Add on antennas for hand-held - forthcoming tests

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Add on antennas for hand-held - forthcoming tests

Postby G4RMT » Sun Jan 21, 2018 6:15 pm

I've got back home after Christmas and have a nice pile of antennas waiting for testing. Basically I bought a dozen fairly randomly and all designed for hand-held with crazy titles like "hi-gain" and others with gain figures - either in useless 'dB' measurements or "dBi". Lots are labelled dual band 144/430MHz - when they are UHF quarter waves, so useless on VHF. I've got two identical ones from different suppliers, and Googling the forums it is possible one is a genuine ~Chinese brand name and the other a copy, but I suspect they're both just Chinese antennas of a similar design - and one or both could be genuine or fake. The very strange thing is that the quarter wave physical length for VHF and UHF is simple to calculate, and the ones on my Icoms and Yaesus seem to be around this length - but none of the Chinese ones are the usual lengths for the ham bands!

Sticking them all on the analyser brings back some very strange resonance frequencies!

So far - they're all cut too long, or in some cases too short. Quite a few hint at being more suitable for receivers. Some are clearly not what they say - Dual band is emblazoned everywhere, yet few are anything other than ¼ waves at VHF, and therefore ¾ waves at UHF. Specs always seem to hover at the mathematical 2.15dB figure - as in a quarter wave performance, yet only a few actually specify 2.15dBi - as in 0dBd. Lots of smoke and mirrors. Some are certainly very thin, or very flexible, and one of the telescopic ones getting on for a metre long with a coil half way up. Completely useless for a portable as with their known antenna socket issues, I doubt any of the Chinese radios can support one of these monstrosities safely. It does, however, appear to be one that may well have true gain over a dipole.

Next step is testing them. I've decided to measure the improvement over the stock antenna supplied with the radios. My testing setup is going to be practical. Radio in a set position, then a stepped attenuator in line with a receiver. No CTCSS, and then reduce the signal from a Wideband antenna until the squelch closes - on the stock antenna. Replace the stock antenna with the series of test antennas, one by one and see how many dBs of attenuation are required to let the squelch close. This will give an indication of how much better the replacement antenna is, compared to the stock one. I'll also check each radio's stock antenna against a common quarter/three quarter wave cut to the test frequencies.

As the common radios could be used on ham bands at the bottom to business radio at the top, I'm going for half way - Marine band and 446.

So far - I'm convinced that most of these so called 'better antennas' aren't. Any differences are going to be very small. Where there is a difference, it seems to be related to the length. Looking at the plots on the analyser - third harmonic performance is how they get their dual band tag, not by any clever design. Some have quiet substantial bottoms - close to the connector which could contain a coil making a 5/8th design physically possible but the whip lengths have no mathematical link I can see, and while a 5/8th at UHF could be possible on a couple, the resonance plot at VHF would then look different. Most, it would appear are simply physical moulding around the join between connector and whip - nothing more.

On the subject of branding - Nagoya and Diamond are quite well known brands, but I can't comment on the brands here in terms of them being genuine against fake. The brands could simply be printing on the antenna and plastic pocket they are supplied in. The one labelled Baofeng in the advert has no name at all on the actual antenna.

I do have a dual band Icom portable antenna somewhere dating back to the 80s, supplied with an IC-32. If I can find this, I'll test it too and hopefully use it as a comparison. I'll also see what the difference in performance is of the two antennas supplied with the TYT 380S - The quarter wave and the shorter helically wound one.

I'll start the testing as soon as I get some time. I have a spare couple of Kenwood repeaters in the rack, so I'll programme these up to do the receive function. At the very least I should have a top ten or twelve of commonly available antenna that people can then consider before spending their money.

The antennas that will be on the bench are these.
SAINSONIC INF-641
OEM RH-770
OEM HIGH GAIN
SAINSONIC INF-661
NAGOYA NA-774
NAGOYA NA-771-Orange packaging
NAGOYA NA-771-Green packaging
DIAMOND RH-771
NAGOYA NA-701
BAOFENG TELESCOPIC - green band
NAGOYA NL-R2
DIAMOND RH-901S
RETEVIS RHD-771
OPPXUN 669C
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Re: Add on antennas for hand-held - forthcoming tests

Postby G4RMT » Sat Jan 27, 2018 11:19 am

Update
I'm finding that the radios are playing a vastly more critical role than I imagined. Results from the first test were making little sense, and what I have found is that the small radios are much more prone to loss of efficiency because their ground plane is so tiny - holding them in the hand next to the body has a much more beneficial effect than with the bigger radios with more metal in them! So the test results were poor when standing alone on the bench. So I've changed the testing methodology. I've cut an aluminium ground plane that each antenna under test can be connected to so the measurements have a common element - an identical ground plane. One other thing I'm discovering on the cheaper radios is that while doing the initial testing for the testing, so many of them are very good at receiving with no antenna connected at all! They also radiate quite well too! Connected to external antennas, I discovered that the RF in the room when transmitting was messing up some of the sensitivity measurements. Sticking a couple on a dummy load in one room on low power was still enough to be heard in the room next door. I tried the same test on a Motorola and two Icoms with 20 yrs between them, and on the dummy load, stray RF leaking was virtually zero. I tried the same test on a Chinese mobile, with metal case and it too is very happy receiving signals NOT through the antenna connection.

I now have the antenna for transmit on a ground plane, with the radio inside a faraday cage (well, a biscuit tin). This makes the measurements reliable.

I have discovered one of the radios I'm using for receive has a signal strength meter that is a bar, plus a numeric display - which I'd not noticed. I can calibrate the readings to specific signal levels from the generator, and it's not quite linear - but it makes using the variable attenuator more accurate so 1dB actually is 1dB. I've got to scrap the first set of results , and I also need to replace an attenuator - It's clearly limited in accuracy once I go above VHF, so I've ordered a new one flat to microwave.
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Re: Add on antennas for hand-held - forthcoming tests

Postby LandingGearLaurie » Sat Jan 27, 2018 11:38 am

I’m following this post with great interest!

Please keep it going!
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Re: Add on antennas for hand-held - forthcoming tests

Postby m0lsx » Sat Jan 27, 2018 12:26 pm

G4RMT wrote:Update
I'm finding that the radios are playing a vastly more critical role than I imagined. Results from the first test were making little sense, and what I have found is that the small radios are much more prone to loss of efficiency because their ground plane is so tiny - holding them in the hand next to the body has a much more beneficial effect than with the bigger radios with more metal in them!


When I first stated playing with 4 meters, I used an old ex Fire brigade Pye PFX & as someone who was use to the ATX & wonder wand antennas as used on the FT-817's where the ground plane made a world of difference, I followed what I saw someone else do & started using a tail & found that a simple 2 meter length of wire connected under a screw that went to the Chassis made far more difference than any antenna change could.
It might be my imagination, but I am sure even my FT-290 seems to perform significantly better when a meter of wire is connected to it's chassis. I have a tunable counterpoise that I use on the 817.
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Re: Add on antennas for hand-held - forthcoming tests

Postby G4RMT » Sat Jan 27, 2018 4:35 pm

I figured that handhelds used the body - pretty obvious, but although I haven't proved it yet, I'm wondering if the body effect has been forgotten - or maybe the manufacturers are exploiting it when they match a hand held with it's stock antenna? All those youtube videos testing range winding the window down, when sticking the radio on the roof would have made mega difference to the range.

I shall report back if I find anything else before doing the proper tests. I didn't expect this to be as complicated to sort!
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Re: Add on antennas for hand-held - forthcoming tests

Postby m0lsx » Sat Jan 27, 2018 5:09 pm

G4RMT wrote: I shall report back if I find anything else before doing the proper tests. I didn't expect this to be as complicated to sort!


Yes please, it's all interesting stuff.
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Re: Add on antennas for hand-held - forthcoming tests

Postby G4RMT » Wed Feb 07, 2018 11:31 pm

Ok - results are in.
https://vimeo.com/253257805

Not the results I expected at all. Most of these antennas are labelled high gain, and some have gain claims - some say 2.1dB/3.2dB gain or similar and so few of the antennas I tested have any gain over that from a quarter wave. Those that do have a bit off gain manage a tad less than 3dB, and only at very specific frequencies - the ham bands. They're all labelled as dual band, but many are rubbish at one of the bands they cover. One struggled so badly, that even with the attenuation switched out, I couldn't get the test level at the receiver.

I have taken 7 frequencies from VHF to UHF - common ones people will be using. I've set up a jig so I can swap out the antennas, and am using a single transmitter, with attenuator and VSWR/power meter in line. At the other end is an outside antenna - mounted at the same height as the test antennas, separated by just over 10m. This antenna feeds a receiver that has a numeric readout of signal strength. The antenna is fed to this via an adjustable attenuator. Each test entailed gradually adjusting the attenuator until the signal strength was the same. I picked a setting of 70 on the meter, and in this area it's response was linear - 1dB on the attenuator would drop 70 down to 69, and removing 1 dB would drop the reading down one. All I had to do was produce 70 on the meter and read off the dB setting and record it in a spreadsheet. The only issue I found was that the chosen antenna was less sensitive at UHF, so the readings for UHF were different too VHF. The quarter wave test antennas produced 40dB attenuation for 70 on the signal strength meter for VHF, and 23dB for the UHF band. A higher attenuation figure is indicative of real antenna gain. So if the attenuation was 43dB - that's a 3dB gain figure. Sadly, the only antennas that produced gain were just at the amateur frequencies, and moving just a little away, removed all the gain. Some really struggled to do well at both bands, and some were really awful.

The interesting bit was the Nagoya 771 - two versions were sourced and one is commonly talked about on the net as being a counterfeit, and the other one genuine. I really don't know - but they do perform differently. The results seem pretty conclusive. Many of these quite large antennas are actually very similar to the stock antennas - and a full quarter wave - 19" long still works the best. Not included in the video, but tested are the ones supplied with the GD-77 and three different Kenwood types. The stock GD-77 is pretty good, as are the Kenwoods supplied with the cheaper 2000 and 3000 series radios. The shorter one on the Kenwood Nexedge radios was shorter - and clearly worse.

When I get the chance I'll put the spreadsheet with the full data on myself ever and post the link to it.

It took me a long time to collate the data - a lot longer than I thought. Some interesting results I think.
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