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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #11  
Old 07-02-2008
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SEMIJim will become famous soon enough SEMIJim will become famous soon enough
Quote:
Originally Posted by jdair101 View Post
Ok== today I picked up an emergency antenna and guess what-- I can both receive and transmit.
That narrows it down a bit .

Quote:
Originally Posted by jdair101 View Post
Before I made the purchace I checked the wiring from the radio to the base of the mast and it was ok.
Define "checked the wiring."

Quote:
Originally Posted by jdair101 View Post
Next I checked for resistance at the base of the mast and it was open.
Did you read that article to which I pointed you earlier? Under "Testing":
Quote:
Simple Test. It may be possible to perform a simple test on the antenna after you have installed the connector by measuring the DC resistance between the connector's center pin and outer shield (obvously, the radio must be disconnected from the antenna to do this). Oddly enough, you may measure either an open (high resistance) or a short (low resistance). This characteristic is dependant on the antenna's design,...
Quote:
Originally Posted by jdair101 View Post
So I guess up the mast I go.
Indeed. But you'd be well-served by reading that article, first, so you have a better idea of what you're doing.

Simple test of coax:
  1. Disconnect from radio and antenna
  2. Check at either end for open between center-conductor and shield
  3. Short center-conductor to shield at either end (doing this well is harder than it seems)
  4. Check for near-zero ohms resistance at other end (getting the meter probes electrically firmly on both center-conductor and shield is harder than it looks)
You can check the antenna for it's characteristic DC resistance, assuming it's not (already) broken, by putting the meter across the center-conductor and shield before connecting the coax, too. It will measure either open, or extremely close to zero. Knowing which of those it should be is important, of course.

But: DC resistance tests on antenna systems are a crude check, at best. Assuming they check out, DC-wise, you really need to put an SWR bridge on the system, as well.

Then, if/when that all checks out: You need to test it in real life with some test communications.

Good Luck.

Jim

Last edited by SEMIJim; 07-02-2008 at 08:01 AM.
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