How do you test SWR on handhelds?

[DaveC1964]

So I have this Midland handheld that came with the standard rubber ducky. I replaced it with a 51" base loaded antenna. How do I tune that to get best SWR? I think usually those meters go in between the radio and antenna right? I am not sure how I would do that with a handheld, maybe I need some kind of an adapter? Is there a recommended way of doing it?

 

[mmckenna]

Unless you can get the SWR meter in-line with the radio and the antenna, you really can't. Does the CB have an antenna connector on top, or does the antenna mount permanently to the radio?

There's a lot going on, too. On a hand held radio, the SWR is going to be impacted by the user holding the radio (radio chassis coupling into the users hand acting as a counterpoise. Unless you can match all that in, it's kind of pointless. Attaching an SWR meter in the middle of that is going to result in some differences.
The CB walkie talkies themselves won't be hurt by high SWR, they are designed to take it.

Tuning a telescopic antenna would require adjusting how much antenna was pulled out, and getting that right every time might be difficult.

 

[paulears]

Not much point really, because no handheld has a good VSWR, because every radio is too small to act as a groundplane, and the wet bag of water holding it vary in shape, size, mass, electrical conductivity.

in all real world practical tests, the only measurable test is simply that of field strength, as in how string is the signal.

what you can do is get a sheet of metal, drill a small hole in the middle and screw in an antenna to a cable with different adaptors underneath. Then you can with the right gear check where the antenna is resonant, and measure the VSWR. Year back I did some tests using this method and field strength and came to the conclusion that most antennas were dreadful. Crazy claim as for gain, and for those that extended proof they were just an impractical antenna. VSWR readings from that test can’t be duplicated on the radio, because any adaptor, even a small one, wrecks the measurement.

the thing that jumped out was that quarter waves for VHF that work as a ¾ wave at UHf very well. All the clever ones with filtering with coils and capacitors perform ok at. Maybe two frequencies, but are awful at others.

 

[Ubbe]

I have used an empty radio chassi of about the same size as the radio and put the antenna on that and then a coax on the inside goes to the analyser/SWR meter and to the actual radio. I hold the chassi the same way as a radio and measure.

/Ubbe

 

[prcguy]

I have used an empty radio chassi of about the same size as the radio and put the antenna on that and then a coax on the inside goes to the analyser/SWR meter and to the actual radio. I hold the chassi the same way as a radio and measure.

/Ubbe

This is how you do it but also decouple the coax coming out of the empty chassis to reduce the influence of the coax in the measurement.

 

[Ubbe]

The chassi works to some degree as a sleeve balun. I see no changes in SWR or in the antenna analyzers diagram when I touch and move the coax cable, but extra toroids wont hurt.

/Ubbe

 

[DaveC1964]

Unless you can get the SWR meter in-line with the radio and the antenna, you really can't. Does the CB have an antenna connector on top, or does the antenna mount permanently to the radio?

There's a lot going on, too. On a hand held radio, the SWR is going to be impacted by the user holding the radio (radio chassis coupling into the users hand acting as a counterpoise. Unless you can match all that in, it's kind of pointless. Attaching an SWR meter in the middle of that is going to result in some differences.
The CB walkie talkies themselves won't be hurt by high SWR, they are designed to take it.

Tuning a telescopic antenna would require adjusting how much antenna was pulled out, and getting that right every time might be difficult.

It has BNC connector. It is a Midland 75-822 and I have one of those Amazon base loaded telescoping antennas. I wanted to see how the SWR for that compared to the standard rubber ducky antenna which I don't want to use due to those having terrible range. I am skeptical of those aftermarket antennas being tuned right.

 

[mmckenna]

It has BNC connector. It is a Midland 75-822 and I have one of those Amazon base loaded telescoping antennas. I wanted to see how the SWR for that compared to the standard rubber ducky antenna which I don't want to use due to those having terrible range. I am skeptical of those aftermarket antennas being tuned right.

Good advice above on how to do it.

I made a similar device as Ubbe did with an old Kenwood TK-290 that I gutted out. I've used it for years to test questionable hand held radio antennas at work.

Testing with the BNC connector should be easy enough.

Don't chase perfection, though. You probably won't find it. In fact, with the lack of a good ground plane, you may find that most of your antennas are not going to give very good SWR.

 

[merlin]

For the most part, I use a NANO VNA. analyze the antenna, then on the radio, there is little difference.

 

[W8HDU]

The Nano VNA is one such method. Or using RG-58 (stranded) cables to your wattmeter. I was able to do this easily while testing the President Randy II and QYT CB-58, When you test, make sure it's outdoors with the transmit antenna in the clear. If you try doing it on the bench in your shack, you'll get all sorts of artifacts.

I use the same setup for VHF/UHF measurements.

Also, prior to measurement of the antenna, use a RF load to get a baseline for the output.

 

[paulears]

If moving about, or changing hand or radio position doesn't change the results on an analyser, then I suggest it's broken!

Sticking ANY antenna into my analyser and looking at the screen produces the expected dips and spikes, but just rotating/moving in the office clearly shows the interaction.

The upshot of course is that on a portable, VSWR is largely irrelevant. Tuning for antenna match is pointless as most handhelds expect VSWR to be wrong, and just protect themselves where necessary. If you want to tune an antenna (like the telescopic ones) on a portable - then tune by signal strength. Look at the meter/analyser at a distance and adjust till you get the most output. That's where the handheld and antenna combination is working most efficiently. If that has a high or low VSWR on a meter, the meter setup and connection is probably flawed. X Watts in, and X power at a remote antenna is the sensible thing to use to adjust them. With handhelds and bodies offering such dismal balance to the antenna, circulating currents just confuse the measurements.