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Author Topic:   Antenna Dissection
Chuck Tribolet posted 07-13-2013 04:53 PM ET (US)   Profile for Chuck Tribolet   Send Email to Chuck Tribolet  
A while back I dissected a failed Shakespeare Galaxy VHF antenna, and I've posted pictures of it at Antenna-Dissection/ .

Perhaps Jimh can explain what all the pieces inside are.


jimh posted 07-13-2013 05:22 PM ET (US)     Profile for jimh  Send Email to jimh     
The upper segment appears to be about 36-inches long or slightly longer. That suggests it is a half-wavelength or perhaps 5/8-th-wavelength, and it is the primary radiating portion. The lowest part looks like it is about 18-inches long. That suggests it is about a quarter-wavelength, and it is probably part of the counterpoise.

In the middle area there looks to be a sleeve capacitor, formed by the capacitance between the outer tube and the inner segment, which is probably made from part of a coaxial transmission line center conductor and dielectric insulator. That appears to be part of a matching network that connects the upper portion to the lower portion. Or it could be a shorted stub. It is hard to tell without being able to see close-up how the various components are connected.

17 bodega posted 07-17-2013 12:27 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Did you buy the same model for replacement Chuck? Did you go with the GAM SS-1? I still haven't made a decision yet on an 8 foot whip or a 3' steel whip. I am also unclear on the gain structure. Most of the shake 8 footers are 6db and the 3 footers are 3db. The GAM states 3db on their website but the retailers tout it as a 6db gain antenna. I'm confused.

Great pictures. it looks a lot like mine when taken apart.


17 bodega posted 07-17-2013 12:29 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
I forgot to ask how the antenna failed. Physical damage to the antenna or just prolonged use?
jimh posted 07-18-2013 08:59 AM ET (US)     Profile for jimh  Send Email to jimh     
Antenna performance can be affected by the construction of the conductive elements. In general, larger diameter is preferred. Lower resistance is preferred.
17 bodega posted 07-19-2013 04:14 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
I just dissected a cheaper "west marine" branded antenna by Shakespeare that was not as nice as that one. It had coax with a much smaller copper core than that Galaxy.

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