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Old 11-05-2010, 14:39   #1
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Antenna or SWR Bad

I just replaced the antenna wire in my mast for a new line. This is the first year that I will use this boat and the old VHF was an original by the looks of it (1972) I put in a new dcs radio so thought the cable should go. My problem is when I hook up the SWR meter to test I do not get any movement on the needle. I am wondering if this is a sign that the swr is bad or if the antenna is no good.

I am trying to figure out if I need to replace the antenna or if the one that came with the boat is still good. It is a shakespear antenna and looks OK, but I would rather figure this out now, while the mast is lying on the ground. The boat goes in the water on Friday so I really would like to get this sorted out.

Oh and yes the swr is one meant for ham radio.
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Old 11-05-2010, 15:45   #2
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Originally Posted by Captin_Kirk View Post
I just replaced the antenna wire in my mast for a new line. This is the first year that I will use this boat and the old VHF was an original by the looks of it (1972) I put in a new dcs radio so thought the cable should go. My problem is when I hook up the SWR meter to test I do not get any movement on the needle. I am wondering if this is a sign that the swr is bad or if the antenna is no good.

I am trying to figure out if I need to replace the antenna or if the one that came with the boat is still good. It is a shakespear antenna and looks OK, but I would rather figure this out now, while the mast is lying on the ground. The boat goes in the water on Friday so I really would like to get this sorted out.

Oh and yes the swr is one meant for ham radio.
Depending on which SWR meter you have and its designed range, it might not yield accurate results at VHF frequencies. However, you'd certainly see some meter movement.

My advice: check all your connections VERY VERY carefully. With the coax disconnected at both ends, see if there's a short between the center conductor and the braid. If not, check the continuity of both the center conductor and the braid, to be sure there's no break. BTW, what coax are you using? RG-8X is acceptable, RG-213 or 214 or LMR400 are much better. But, you've gotta be absolutely sure the PL-259 connectors are installed on the coax correctly.

RE: the antenna, since this is a relatively small expense, I'd install a new one. Get a simple 3db gain marine VHF antenna. The cost is so little, it's not worth fooling around, particularly since your mast is down and you have easy access.

FWIW,

Bill
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Old 11-05-2010, 18:45   #3
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Bill's comments are good but I make one more suggestion. If your SWR meter is indeed fit for 156 MHz does it also have forward power and reflected power readings? If you can not see SWR maybe you can measure the power going out then see how much is coming back. Effectively measuring SWR. You should do this on low power but most VHF's will handle it even in high power if you do not transmit too long.

Cheers

Mark
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Old 11-05-2010, 18:52   #4
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"Oh and yes the swr is one meant for ham radio. "
Most general purpose "ham radio" SWR meters would probably be designed for HF use, maximum of 30MHz frequency. That will also work for CB, but not marine VHF.

For marine VHF (156MHz roughly) you need an SWR meter designed for "two meter" VHF ham radio, nominally 144MHz.

If the antenna and cable are circa 1972, or even 1992, I would expect it is time to replace them if you want max performance.
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Old 12-05-2010, 03:53   #5
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Well this seems like a silly question for me to be asking, but since your mast is on the ground, you are connecting your radio to a battery and putting the swr meter in line with the antenna wire and transmitting on the radio, correct?

Eric
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Old 12-05-2010, 04:48   #6
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Yes, everything is connected. I am going to try the swr on my Ham radio in the truck and see if it works there.
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Old 14-05-2010, 14:56   #7
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If you fabricated the coax cable it's possible that's the culprit. With both ends disconnected, measure the resistance from the center to the shield - should be infinite. Then short the center to the shield at the antenna and measure again - should get 0.

You could ohm the antenna but they generally measure 0 at DC.

You might check that you're getting 12VDC at the radio. Some radios shut down or reduce output power as the voltage decreases.

And check the SWR meter. Chances are it's rated for HF not VHF.
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