Topband: RDF in the real-world

donovanf at donovanf at
Fri Mar 4 13:21:26 EST 2016

Hi Lee, 

I recently had exactly the same experience with my 160 meter W8JI 
passive 8-circle array. About six weeks ago intense broadband 
white noise appeared at my QTH arriving at about 325 degrees 
azimuth, between the 315 and 0 degree peaks of two main lobes 
of my 8-circle array. 

I was able to very accurately determine the azimuth that the signal 
must have been arriving from by plotting the difference in signal 
strength on the EZNEC V6+ pattern of the two main lobes. This is 
exactly the same method used by state of the art HF direction finding 
arrays that use a huge database of the full hemisphere vs. frequency 
response of their direction finding antenna to determine the azimuth 
and elevation angle that a signal must have arrived at to produce the 
resulting voltages in the antenna 

The actual location of the source was only 2 degrees off from my 
calculation, a malfunctioning licensed 10 watt Traveler Information 
Service transmitter on 1700 kHz two miles from my QTH operated 
by my local county government. Excellent relationships between 
our local ham community and the county resulted in the transmitter 
be turned off within a few hours of reporting the problem to the 
responsible person. 


----- Original Message -----

From: "Lee STRAHAN" <k7tjr at> 
To: "JC" <n4is at>, "160" <topband at> 
Sent: Friday, March 4, 2016 6:00:23 PM 
Subject: Re: Topband: RDF in the real-world 

Hello JC and others, 
I must take a little issue on being able to measure the vertical arrays. While it may be true that it is hard to measure, you can indeed see the pattern quite well by looking at different stations and switching around the compass. It does not take long before you can observe the pattern and can tell that there may be something wrong with it. In my case there are 2 lobes on the side of the patterns of my best antennas and you can certainly see the results for even slightly skewed signals because of them. 
I recall an instance a few years ago where W0FLS was able to DF a long standing carrier on 160 within 1 or 2 degrees using his 8 circle and his observations about pattern. 
So it is like your RDF and signal to noise description, it is not easily measurable but observable. Yes, Directivity rules. 
Sorry I missed your webinar due to other commitments. I will be able to view it when it is archived. 
Lee K7TJR 

-----Original Message----- 
From: Topband [mailto:topband-bounces at] On Behalf Of JC 
Sent: Friday, March 04, 2016 9:31 AM 
To: k1fz at; 'Carl Luetzelschwab' <carlluetzelschwab at>; topband at 
Subject: Re: Topband: RDF in the real-world 

Hi Carl 

Yes, the concept is assuming equal density noise spread uniform. However there air point everybody wants to hide. Vertical polarized antennas based on phasing elements does change directivity and does have interaction with others vertical elements. It is hard to measure it because you cannot turn the antenna for different directions to measure it. 

The Bog is a travel wave antenna, and it is based on the difference in velocity on the ground and on the wire, it does not interact or deteriorate with other vertical structures like the flags. The SAL antenna is really a K9AY very complicated but same directivity and RDF, the TX antenna does deteriorate the pattern and you can’t see the same reduction in signal to noise ratio because the REAL RDF is no longer the same as the CALCULATED RDF. The BoG performance is more predictable, like the beverages and the real RDF is close to calculated RDF. 

Like you see in the diagram when I remove the detuning skirt from my TX antenna, with that tiny yellow jumper grounding the skirt, the radiation patter of my excellent VWF become useless without detuning the TX antenna. 

The Webnair is limited to one hours and there are interesting aspects of each antenna that deserved more time to elaborate, maybe next time with dedicate one hour for each type of antenna. 

The idea was to quantity what directivity can do for you in practical DXing. 


-----Original Message----- 
From: Topband [mailto:topband-bounces at] On Behalf Of K1FZ-Bruce 
Sent: Friday, March 04, 2016 10:02 AM 
To: Carl Luetzelschwab <carlluetzelschwab at>; topband at 
Subject: Topband: RDF in the real-world 

I agree. There are times, especially in disturbed condx, when my BOG antennas are "head and shoulders" better than my other antennas. 


I can't vouch for JC's numbers (his numbers may be QTH specific), but the concept is believable since the theoretical assumption of isotropic noise falls apart in the real-world. My BOG *at times* gives much more of an SNR improvement than the SAL-20 (using measurements on a calibrated S-meter) in spite of the small difference in RDF between the BOG and SAL-20. 

Carl K9LA 
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