[RFI] Polarization Tests

[Tom Thompson]

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 at tomthompson.com>
> *To:* Rfi List <rfi at 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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