VHF aerial SWR

[jimbouy]

I have an SWR meter from my CB days. Can I use this to check the SWR when I install my VHF aerial?? or SWR meters frequency dependent?



<hr width=100% size=1> "It is a pleasure to give advice, humiliating to need it, normal to ignore it"

 

[steve_cronin]

Slightly and since 156 is a long way from 27 it isn't that accurate. I too have a CB SWR meter but I also have a proper VHF one made in the US by Shakespeare Antennas. I have only used them comparitively once, on my last boat and as I remember the CB one gave 1:4 whereas the VHF one gave 1:1.75 (or thereabouts).

I DO lend it out for an RNLI donation!

Steve Cronin

<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[wooslehunter]

SWR meters are frequency dependant but you should find it'll work OK. If it measures power, then don't expect that to be accurate. Since VSWR is a ratio: you set the meter to full scale forward & then measure the reverse power, VSWR should be accurate enough.

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[jimbouy]

I might have to take you up on the offer, any discount for offshore members? ONLY JOKING.

I am a little bemused as the so called aerial instructions say the aerial is pretuned and to use at least 7ft of the coax and to then trim 1ft off if the SWR is too high?? Most odd.

I guess I'll see what the old CB job reads first

<hr width=100% size=1> "It is a pleasure to give advice, humiliating to need it, normal to ignore it"

 

[andy01842]

“cb” vswr meters are at best not vary accurate at the frequency that they are designed to work ie 27Mhz at vhf they will only give vary misleading reading. The meter itself will cause a high vswr back to the radio.
Andy


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[William_H]

I had a career in aviation radio installation and maintenance and we used what I imagine is the same as your CB VSWR meter for both HF and VHF. The adjustment to full scale forward takes into account the different sensitivity at VHF so go for it.
The instructions about cutting the coax to get the swr lower is very suspect. If the antenna has a good groundplane ie earthed to the mast top or a metal cabin top then the only way to trim the antenna is to cut the top off the anmtenna fine but hard to revert to the original length. Anything less than 2to1 should be left for on air trials. If you don't have a groundplane and the antenna is not made for operation without one then a substitute can be made by fitting a coax braid over the feed coax from the base of the antenna for a length equal to a quarter wavelength or the length of the antenna if it is a straight rod. This braid is connected to the earth connection at the base of the antenna and insulated for it's length down the coax. PEM if you are confused regards will

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[jimbouy]

Thanks I'll let you know how I get on.

<hr width=100% size=1> "It is a pleasure to give advice, humiliating to need it, normal to ignore it"