Author Topic: CB SWR meter for 2m – quick & dirty trick  (Read 2688 times)

Offline Alan Georges

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CB SWR meter for 2m – quick & dirty trick
« on: June 17, 2014, 10:48:09 PM »
In short, here's the link: http://www.kb6nu.com/no-vhf-swr-meter-no-problem/
In case the link goes bye-bye, here's the main text:
Quote
If all you want to to is check SWR on your 2M antenna, you don’t necessarily have to buy a dedicated VHF/UHF SWR meter. What I keep in my toolbag for that is a cheapie $5 hamfest special CB SWR meter. They really don’t work well on 2M but there’s a trick you can do that will net a reasonably accurate SWR reading on 2M with one of these meters. What you do is connect up the meter as usual, key the rig with the switch in the forward power position, set the adjustment for full scale. Now, without touching anything, swap the coax connections so that the rig is connected to the “ANT” side of the meter, and the antenna is connected to the “XCVR” side. The reading you see on the meter will be very close to your real SWR. The closer to 1:1 your SWR is, the more accurate it will be. It would be more convenient to have a real SWR meter or antenna analyzer if you do a lot of testing, but for a quick antenna check after a mobile install or whatever, the $5 CB meters work OK.

Huh, just tried it on my nice, shiny, checked-on-a-good-meter copper slimJIM, and it read 1.3 – exactly the same as a friend's good meter.  So it does seem to work.

I see a homebrew 450 Ohm ladder line go-bag slim jim in my near future, probably this one: http://www.kn9b.us/slim-jim-antenna 

Offline redeyeprep

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Re: CB SWR meter for 2m – quick & dirty trick
« Reply #1 on: June 18, 2014, 10:22:04 AM »
You might be surprised how often a cheapie meter will work ‘normally’ (just using the fwd/rev switch) at 2m frequencies too. Definitely something to test first. When in doubt, the coax switching trick is probably safer, so long as you can avoid bumping the potentiometer in the process.

Even if the accuracy isn’t there, it’ll still usually be more than adequate to tune for the lowest SWR, even if you won’t know with certainty what the value of that ‘lowest’ SWR is.

Offline Smurf Hunter

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Re: CB SWR meter for 2m – quick & dirty trick
« Reply #2 on: June 18, 2014, 12:48:37 PM »
You might be surprised how often a cheapie meter will work ‘normally’ (just using the fwd/rev switch) at 2m frequencies too. Definitely something to test first. When in doubt, the coax switching trick is probably safer, so long as you can avoid bumping the potentiometer in the process.

Even if the accuracy isn’t there, it’ll still usually be more than adequate to tune for the lowest SWR, even if you won’t know with certainty what the value of that ‘lowest’ SWR is.

To summarize, no matter how off the meter SwR is always rwlative.  So a reading of 1:1.2 is always better than 1:1.5 on a given meter.

Is this accurate?

Offline redeyeprep

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Re: CB SWR meter for 2m – quick & dirty trick
« Reply #3 on: June 18, 2014, 01:13:42 PM »
Generally, unless the meter is totally whacked on 2m. So if I were throwing a cheapie meter in a go bag, I'd want to first compare it's performance against a known meter first. They'll usually work relatively (no pun intended) well though.   :D