[Lowfer] Loop Practice ?

[Bill Ashlock]

> The null when using all 14 turns was about 21 dB, but it dropped to 17 > dB when only 7 turns were used.
 
Interesting measurement, John! Here we are back at the need for a portable SVM so you can adjust as you watch :)  One can even rotate the plane of the loop in the axis pointing toward the signal source to achieve and even deeper null - sometimes as low as 40 db if the loop is well balanced. 
 
Oh, BTW, your comments bring up another point: Why is it that few use rotators, in fact cheep ones, to rotate their loops? In my case I think I drifted away from using rotators even though I have accumulated many of then through the years, because of the overall loss in performance... mostly S/N. Now I realize that the rotator cable must have been the culprit - bringing noise from the shack ground system out to the antenna site... same as using a lead-in without a coupling/isolation transformer in the shack. Suppose winding a sufficient number of turns of the rotator cable on a high-perm core would take care of this problem.
 
Bill
 
 > Date: Wed, 30 Jul 2008 19:27:32 -0400> From: w1tag at w1tag.com> To: lowfer at mailman.qth.net> Subject: Re: [Lowfer] Loop Practice ?> > Peter, Bill,> > OK, here are the results. I used an aero beacon about 5 miles away on > 417 kHz, and the readings were taken about 1.5 hours before sunset, so > the signal was stable. The nearby big loop was shorted and grounded, so > there would be no unusual tuning effects.> > The null when using all 14 turns was about 21 dB, but it dropped to 17 > dB when only 7 turns were used. So...on the face of it, Bill may have a > point. The presence of the grounded conductor for the 480' perimeter > xmit loop being only 10 feet away sets up some possibilities for > electrostatic coupling. The nulls seemed symmetrical, when the loop was > rotated 180 degrees, to the best of my ability to measure. Since I don't > have a rotator on the thing, this required some back and forth trips > from the house, and the use of wireless headphones to hear the null.> > The balance of the loop otherwise should be pretty good, as it is series > tuned into a winding on a toroid.> > JA> > John Andrews wrote:> > Peter, Bill,> > > > I have a 7-turn tap on my 14-turn loop (6' square), and have used it > > before with no strange results. But Bill makes a very good point. If the > > time and weather permit tonight, I'll try to measure the depth of a null > > both ways. Will probably have to do it with an aero beacon down in the > > 200-300 kHz range. Stay tuned...> _______________________________________________> >From the Lowfer mailing list> Send messages to: Lowfer at mailman.qth.net> To sub/unsub visit: http://mailman.qth.net/mailman/listinfo/lowfer