SWR meter

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cpedw
Old Salt
Posts: 624
Joined: Fri Aug 20, 2004 11:38 am
Boat Type: Nordship 35DS
Location: Oban

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
Admiral of the White
Posts: 1958
Joined: Thu Jan 03, 2008 8:17 pm
Boat Type: Marcon Claymore
Location: Clyde

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.
http://trooncruisingclub.org/ 20' - 30' Berths available, Clyde.
Cruising, racing, maintenance facilities. Go take a look, you know you want to.


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