Antenna question - handheld transceivers - about SWR readings on factory antennas

Gadgeteer2000

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Hello all, I have several handheld transceivers. Just for the fun of it, I measured the SWR (with my Nano VNA and with a Surecom SW-102S SWR meter) for the different antennas (factory ones and ones I bought later).

I have found that the antennas (including the factory supplied ones) have SWR values in many cases well over 3 in (large) parts of the transmission range.

I am a newbie about this - but my understanding was that the SWR should be below 2 to avoid damage to the radio. None of the antennas had that for the full transmission ranges of the radios (I tried 6 different models, including highly rated Diamond etc. antennas) .

Is this going to cause a problem with the radio? Or is the high SWR just reducing the transmit range but has no effect otherwise since the output power is not very high?

(The radios I am talking about are 5W - 8W max power)

Thank you for sharing your experiences
 

nd5y

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Hand held radios can withstand high SWR. If that wasn't the case then they would all be damaged in a short time.

Most VHF and UHF hand held antennas are an electrical 1/4 wave which requires a ground plane or counterpoise to work properly. You don't have that with the antenna mounted directly to the radio. Your hand makes a partial lossy ground plane or counterpoise but it's not that effective. End fed 1/2 wave and coaxial or sleeve dipoles don't need a ground plane but there are not many of those made for VHF/UHF.

If you transmit with the radio on your belt or in a pocket with the antenna against or close to your body then the SWR will be even higher. If that damaged the radio then most public safety users would constantly have damaged radios.

High SWR doesn't automatically mean reduced range. Some systems use antenna tunners to match the actual antenna impedance to 50 ohms.
 

mmckenna

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Excellent reply from ND5Y

I have an Agilent spectrum analyzer at work with built in tracking generator. It acts like a very accurate nanoVNA type device.
I can mimic your results with $20K+ equipment.
But as ND5Y said, there's more to it than just connecting the antenna to the nanoVNA...
The radio chassis provides a ground plane/counterpoise of sorts. Smaller radios don't provide very good counterpoises at lower frequencies, especially VHF. They can work pretty well on UHF, 700 and 800MHz.
And, as said above, capacitive coupling to the body through the hand makes a difference.

To test this, I took an old Kenwood TK-290 hand held VHF radio and removed the guts from it. I left the radio chassis and the antenna jack. I connected a length of coax to the antenna port so I could test the radios in a real world sort of situation.
That showed SWR much lower than just the antenna floating in free space.

Still not outstanding low SWR, but something in the 2:1 range or so.

But, as Tom mentioned, the radios are designed to handle that. High SWR on a portable radio, or even a CB, isn't going to result in a miniature mushroom cloud emanating from the radio as the final transistor goes up in smoke. More heat will be generated, but that's about it.


Also, some cheap Chinese antennas sold on line are often tuned no where near the frequencies they are sold for. Taking a good name brand Motorola or Kenwood antenna will show that they are. But take a cheapy e-Bay special, and you'll see then all over the spectrum. One reason why spending a bit more for legit name brand antennas can be worth it.
 

radiosniffer

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NDY5 excellent post.
I too did some SWR testing today with my bucket of antennas. A few (i assume fake nagoya antennas were 19+ on swr meter...ouch.....
I had one authentic nagoya and it ran between 1.1-1.9.
Using a hand held.
 

nd5y

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The best way to test HT antennas is field strength measurements against a known standard on an antenna range.
SWR is almost meaningless.
A VNA tells you the impedance and return loss at one frequency or over whole band but that doesn't tell you how good the antenna actually radiates.
 

prcguy

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Yes on this. Also, when checking VSWR on hand held radio antennas you need box that is a similar size and shape as the hand held radio chassis with a connector in a similar spot as the HT and you must decouple the RF cable to the generator or analyzer so it doesn't become a counterpoise and skew the measurement. The test cable to the radio test chassis will skew both the VSWR and field strength measurements if not decoupled.

You can usually use a scaler or vector network analyzer for field strength measurements. Its best to use a directional antenna at the signal generate side like a Yagi for single band or a log periodic for multiband antennas and use the radio test chassis as the receive side. You can't really do an absolute gain measurement in dBd or dBi but you can get precise gain over a reference antenna that you choose. For example, the last time I did this was with a stock antenna for a Baofeng UV5R and I used that to compare with aftermarket replacement antennas. Sweeping with a vector network analyzer gave me simultaneous VSWR and smith chart info on the antenna under test along with the gain over a wide frequency range for the aftermarket antennas compared to the stock antenna.

The best way to test HT antennas is field strength measurements against a known standard on an antenna range.
SWR is almost meaningless.
A VNA tells you the impedance and return loss at one frequency or over whole band but that doesn't tell you how good the antenna actually radiates.
 

Firekite

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For example, the last time I did this was with a stock antenna for a Baofeng UV5R and I used that to compare with aftermarket replacement antennas. Sweeping with a vector network analyzer gave me simultaneous VSWR and smith chart info on the antenna under test along with the gain over a wide frequency range for the aftermarket antennas compared to the stock antenna.
Now I’m curious about the results.
 

radiosniffer

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haha
Well I reread ( SWR is almost meaningless)....I think I understand that.. :)
 

radiosniffer

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End of the day, I will do field testing and use a good Spectrum Analyzer to visualize/measure my radios and antennas.
 

paulears

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Field testing is probably the only way to get meaningful results. A constant location and path to somebody who can read off your strength on a meter. Remember that the only repeatable perfect 1:1 match is a 50Ohm dummy load that soaks up every bit of signal you output.

if you have an analyser with a tracking generator, the results are often quite strange. I like that idea for an old empty radio case.

I did some a video of some after-market antennas, and to get the comparisons stuck them all on a groundplane. But that’s not real. A long antenna on a tiny radio will have wildly different VSWR, and this changes the test conditions. I suppose a tiny hand held radio held by a fat person might out perform the same radio held by a thin person.

the designers of commercial radios know they will have broken and bent antennas, stuffed into pockets and sat on. They might even be used with the antenna missing. The radios have to handle it. The analysers, like VSWR meters give you clues. Signal strength at a distance is the only thing that matters really. If you get poor range, the test kit is good at explaining why. It rarely predicts longer range.

antennas are still magic!
 

AK9R

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IMSAI guy thinks you can connect handheld radio antennas to a VNA and wave them around in the air while taking measurements:
 

paulears

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Oh MY God! I remembered in my youth the radios the Police had here in the UK and I googled the radio so I could stick up a picture here - and I found ......... me! Click the link - I made it small to save my embarrassment.
Oh no!

The ironic thing is I now live in one of the houses in the background. I reckon this was 40 years ago or close. Feel sorry for me - I was young and didn't know this article would be on the internet from an ancient magazine!

The point though was that the British Police used those dinky helicals and they worked pretty good. The pocketfone had a tiny piece of plate inside for their antenna - not even anything to poke out. I can't say more, I'm in shock!
 

prcguy

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Oh, what a well dressed and proper looking chap! Any mum would be proud of that.

Oh MY God! I remembered in my youth the radios the Police had here in the UK and I googled the radio so I could stick up a picture here - and I found ......... me! Click the link - I made it small to save my embarrassment.
Oh no!

The ironic thing is I now live in one of the houses in the background. I reckon this was 40 years ago or close. Feel sorry for me - I was young and didn't know this article would be on the internet from an ancient magazine!

The point though was that the British Police used those dinky helicals and they worked pretty good. The pocketfone had a tiny piece of plate inside for their antenna - not even anything to poke out. I can't say more, I'm in shock!
 
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