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Re: [TowerTalk] K9AY loops-- phased

Subject: Re: [TowerTalk] K9AY loops-- phased
From: Pete Smith <>
Date: Wed, 20 Dec 2006 17:14:54 -0500
List-post: <>
Interesting discussion, Jerry - I wish Tom would chime in.

Another consideration I have been wondering about - there is a graph in ON4UN's 
book (3d edition, page 11-7) that shows the degree of phase shift versus line 
length in degrees, when the phasing line is not terminated in its 
characteristic impedance.  I suspect that many of us, particularly when seeking 
a compromise terminating resistor on a EWE, K9AY etc. aren't THAT careful about 
matching.  This is one of the reasons I was attracted to 180-degree phasing - 
it appears to be unaffected by mismatches, according to ON4UN.

73, Pete N4ZR

At 04:42 PM 12/20/2006, K4SAV wrote:
>A couple of words about RDF (Receiving Directivity Factor) and DMF 
>(Directivity Merit Figure). Both of these may be used as a kind of 
>figure of merit for receiving antenna performance, but neither of these 
>fully characterize everything that is important in determining 
>signal-to-noise ratio for a receiving antenna. A degree of judgment 
>needs to be applied in addition to looking at the number values.
>RDF was originated by W8JI and it is calculated by measuring the forward 
>gain in the "desired" direction minus (in dBi)the total average gain of 
>the antenna.  This is easy to determine because EZNEC will calculate 
>both of these. It's generally a good parameter, but there are a few 
>The first problem is, what is the "desired" direction. Most experienced 
>DX'ers will have a good idea as to what is needed, but the inexperienced 
>ham won't, and the desired direction may be different for different 
>applications. But maybe that's OK on an individual basis because 
>conditions may be different for different people or for different 
>applications.  For example one person may choose 25 degrees elevation, 
>and another person may choose 15 degrees elevation as the desired angle 
>and the direction to be in-line with the lobe. I saw a write-up on one 
>guy's website where he used the desired direction as whatever the 
>elevation angle was for peak gain. That made a low dipole look really 
>good. The point is that numbers generated by different people are going 
>to be different for the same antenna.
>The second problem is that the parameter makes no distinction for lobe 
>shape. In other words, you can squish the forward lobe into any shape 
>you desire as long as you don't change the "gain in the desired 
>direction" and overall average gain (just like a balloon) and the RDF 
>number won't change. The shape however will change the S/N ratio.
>The third problem is that a lot of the response in the forward lobe can 
>be moved to the rear (just like the balloon analogy again).  If the 
>"gain in the desired direction" and average gain are not changed, the 
>RDF number won't change.  Front-to-back ratio MAY be more important than 
>a wider front lobe to some people.
>The point is that the signal-to-noise ratio of the antenna may change 
>significantly and the RDF number remain the same.
>ON4UN recognized some of these short-comings in the RDF parameter, and 
>developed his own parameter, DMF. DMF is the gain in the desired 
>direction minus (in dBi) the average gain in the rear half hemisphere. 
>This is a little different from RDF, but it has some of the same 
>problems. We still have this "desired" direction, so it has the same 
>problems as listed above which may make the number different for 
>different applications. The DMF does give a lot of weight to 
>front-to-back ratio, and so precludes the case of "squishing" some of 
>the forward lobe into the reverse direction without the number changing. 
>It doesn't help the problem of squishing the front lobe into various 
>shapes however. In other words, the front lobe could be horizontally 
>very wide and vertically very narrow, or you could make it very narrow 
>horizontally and very wide vertically.  Both would have the same DMF 
>(and RDF). Clearly the lobe with narrow vertical response would be much 
>more desirable.
>When I first looked at these two parameters and saw the problems, I 
>started developing my own method of measurement, however I never 
>finished it. With a little expertise in recognizing what is important in 
>terms of the shapes of the response curves, you should be able to 
>determine which is best. This however doesn't give you a number, and so 
>comparison between a large number of antennas becomes difficult.  I wish 
>I had finished my method of measurement now, because it would be nice to 
>have something that provided better characterization.
>Another item of importance but not necessarily a large player in 
>determining the S/N is the location of the nulls. These may be important 
>for rejection of QRM from certain directions. That may give more weight 
>to obtaining a good front-to-back or a null at 90 degrees, depending on 
>where you are located and what QRM you would like to reject.
>Jerry, K4SAV
>Terry Conboy wrote:
>> I've followed with interest the discussion about phased arrays of 
>> K9AYs vs. 4 squares, such as the DX Engineering receiving array.  I 
>> decided to model a few variations, and they back up K4SAV's & NI1N's 
>> comments pretty well.  As the basis for performance comparison, I used 
>> the RDF (receiving directivity factor) employed by W8JI.  Here are the 
>> results:
>> Antenna         RDF, dB
>> ========================
>> Whip                    4.7
>> K9AY                    7.3
>> EWE                     7.4
>> 4Sq Whips 90*   10.1
>> 4Sq K9AY 90*    10.2
>> 4Sq EWE 90*     10.2
>> 4Sq Whips 120*  11.6
>> 4Sq K9AY 120*   11.4
>> 4Sq EWE 120*    11.4
>> 1 wl Echelon-Bev        11.5
>> 1.5 wl Beverage 11.6
>> [The 4 squares all use 1/4 wl spacing.  The 120 degree phasing system 
>> is very close to what results from using the crossfire phasing scheme 
>> recommended by W8JI and DX Engineering at that spacing.  The crossfire 
>> system is broadband and can be used over several bands, and the 
>> current phases will vary accordingly.]
>> The bottom line is that a single K9AY or EWE (which are essentially 
>> equivalent if properly installed) is a better receiving antenna than a 
>> single whip vertical, but using them in arrays may be much more 
>> complex than required for good low noise receiving performance.  The 
>> only notable improvement for the arrays of EWEs or K9AYs is a 
>> reduction in the off-axis back lobes, which could be useful for 
>> attenuation of some low angle QRM.  On the other hand, as K4SAV 
>> describes, the array of verticals has a null at zenith, which could 
>> help attenuate lightning static and NVIS QRM.
>> It's also interesting that all of the 4 Square arrays are very similar 
>> in performance to a 1.5 wavelength Beverage or an echelon of 1 
>> wavelength Beverages (staggered by 0.186 wl) with 135 degree phasing 
>> (although the back- and side-lobe structure is different.)
>> Incidentally, models of the DX Engineering array actually show 
>> slightly better RDF (a few tenths of a dB) at closer spacings than 1/4 
>> wl (with appropriate phasing).  I suspect the arrays of EWEs and K9AYs 
>> would be similar.
>> 73, Terry N6RY
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