[Boatanchors] Off Topic: Question about Mosley beams

[Gary Schafer]

Hi Mac,

I had a TA 33?? Up several years ago. It was broad banded just as they advertised but it always had a double dip in the SWR across the band. I removed the shorting strap and got a nice single SWR dip but the bandwidth was narrower. 
Like you, I could never figure out why they would ground one side of the driven element and unbalance it. Apparently that is how they got the increased bandwidth.
I asked the factory about it and of course they said they never heard of the problem.

The coil of coax makes a fair balun if it is wound flat, like on a 4" diameter pipe. I did that but did not leave the pipe in it. I just taped it to maintain the shape. Used it that way for several years with the ground strap removed.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of D C _Mac_ Macdonald
> Sent: Saturday, December 14, 2019 6:44 PM
> To: boatanchors at mailman.qth.net
> Subject: [Boatanchors] Off Topic: Question about Mosley beams
> 
> I know that Mosley promotes a "direct" feed from split out coax for
> their direct feed dipole radiator sections.  I presume it is because
> they actually ground the non-fed side to the tower structure and perhaps
> consider that makes it an unbalanced feed.  Mosley states that no balun
> is necessary.  A coil of coax IS recommended as a choke.
> 
> Is it possible or even likely that the 2.5 to 3 inch "Y" of the split
> coax is performing some impedance matching for the antenna?
> 
> However, I wonder if using a good quality 1:1 balun while ungrounding
> the "cold" side of the driven element would be a good thing, bad thing,
> or not matter.  I suspect weather-proofing would be easier using a
> sealed balun.
> 
> I admit that this is something I have wondered about for well over 50
> years and since I have a new Mosley PRO-57-B-40 on order, now is the
> time to seek some guidance !
> 
> 73 de Mac, K2GKK/5​
> Since 30 Nov 1953​
> Oklahoma City, OK​
> USAF, Retired ('61-'81)​
> FAA, Retired ('94-'10)​
> 
> 
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