[KLQRP] Terminated folded dipole

[Gary Oneil]

Hi Sir John;

        We sure have been missing you and young Sir Geoff at the 
QRPigOut's. Keep in mind that next month Sir Joe (WA4GIR) and his Lady Liz 
(KO4CK) are hosting the KnightLites at their home on either 9/16 or 9/23 
the third Saturday precedes the third Thursday next month, so we need them 
to weigh in on this and make sure we have the date accurate. Either way... 
This is a weekend affair, and promises to be great fun for all. I hope you 
and Geoff can make it.

        I'm assuming that you're considering the terminated folded dipole 
for receiving purposes only correct? If not, keep in mind that resistors 
convert electricity to heat.... the net being that your ERP is reduced 
proportionally. It's wise to be skeptical about any transmitting claims of 
such antennas. Resistive elements are legitimately used in antenna 
designs, the application being toward pattern alteration, also called 
element tapering. This is most often seen in multi-element arrays where 
sidelobe suppression is important. They too are lossy, but in a controlled 
manner, and the benefit of sidelobe and/or backlobe suppression is valued 
over antenna efficiency. Boresight (mainlobe) gain while somewhat less 
than maximum, is still quite achievable and significant by the property of 
pattern multiplication resulting from the use of many elements in the 
array. 

        I have no "application" experience with terminated folded dipoles, 
and Sirs Todd and Alan may have a more authoritative perspective, but my 
intuitive reactions to these designs are 1) find a good analytical 
reference, or exploit your own initiative to pursue an independent 
analysis. These designs appear to be victims of  mythology, and perhaps 
deserving of a thorough onion peeling as I've done with the J-pole. :-) 2) 
As half-wave dipoles, they will be no more directive than conventional 
dipoles, and with resistors which will dissipate some amount of power, are 
of lower efficiency. 3) If there is any merit to their design, It's likely 
related to how it behaves in the presence of orthogonal traveling waves; 
presumably suppression of these via lossy termination and field 
cancellation.

        Given that the above "intuitive" assessment proves to have any 
basis in fact, the merits of such designs would be a small compromise in 
antenna efficiency with an overall improvement in noise suppression from a 
fixed and specific direction. This direction being precisely orthogonal to 
the desired direction of communication. It's noise cancelling properties 
might be compared to the beverage antenna, but with the objective of 
traveling wave suppression rather than enhancement. So if you have an 
annoying noise generator at right angles to the direction in which you 
wish to communicate, this may be something worth pursuing, but for receive 
only applications. I would use caution when hearing unsubstantiated claims 
of extraordinary performance, DX achievements, etc. The next time you hook 
up with Sir Alan, ask him to tell you his story about a very expensive 
dipole sold to our military on it's merit of having low VSWR across the 
entire HF spectrum. 

Regards;

Gary E. O'Neil
Applications Engineering
PowerPC Enablement and  Applications
IBM Microelectronics 
3039 Cornwallis Road, 062/E112
Research Triangle Park, NC  27709
(919)-543-5750    T/L 441-5750


Resolution of disagreement ALWAYS leads to better understanding... 
assuming all parties survive the conflict. 



"John McKee" <JOHNM at rfmd.com> 
Sent by: klqrp-bounces at knightlites.org
08/17/2006 08:40 AM

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Subject
[KLQRP] Terminated folded dipole






Anyone have experience with a terminated folded dipole, preferably the 3 
wire version.  I'm looking for some real world data.  Found lots of 
articles on the web but very little measured or simulated data.  L.B. 
Cebik has a comparison of several versions on his website, but it's all 
simulated.  73, John WB4OFT_______________________________________________
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