Topband: dipole height

K4SAV RadioIR at charter.net
Wed Oct 31 10:38:23 EDT 2012


James Wolf wrote:
> In general, this is the case, but it is not always true.  Consider that you
> can have an antenna with a high RDF number, but at the same time has a
> pattern where rear lobe positions favor the optimum elevation angles for
> arriving propagated atmospheric noise.  If you look at some of the various
> Low Band receive antennas and vary their parameters around, you can end up
> with high RDF number with significant lobes off the back that are only 10 dB
> down from the main signal.  The pattern is always a compromise and a good
> RDF number is a great tool to have in the box, but it is not the only
> consideration.  
>
> Jim, KR9U
>
>   

That's very true.  Consider the K9AY.  The RDF is about 7.7.  Compare 
that to a 1 wavelength Beverage which is about 7.9 dB.  The K9AY has a 
deep null in the 180 degree direction at the right elevation angle, but 
45 degrees off that rear direction the signal is down only 10 dB.  The 
RDF number is a W8JI creation and serves its purpose, while the DMF is 
an ON4UN creation and also has merit, but neither of these completely 
encompasses all the things you may need to know about a receiving 
antenna for your location.  You have to use some common sense in 
junction with these numbers.

Jerry, K4SAV




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