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Old 03-04-2010, 06:22   #1
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VHF Aerial

Hi Guys

my VHF is driving me nuts how do i check if the antenia is working properly?

i live quite a distance from the sea and my boat is in my back yard.Can i do some sort of a resistance check? i also have a swr meter if thats any use.
My boat is a trailer sailor so i have to cut the VHF cable and fita deck plug.I have used the manufacturers reccomended VHF deck plug

hellp
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Old 03-04-2010, 06:48   #2
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An SWR meter should do it, if it is rated for VHF frequencies. You won't really know unless you can make a radio check contact with someone a good ways off.
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Old 03-04-2010, 10:06   #3
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Best place to put the SWR meter is at the antenna. My radio was putting 22 watts out with an SWR of better than 2:1 measured at the radio. When I checked at the mast base connection there was 0 watts. The coax had corroded, but still had an impedence close to 50 ohms so the radio was happy, I was just warming the settee instead putting out a signal.

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Old 03-04-2010, 10:39   #4
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The SWR of 2:1 was also an indication that something was seriously wrong. You must check it on the first and last channel plus ch. 16. The average should be 1.5:1 max.
A dummy load really helps too as it allows you to compare readings but remember that a good dummy load will always read very good like 1.1:1 on every frequency; something an antenna can't match.

cheers,
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Old 03-04-2010, 12:16   #5
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I am 20 miles from the sea with no mountains in the way so i would assume that i would pick something up,(same landscape as holland)

I have found an antenai for $40.00 i will give that a try

my SWR meter is for a cb radio,so im not even sure if that works on marine frequency,when i transmit the needle flys to the end of the scale
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Old 03-04-2010, 13:31   #6
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The SWR meter has a label stating the usable frequency range. You want one to go up to 200 MHz at least (many CB versions are okay).

For power you need a way to calibrate it on the used frequency. Many cheap CB meters can't do that so the value shown on the meter is not usable to determine power level... but you can use it to find differences along the line (cable). Most have a switch to change the range; it should have a usable setting.

Lincolnshire.... yes you should pick up transmissions 20 miles away but there must be those transmissions to start with... I haven't sailed in the UK for 10 years but it was pretty quiet on the VHF then... unlike in the USA.

cheers,
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Old 03-04-2010, 21:26   #7
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Regular VHF is line of sight. It's probably working, but if there isn't anybody using a VHF within line of sight (unlikely if they're not on a boat) you won't get anything. If it's an SSB go to an AM setting and see if you can hear anything. West Marine sells a decent deck plug for both VHF and SSB.
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Old 03-04-2010, 21:47   #8
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Quote:
Originally Posted by s/v Jedi View Post
The SWR of 2:1 was also an indication that something was seriously wrong. You must check it on the first and last channel plus ch. 16. The average should be 1.5:1 max.
A dummy load really helps too as it allows you to compare readings but remember that a good dummy load will always read very good like 1.1:1 on every frequency; something an antenna can't match.

cheers,
Nick.
I said better than 2:1. I knew there was something wrong due to weak reception and no transmission. Too long ago but IIRC it was somewhere between 1.5 and 1.8, which I know is suboptimal, but should have a usable but shorter range signal. What surprised me, the point I was trying to make, was that a completely corroded cable that passed no signal at all to the next section of coax, I eventually found to have infinite resistance on an ohmmeter, had an impedance close enough to 50 ohms that the radio was willing to put out full or near full power with an SWR while not good should have been usable.

John
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Old 04-04-2010, 06:00   #9
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The only way that i think ill get peace of mind,is to go down towards the coast and try it all out.

I bought the Standard horizon unit last year and it first was used last Sept,I used the wrong type of deck plug so it did not work,now im concerned that i could have damaged the unit,i did not use it other than a few attempts at transmitting.
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