[RFI] Link-coupled loop - more.

tlthompson tlthompson at qwest.net
Wed Apr 2 20:41:42 EDT 2014


Charlie,

What I do is null the signal with the loop.  Since the RFI signals all 
seem to be vertically polarized, You are looking through the loop in the 
direction of the nulled signal.  I site a distant object through the 
loop and then get a compass bearing from the object. That being said, 
rather than take careful bearings, I find it more productive to walk in 
the direction of the signal while alternatively looking for a peak and a 
null until the signal is very strong.  At that point I can always 
identify the house where the RFI is emanating.

Tom   W0IVJ

On 4/1/2014 5:26 PM, n0tt1 at juno.com wrote:
>> We carefully plotted the bearings we took on a map of our area of
>> the city.
>   
> I've often thought about attaching, say, a boat or auto compass to
> the loop support....might make the plotting easier.
>   
> Does anyone know of a "good" model of compass that would
> work for that purpose?
>   
> 73,
> Charlie, N0TT
>   
> On Tue, 01 Apr 2014 15:24:23 -0700 "Kenneth G. Gordon"
> <kgordon2006 at frontier.com> writes:
>> 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.
>> _______________________________________________
>> RFI mailing list
>> RFI at contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>>
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
>



More information about the RFI mailing list