Just for fun, I tried connecting the rubber flex antenna from my Yaesu FT-70D handheld directly to the SMA connector on my NanoVNA (after calibration) and seeing what the characteristics were. I was pleasantly surprised on 2m.
I figured that holding the VNA as shown would pretty closely simulate the same effect as holding the HT, and that seems to be the case. The resonant frequency did vary with the position of my hand, but it stayed pretty well within the 2m band. In the photo, the marker is at 146.0 MHz, SWR is less than 1.167 at minimum, impedance is approximately 55 ohms.

On 70 cm, though, I found it to be much less cooperative. at 445.2MHz, SWR was about 2.8:1. Impedance reads 51.6 ohms net, but very capacitive (32.7 -j39.9 ohms) I'm not sure here whether being mounted to the HT would make a difference, and it is difficult to measure with any sense of accuracy.

Nice. Better results than I got... But no dual band antenna is equally good on both bands.

A handheld radio will work perfectly well over a huge range of antenna SWR as they are designed to do just that

SWR is mostly a feeder /loss issue but there’s no feeder

Different rules to base radios

Not entirely true, some are better than others, and others, usually fakes, are terrible. Fortunately, as stated, most handhelds are fairly tolerant of a high SWR, but that's not to say that the antenna is actually radiating efficiently.

However, in all case the performance is determined by the antenna position relative to your body, and also the extent to which the radio provides an adequate ground plane. Most have a metal body or sub-chassis for better heat sinking of the PA device, and this helps to stabilise the antenna feed point impedance.

Try connecting a 1/4 wave wire to the outer of the SMA connector and see what difference that makes.

As a further test, see if you can find an on-line websdr that can receive your signal, and then have a look at the digital signal strength meter that is calibrated in dB. You may have to move the handheld an antenna around to "peak" the signal, and this will vary slightly with each one, but you may be in for a surprise.

Here are some typical results using different antennas on a Baofeng UV5 dual-band handheld. Using the "Long Flexy" (genuine Nagoya NA-771 - beware of fakes) as a reference. They all present a reasonable match on both 2m & 70cm.

Antenna "Stubby" "Short Flexy" "Long Flexy"

2m -9dB -2.5dB 0dB

70cm -6.5dB -3dB 0dB

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Regards,

Martin - G8JNJ

"... online websdr that can receive your signal..."???

I know about these for HF but they exist for VHF/UHF?? There would have to be a lot of them! 🤔🤔

It depends on where you are located, but there are quite a lot of them covering VHF / UHF

http://www.websdr.org/

map view at the bottom of the page

Also

https://www.receiverbook.de/

Map view

https://www.receiverbook.de/map


And of course the short wave bands too.

http://rx.linkfanel.net/

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Regards,

Martin - G8JNJ

Amazing! Thanks for the links!

Testing a Rubber duck with a VNA is useless. The HT chassis is half of the antenna. so without the HT chassis the antenna is not going to be anything close to what it is on the radio.

Joe WB9SBD

True ish.

The radio chassis and battery are indeed designed to couple to the users hand

And small VNAs, are a bit bigger but less designed for coupling

You can test how sensitive an antenna is to this by extending a finger onto the antenna connector

But as I keep saying doing mobile radio (portable) development the main use case requires field strength and a near omni pattern over a particular business band - so 90% of the time was working on that and the SWR result was interesting but not that interesting if a worse SWR worked better in the field

PAs overrated and up for 10:1 and more

Hi Bruce,

Agreed, assuming the radio presents a 50 ohm source and the antenna is a 50 ohm load, a 10:1 SWR ratio would equate to approximately 5dB mismatch loss, and 3:1 would be only just over 1dB.

However, as you state, unlike in theory and with signal generators, most transmitters do not have a "genuine" 50 ohm output, they are simply designed to transfer power to the antenna as efficiently as possible, and not all antennas are exactly 50 ohms resistive.

As a consequence, there will be some interaction between the two, and 50 ohm SWR or Return Loss does not tell the whole story.

Monopole and whips should in theory present an impedance of less than 50 ohms at resonance, but this value is often modified by their construction, internal matching networks, and various internal and external losses.

50 ohm coax only became in common use after the various technological improvements made during WWII, filtered own into commercial products, and 50 ohm coax became more widely available. Prior to that, many other impedances were common in antenna designs.

It is perfectly possible to design both the transmitter and antenna to have a different characteristic impedance, and although 50 ohms tends to be the common standard, don't assume it is always the case.

Field strength tests, and A/B comparisons, are often much more revealing than just measuring the SWR. I think if more people tried such things, a lot of antennas, primarily those sold to radio amateurs, would be found lacking.

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Regards,

Martin - G8JNJ

Martin.

Well said. I think Motorola used nominally 90 or 100 ohm whip antennas for a while on some of their handhelds ..

Never had time to dig into this