Hi JW,
The feed line on the loop was chocked with two common mode chokes. The
null on the loop is quite deep. The orientation not being as precise as
it could be is the reason the null is not as deep as expected. In RFI
tracking I have seen at least a 20-dB null with a single common mode
choke with this loop.
Tom
On 6/13/2017 1:54 PM, JW wrote:
Interesting experiment and thank you for sharing.
1) I would note that the loop's null would be deeper if a shielded (or
choked) pickup loop were used. I could not determine from pictures the
exact construction, but have seen responses from unshielded loops
before (currents on feedlines become a factor.).
2) I worked out an E-field xmit antenna a few years back and noted
response of the ends, with unexpected nulls off the *broadside*. A
very quick backyard test of the pattern here; listen to the audible
null at broadside from the test receiver (ignore all the noisy birds):
(Also recommend playing at half speed)
https://www.youtube.com/watch?v=TxxosnZo0i4
When I first constructed this oddity of nature I noticed that the
usual noise sources nulled off the *broadside*, instead of off the
ends as the usual 1/2 wave dipole characteristically exhibits
de Jim WB5WPA
PS fo = 7 MHz in above test
------------------------------------------------------------------------
*From:* Tom Thompson <w0ivj@tomthompson.com>
*To:* Rfi List <rfi@contesting.com>
*Sent:* Tuesday, June 13, 2017 12:49 PM
*Subject:* [RFI] Polarity Tests
Some of you have mentioned in the past about using a tuned loop for
tracking RFI. A question has sometimes arose about the direction of the
null of the loop. Larry Benko, W0QE, and I did some polarity tests
using various orientations of both the transmitting short dipole and a
receiving loop and a receiving short dipole. The results are shown here:
http://tomthompson.com/radio/Antenna_Polarity/Antenna%20Polarity%20Measurements.html
73, Tom W0IVJ
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