Moderated Discussion Areas
ContinuousWave: Small Boat Electrical
|Author||Topic: Antenna Dissection|
posted 07-13-2013 04:53 PM ET (US)
A while back I dissected a failed Shakespeare Galaxy VHF antenna, and I've posted pictures of it at
http://chucktribolet.smugmug.com/BostonWhalerRendezvous/ Antenna-Dissection/ .
Perhaps Jimh can explain what all the pieces inside are.
posted 07-13-2013 05:22 PM ET (US)
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.
posted 07-17-2013 12:27 PM ET (US)
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.
posted 07-17-2013 12:29 PM ET (US)
I forgot to ask how the antenna failed. Physical damage to the antenna or just prolonged use?
posted 07-18-2013 08:59 AM ET (US)
Antenna performance can be affected by the construction of the conductive elements. In general, larger diameter is preferred. Lower resistance is preferred.
posted 07-19-2013 04:14 PM ET (US)
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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