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  #1  
Old 03-24-2009
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testing antenna for vhf

My new-old boat has a vhf antenna mounted atop the mast with cable inside the mast. How can I test my antenna and cable before I put up the mast? I have a servicable multimeter and the mast is down. Everything's accessable now. The radio, I was told, no longer works and I don't want to plug the antenna into a new radio and ruin it.
Mike
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Old 03-24-2009
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Testing with a multimeter is of limited benefit. It can tell you if there is a short or no continuity but will not indicate a marginally corroded connection, impedance mismatch, moisture inside the coax braid or high reflected power (SWR).
Start with the multimeter to verify no shorts exist, if in doubt, replace all coax connections which also allows inspection of the coax ends to see if there is moisture entrapped and use an SWR meter to verify everything works properly.
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Old 03-24-2009
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Get a radio that works. Get a handheld VHF. Try transmitting on channel 68 with and without the antenna. TADA! The antenna works, now put it on top of the mast!
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Old 03-24-2009
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Ask around and find out where your local HAM radio club is. Find their web site. Call up the president or any member and say to them:

"I have a problem I am not sure if you can help me with. I have a VHF radio on my boat. I am told it is in the 2 metre range. Do you know anyone who might have a 2 m SWR meter and might be able to take a few minutes and tell me if the antenna is tuned right? I would be happy to buy them a coffee or a beer after."

Rational
  1. Everyone likes to solve someone else's problem
  2. HAM radio guys like to share their expertise
  3. HAM radio guys usually have SWR meters
    many HAM radio guys like coffee or beer
  4. And lots of them are retired and have lots of time on their hands

I know - I am a HAM radio guy, retired, with time on my hands, and know which HAM guy I could borrow a 2 M SWR meter from.



Information:
  • The 2 metre band is the band that VHF is in
  • The SWR meter or VSWR (voltage standing wave ratio) meter measures the standing wave ratio in a transmission line. This is an item of radio equipment used to check the quality of the match between the antenna and the transmission line.

Rik
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Old 03-24-2009
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IIRC, transmitting on a VHF without an antenna attached may fry the radio. Not a good idea.
Quote:
Originally Posted by tager View Post
Get a radio that works. Get a handheld VHF. Try transmitting on channel 68 with and without the antenna. TADA! The antenna works, now put it on top of the mast!
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Old 03-24-2009
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Sailingdog: that's why I don't want to plug a new radio into an untested antenna. For all I know, that's why the existing radio is kaput. I have fried a CB by keying the mike without an antenna connected.
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Old 03-25-2009
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If it is at all suspect, this would be a great time to run a new cable and replace the antenna. Very suprised SD did not say this
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I'd have to agree.. if you've got any doubts, it is far better to run new cable than worry about it... A new Metz 3 dB 3' whip is only about $40, and they're bulletproof.
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a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

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Old 03-25-2009
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when in doubt, throw it out. since mast is down, its better to fix what need be done. if the cable is several years old might as well change it or you may have to change it later (regret...regret).
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hummm not even a total replacement will guarantee your antena is working (soldering, connectors, splices, running clables, etc). Your VHF will not be damaged by a 1 second call to a hadheld for a quick check, your multimeter will grant "phisycal shorts", and only a SWR meter could tell you about performance also. Indeed, you should not take my advices as granted, this is just what I've done myself on several occasions I faced this same problem. If you go "by the book", taking strictly all advices, you'll might end up concluding your antana may cause cancer ....
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