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 <[email protected]> FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15' AM: Modified Sony ICF 2010 barefoot --- On Fri, 1/9/09, Rick Kunath <[email protected]> wrote: > From: Rick Kunath <[email protected]> > Subject: Re: [IRCA] 4 Foot Box Loop Plans > To: "Mailing list for the International Radio Club of America" > <[email protected]> > 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 > _______________________________________________ > IRCA mailing list > [email protected] > http://montreal.kotalampi.com/mailman/listinfo/irca > > Opinions expressed in messages on this mailing list are > those of the original contributors and do not necessarily > reflect the opinion of the IRCA, its editors, publishing > staff, or officers > > For more information: http://www.ircaonline.org > > To Post a message: [email protected] _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
