Re: [IRCA] 4 Foot Box Loop Plans

[Nick Hall-Patch <nhp@xxxxxxxx>]

At 20:14 1/9/2009, Rick K. wrote:


>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.



>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.
>


Good points, Rick.     I have found however that the balancing is most useful for good quality direction finding.  The nulls benefited from tilting, at least for more local signals.   But even with the balanced loop, I sometimes found that introducing a bit of signal from a random wire antenna via a split stator variable capacitor would help even more, using the same principle as the phasing system described recently by Craig Healy.  

Oddly one of my best nulls ever using a loop was on my local on 900 kHz, and that was a tiltable 15" ferrite rod antenna with an unbalanced amplifier, so I don't think that balance in the loop design can always give the best nulls possible; a bit of phasing may still be needed.  In the case of the ferrite rod, I speculate the unbalance was in the "right direction" for an excellent null on that particular station.

Re balanced amplifiers, even Jim Hagan's lower gain FET balanced amplifier crumpled under the onslaught of my locals, so have been using a balanced pickup winding with transformer matching to keep the Q  of the main winding high.

Your final point about smaller loops having better nulls is very pertinent in my experience.  I suspect that there is less vertical effect in smaller designs, and that they are easier to balance.

One point neither of us has mentioned is that indoor loops are likely to pick up a ton of electrical noise from house wiring, computers etc. (not as big a problem in the early days of the NRC loop), and is one reason why so many DXers have migrated back to outdoor antennas  of some kind.

best wishes,

Nick






*****************************
Nick Hall-Patch
Victoria, BC
Canada 

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