You will have to argue with the Mosley engineers, not me. That was a direct
quote from:
http://www.mosley-electronics.com/faq.htm
Works fine for me plus a whole bunch of LORAN station ham stations.
K4SB wrote:
> > FEED SYSTEMS - THE SIMPLER, THE BETTER!
> > Despite popular belief, linear radiators, normally employed in 2 and 3
> > element parasitic arrays, have a driving point impedance of close to 52 ohms
> > when open at the center. To feed such a radiator it is only necessary to
> > connect a 52
> > ohm line at this point to achieve the best possible match of line to
> > antenna.
>
> Nope, depending on the spacing of the parasitics, it will range from
> generally 20 to 30 ohms. And optimized, the figure is about 20 ohms.
> You have to have some pretty wide spacing between the Reflector and DE
> to get 50 ohms. And there is certainly nothing unstable about a gamma
> or hairpin match. And if you find this on a trapped antenna, you can
> bet your boots the traps are adding both resistance and reactance to
> the system.
>
> Now, I have 3 long boom 5 element yagis on 20, 15, and 10 on separate
> towers. They all are directly fed through a balun, and they all have
> an impedance of 50 ohms, but, this was a design I developed myself (
> by mistake ) and the first director is so close to the driven element
> you wouldn't believe it. About 18 inches on the 15. None of these
> yagis have a F/B of less than 50 db at resonance. The greatest
> determining factor in the impedance, besides that 1st director, is the
> spacing and length of the 3rd director.
>
> And believe me, the spacing between elements is critical. I have a
> 1000 mm long rule obtained from McMaster Carr, and those placings are
> set to within .5 mm.
>
> Have purchased 1 commercial antenna in almost 50 years, a
> TH11-DX...and don't ask.
> That thing is an absolute killer on 17, but I have severe doubts it
> gets much further than a couple hundred yards away on all the others.
>
> 73
> Ed
--
__________________________________________________________________________
Alan Zack
Amateur Radio Station K7ACZ
Las Vegas, Nevada, USA
Quality Engineer, The Boeing Company, Retired
Aviation Chief Warrant Officer, U.S. Coast Guard, Retired
U.S. Coast Guard, Always Ready, Always There
Every hour, Every day, Around the Clock and Around the World
SEMPER PARATUS
http://www.gocoastguard.com/
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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