[UK-CONTEST] VHF beams

[Alex GM3ZBE]

I've just bought and installed a Moonraker 3ele for 50MHz.  Generally 
the mechanical construction was rather better than I expected,.  I don't 
know about the quality of the aluminium but I live in a very exposed 
location, so time will tell!

The beam is gamma matched but it simply was incapable of matching in the 
50.5 MHz region of the band, it could match perfectly on about 52.5MHz 
but there was no way I could get it down to the appropriate part of the 
band with the specified dimension for the driven element.  The best I 
could do was to get it down to 1.8:1 swr at about 50.5MHz by extending 
the driven element length and fiddling with the the gamma matching 
adjustments.  I spent about 3 days off and on struggling with it!  I 
eventually gave up and made a small matching unit at the shack end of 
the coax.  I am pretty conversant with antennas and playing about with 
matching systems, so I like to think the problems were not lack of 
experience on my part :-)

As a matter of interest I modelled the antenna in EzNec and the gain and 
pattern was in quite close agreement with the Moonraker specs.  I didn't 
try to model the gamma match part as that is quite difficult to do 
meaningfully in a model.    The contact between the driven element and 
the boom was unreliable,  it seemed to rely on the element tubing being 
squashed on to the thread of the element fixing bolt when it was 
compressed.  This wasn't the cause of the basic matching problem though.

I will probably change the matching arrangement later to get round the 
problem, the beam is cheap and relatively well made apart from the 
matching problem.

John Lemay wrote:
> My personal opinion, I wouldn't touch Moonraker. Take a look a M Squared,
> Eagle, Cushcraft, I0JXX.
>
> John G4ZTR
>
> -----Original Message-----
> From: uk-contest-bounces at contesting.com
> [mailto:uk-contest-bounces at contesting.com] On Behalf Of Andy Swiffin
> Sent: 08 May 2009 10:14
> To: uk-contest at contesting.com
> Subject: [UK-CONTEST] VHF beams
>
> Hi
> Sorry to be slightly OT, but  what "does the team think" about Moonraker ZL
> specials for 2M, say the 12ZL versus their 11ele standard yagi?  Do ZL
> specials _really_ work as claimed?
>
> If you wouldn't buy moonraker, what would you buy?
>
> I'm having to re-equip with antennas for 6, 4 and 2 and will be on for the
> contests "real soon now".  (so its not really OT at all :-)
>
> 73
> Andy
> gm8oeg
>
>
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