[RFI] Link-coupled loop - more.

[Kenneth G. Gordon]

OK. My son, Brendan KB7QEU and I went out after lunch and took 8 more 
bearings with one of Tom Thompson's loops which I had constructed over 
the past few days. 

Tom's loop tunes VERY sharply. I intend to add a bandswitch, a large scale, 
and a vernier dial to it to make it both easier to peak and easier to take down 
a data point.

We carefully plotted the bearings we took on a map of our area of the city.

I connected the loop to the FT-890 in AM mode (BW 6 KHz), tuned to 3573.5 
KHz where "my" noise peaks, and used the FT-890's "S" meter to take 
readings.

First of all, the nulls are not quite as sharp, nor as deep, as those I get with a 
shielded loop, but they suffice. (The shielded loop I was using would 
commonly show a difference from null to peak of over 30 db, while the 
unshielded loop most often provides a difference of only about 10 db).

The results we plotted are somewhat confusing to me as three of the 
bearings did not result in anything common to the other five.

4 of the bearings definitely converge on an area that appears to be around 
an area of about 1 square block which is 4 blocks east of us.

A 5th is close, but outside the convergence zone of the other 4.

Signal strengths became greater as we got up on a hill to the east of my 
station which is also nearer to that 1 block area than some other bearings.

Those three bearings that gave confusing results were the weakest ones, 
and the differences between the null and a peak were only about 1 "S" unit.

However, one odd thing is that two of those three bearings, if I take a 90 
degree normal bearing to those, both show up in the same area as the 4 
"good" bearings. One, in fact, is exactly coincident at its end with two of the 
other "good" bearings.

I don't know how to read those odd ones, but I am not in the habit of 
throwing out data points just because they don't "fit" either. So I don't know 
what to do about them right now.

I suppose I should drive over to that spot 4 blocks east of us and take a look 
around, then take some more bearings.

Probably tomorrow...

Ken W7EKB.