SWR meter

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cpedw
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SWR meter

Postby cpedw » Wed Jul 05, 2017 5:46 pm

Having suffered from slowly failing VHF aerials several (at least 2) times, still receiving OK and not aware that I'm unable to transmit more than a 100 yards, I decided to investigate SWR meters.

I found this on the web and decided to give it a try. Mostly very cheap components; the meters were the costly items.

It seems to work on my brand new VHF aerial, reporting SWR of 1.1. And with no antenna connected, it gave the infinity answer. Now I'm a bit outside my comfort zone working with radios but I think this result is probably optimistic. But I reckon that when the aerial starts to fail, this meter will show a change and that will do for me.

I'd be interested to hear comments from radio experts whether this really could be a useful tool to check on the aerial from time to time.

N.B. Very important to turn the transmitter to 1 watt when using the meter. It can't cope with 25 watts!

Derek

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sahona
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Re: SWR meter

Postby sahona » Sun Jul 09, 2017 11:51 am

I always carry my old one from the CB days on the boat. It only cost a few quid and has been diagnosing aerial/cable problems since the early '70s.
I'm surprised you get aerial probelms as opposed to cable corrosion or water ingress.
You'll be popular once you let it be known you can find problems! Another way to identify there is a problem is to note the current the radio draws when you press PTT. It should be about 5 amps at 25 watts. If it's less, it indicates the radio is sensing reflected power and shutting down to protect it's power transistors. Every boat should have an ammeter on the panel!
People will tell you a CB meter is no use at marine frequencies, that's gonads as the whole concept is purely a ratio between output and reflected power.
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bonny
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Re: SWR meter

Postby bonny » Sun Dec 30, 2018 11:28 pm

I too have an old one from CB radio days. Spec'd up to 144MHz (the 2metre amature radio band) but works quite well at 170MHz marine band.
It not only measures the SWR (Standing Wave Ratio) which checks your aerial lead and aerial are ok but also allows you to check the power output of the radio (use a 50 ohm dummy load).

I did modify mine a bit some years ago to replace the diodes with higher frequency ones and shorten some of the stray lead lengths of some components but it made no difference to readings obtained in the marine band.
These SWR meters can be found quite cheaply on eBay, just make sure it covers upto 144MHz (2 metre band) and it should be fine for marine.
I've used it a number of times to check things are ok and it lives on the boat.

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mm5aho
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Re: SWR meter

Postby mm5aho » Tue Jan 08, 2019 10:27 am

I have one too, and can lend it to especially deserving souls.
Geoff.
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DaveS
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Re: SWR meter

Postby DaveS » Tue Jan 08, 2019 6:16 pm

mm5aho wrote:I have one too, and can lend it to especially deserving souls.


Likewise.
Image

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Aja
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Re: SWR meter

Postby Aja » Thu Jan 24, 2019 8:50 pm

I replaced all the cabling and fitted a Metz antenna last year. It's odd when listening to people's voices coming out the speaker when for many years it was little more than silence.

I still wouldn't know, however if it was RX or TX correctly.

Donald


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