On the HamRadioHelpGroup mailing list, a ham asked:
Will a CB SWR meter work on a 2 meter ham radio??
Mark, K5LXP, replied:
Yes and no.
I use a CB SWR meter to check 2M antennas all the time. There is a trick to it however.
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.
When I asked his permission to use this, Mark said, “I don’t get the credit, I picked it up from some OF years ago.” (E-mail me if you don’t know what an OF is.) Well, Mark, you might not get the credit for thinking this up, but you certainly get the credit for passing it on. Thanks!
Very clever. Thanks for passing that on. I never have understood why HF SWR meters are a dime a dozen but VHF ones are so hard to track down.
I would buy 10 dozen if they were just a dime a dozen.
I have an old CB SWR meter and I have a slew of 1N34A Point contact diodes for VHF frequencies. Can I replace the diodes in that meter with these diodes?
A sido de mi inquietud y realice una comparación de estos componentes y si funciona 1n34a o 1n5711 o 1n5712 estos dos últimos mejoran la lectura de potencias bajas
73 ti4dmr estas referencias provienen de esquemas y comparación de circuitos de tuner y swr meter MFJ de casi todos los tipos
A further comment from K5LXP gives a little deeper technical explanation:
What about 220 mhz and 440 mhz ? Any meter tricks for those freqs. ?
I have a 220MHz rig but no SWR meter for that freq.
Dan,
I have found that the old Micronta CB 3 range power/modulation/SWR meters work quited well on 2 meters (probably better than they did on 11 meters). These are the 3 dial meters left to right power 5/50/500 watt range, modulation and SWR. The SWR and power meters are accurate within about 3% when compared to my Bird meter on 2 meter FM. Never tried it with SSB though. I have two of these and both read the same, so it is probably not just a coincidence.
Jack KG4MFJ
One quick question.When setting the hf swr meter up in the forward power position is the swr meter connected to the antenna of unknown swr or to a 50 ohm dummy load as usual?
Thanks
Thomas
You connect it to the antenna. That sets your reference for the reflected reading.
Thanks for the reply.
73’s
KB4CJD
Thank you very much for this information. Money is tight and I have a little HF meter but didn’t want to buy a separate VHF meter.
Thank you it worked for me.
I’m interested in the air band, 118-137MHz. Can a CB SWR meter be used as suggested on this page with any expectation of accuracy?
You really think keying up on Airbands to check SWR is a good idea
I’d expect when you do a whole bunch of people will be kicking in your door to help solve your issue
They might, if the ham bands were so crowded that there were no open frequencies. Unfortunately, that’s not really the case. There are plenty of open frequencies where this kind of testing can be safely carried out without interfering with anyone.
If you use it in the manner described, yes, it will be accurate. Are you going to be transmitting on this band? If not, then you don’t really need an SWR meter.
In my case yes, I recently bought a plane and discovered that it has a wingtip antenna built in. Turns out to be a mod that a guy named Bob Archer sold back in the 60’s. It’s not a typical dipole design, not a dipole at all in fact. It integrates the balun into its design. According to Archer, who I was able to track down, it should have a VSWR of about 1.5. Anyway with age and such I’m not so sure about it. It seems to have decent range but the reception is not always as clear as expected and occasionally I also have to repeat.
So short answer, yes :)
Sounds like some testing is in order then. :) I’m sure you know this, but I’d suspect bad connections first.
…funny how most would assume instantaneously that you werent into aviation and had a plane with a radio , where you are legally allowed to TX.
Update: I measured the wingtip antenna and got about 1.5:1 as advertised. That was kind of shocking so I measured the whip dipole and got 2.5:1. This is consistent with new antennas, so I guess I got an accurate measurement. If signal loss is within specs, does that disqualify the antenna, coax, and connectors as possible problems?
No. Lossy coax will actually make the SWR reading look better than it should. Think about it. If the feedline is lossy, the meter will measure less reflected power.
I have an old Lafayette 99-26395 Power/SWR. It has a power meter, a SWR meter, and a tuning knob that goes from 0 to 10. It does not have a forward/reverse switch and the coax connectors are not labeled. I have no idea how to use it! I was unable to find any information online as to how to properly use it. Are you familliar with this meter??
Thanks!
Hi, Roger–
I have a very similar meter, the Quement SWB-3. So similar, in fact, that I wouldn’t be surprised if the same Japanese company made both meters. Basically, to measure the SWR, you adjust the pot so that the power meter reads full scale. Then, you can read the SWR directly from the SWR meter.
To measure the power, you have to set the pot to a pre-set position. This is different for each band. Needless to say, this measurement is not very accurate.
To get the manual for the SWB-3, go to http://bama.edebris.com/manuals/quement/swb3.
73, Dan KB6NU
I will guess “OF” Was short for Old Fart.. Meaning some old guy back when..
LOL. Best guess I could come up with.
Great little tip! Been testing out all the VHF antenna’s I built. Do not want to invest in a dedicated VHF SWR meter since I am going to get an antenna analyzer. But I have this old hand me down HF meter here. Thanks
73, Dave N6DLH
So will this method work for dialing in an FM antenna for a Low Power FM transmitter?
Thanks,
Mike
It sure will!
Just got my first 2m rig. Got the antenna up a day before the snow. With no way to test it, I have just been listening. Used your method with an old HF meter, and see that it is OK to transmit. Thanks for this tip.
Wonderful! I’m glad this posting was helpful.
I dont understand, we are susposed to swap the connections so they’re backwards while still transmitting? Isnt that really bad?
You would think so, but not really. Take a look at the schematic at http://freecircuitdiagram.com/2010/12/29/simple-swr-bridge/. This is similar to the circuit you’ll find in most of these cheapie SWR bridges. It’s pretty symmetrical no matter which way you hook it up.
Ok, I get the theory now, just need some help on the procedure… So the correct step by step procedure would be to
-attach transmitter to transmitter, and antenna to antenna.
-Make sure switch in on forward, transmit and adjust to read full.
-stop transmitting and swap antenna and transmitter connectors
-switch to ref and transmit to see swr
Is this right?
Thanks for the help!
No! You always leave the FWD/REV switch in the FWD (forward) position. When you connect the antenna to what is normally the transmitter connector and the transmitter to what is normally the antenna connector, you’ll be reading the reflected power only if the switch is in the FWD position.
I received my tech. license about a month ago. I put up a discone antenna with the stinger and 4 ground plane radials removed for use on 2 meters. I used the good 50 ohm coax. I have a cheap Radio Shack SWR meter and cannot get the meter to calibrate. The needle will go about 3/4 of the way to the calibration mark but no further with knob turned completely clockwise. Help. What am I missing?
This trick can be extended to 440 but I got fooled badly while tuning a 440 J-pole by moving the connection points up and down. I couldn’t get a low VSWR no matter what I did.
After hours of frustration, I disconnected the j-pole and substituted a dummy load on the ANT connector of the meter. It read about 3:1!
Obviously, that particular meter, though fine for HF and okay on 2m, could not read 440 reliably. As soon as I got a different meter (and tested it into open, short and dummy load) I had my 440 j-pole ready to go very soon after.
Most of my meters are now clearly labeled with the bands on which they will provide useful indications.
I read this over twice and read the comments as many times. One was seemingly unanswered.
Greg says: April 27, 2012 at 11:31 pm
I dont understand, we are susposed to swap the connections so they’re backwards while still transmitting? Isnt that really bad?
If I understand correctly (and I may not) prior to switching the XCVR and the ANT connections, you un-key the XCVR, swap the connections, and re-key after switching connections and read SWR? This is an old thread and you may not be following it any longer.
Dan KB6NU Thanks for the info already supplied. You had me dig up my old OLSON Electronics CB 67 meter. Took a while to find it.
No, you don’t swap the connections while still transmitting. First, you connect the meter between the rig and antenna in the normal way. Transmit and set the meter to full scale. Second, stop transmitting, then swap the rig and antenna connections. Third, transmit again. The meter should be reading a value that’s very close to the actual SWR. Does that make sense?
I had the same misinterpretation. The post states “Now, without touching anything, swap the coax connections”… this sounded to me like you weren’t supposed to un-key the transmitter,, I was shaking my head ? HUuh?? Thanks for asking for the clarification, even against what one might aof a logical. And thanks for the idea Dan.
73 or (73’s,,, multiple, multiple, multiple… best regards) hihi
Yeah, saw this was an old thread, but saw you answered 23Oct2015. Thanks for such a brilliant idea for being cheap, (like me!). Hope you don’t mind if I share this site with a few of my fellow hams. Thanks again sir.
KM4NTX
After reading the comment above from John KD6VKW, I wonder if this might work for 440 if you go through the procedure using a dummy load in each direction, instead of an antenna. Whatever the meter reads when you measure reflected power, would that be about 1:1 SWR? Then you connect the antenna and tune it to that reading?
What do you think?
This is a smart and useful idea. I saved time and money. Many thanks.
I recently purchased a roof-top antenna for my car (Nagoya UT72, 19″), and am being told over a 2m repeater that my transmissions are weak and at times garbled. I have a CB SWR meter, and will give this a try. I’m using a Baofeng UV5R HT as transceiver.
Patrick, any result with this method?
What a great tip – many thanks! It sounds counter-intuitive until you look at the circuit diagram – it is indeed a virtually symmetrical design.
One thing: wouldn’t it add to the accuracy of the overall measurement if I took an SWR reading as per normal, and THEN took a reading using YOUR technique; and take an average of the two?
I can’t take any credit for this. I got this idea from Mark, K5LXP, who got the idea from someone else. As to your question, no, I don’t think averaging the two readings would make the measurement more accurate.
Hmmm…I got full deflection and more then brought it back to where it should be on the line.
So far so good..swapped the leads and pressed transmit and it went full deflection.Huhh?
What does that mean?
Should this technique also work if testing a 6 meter antenna’s swr?
I don’t see why not.
I have a mfj MFJ-945E antenna tuner is there any way I can use that for 2m ? (without screwing it up)
Unfortunately, not. They just aren’t designed to operate on 2m.
I meant to say to use it just to check swr with tuner in bypass. The answer still might be no but I wasn’t clear.
I don’t see why that wouldn’t work. Give it a try!
I tried it on a Royce Model 2-100 Mhz SWR meter. I set it up with the Forward Full Scale as you suggested, but then when I reverse rig/ant inputs, and then key it again, the meter tries to go to the left of ‘1’ and so you can’t read it.
Is the FWD/REV switch in the FWD position? It should always be in the FWD position.
I know this is an old post but it saved me about $75 over purchasing a 2m swr meter. I had heen getting high swr readings on my 2m amplifier and using this i traced it back to a bad antenna splitter. Great tip. :-)
Old post or not, this method still works!
Most modern transceiver has forward and reflected (or ‘SWR’ meter settings). The SWR meter is the BEST place to adjust tuners for lowest SWR because these are usually a measurement of the SWR at the final stage rather then somewhere down the line.
Thanks, the tip came in very handy since I had lost or sold all my VHF equipment and all of a sudden found a need for at least a meter to test a compact 2EL Yagi for VHF that uses a folded dipole to keep its boom length down to one foot. It turns out that I was close and trimming only took off about 1/4 inch off the Fed element according to the tip. Not sure if the cheap CB meter gave a proper power reading but I did not care about that I just wanted minimum reflection.
Wow, thanks for passing that along. I plan to build 2 antennae for my 2 meter radio and will need to check the SWR on both antennae. I have an old Midland CB SWR meter and if what you say is true, I’ll use it on my antennae.
It’s important to check the other CB radio when tuning the CB antenna without an SWR meter. In order to set up certain spaces from your vehicle’s CB, you should first test on with this CB. Asking for assistance from a nearby person or using a smartphone are both options if you run into problems.