null depth is all it should be. Out of whack loops I
> have made, often just won't null as deeply as a properly
> balanced loop.
> 
> As far as balancing one up during the building stage, it
> really isn't much harder.
> 
> There are just a few design steps that make all the
> difference.
> 
> I don't use a passive secondary, coupling via the
> primary and a balanced hi impedance preamp, on my last loop.
> 
> I did have a larger loop, larger than the 4-foot diagonal
> measurement, but the smaller loop seemed to have deeper
> nulls, at least inside.
> 
> Rick Kunath
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