Now having purchased a low cost vector impedance analyzer, I feel like I have a hammer and everything looks like a nail.
I’ve complained about questionably genuine NA771s before in my SignalStick review but I thought it might be fun to stick them on the analyzer, sweep them out and see how they compare.
Here it is, the N1201SA by Accuracy Agility Instrument.
(bloom is because it’s still got the screen cover on)
- This isn’t entirely scientific. HT antennas are hard to measure because they’re to some extent tuned to be on a handheld, in your hand. I tried to keep things fairly consistent but the phone wasn’t always in the same place. This didn’t seem to change the measurements much.
- I’ve done a second set of 2m tests holding the analyzer in my hand to see the difference. 70cm was pretty much the same but 2m changed a lot.
- Handheld antennas can frequently have very poor VSWR because they’re often undersized. Especially on 2m. Given no feedline, there’s not as much loss from this as you’d think. There’s no “2:1 or better” here.
- VSWR says little about antenna radiation performance. A 50 ohm dummy load is 1:1 VSWR, but a terrible antenna. This is an exercise in characterising antennas not comparing performance.
- The analyzer can’t do screenshots. Sorry.
- The analyzer costs an order of magnitude less (~$300) than a “proper” one. It’s probably not as accurate, but should give you a general idea of what an antenna’s good for.
- The “marker” feature on the graph screen gets a slightly diffrerent result to the single frequency test. It’s not me moving the analyzer, it does this on fixed antennas too.
Antenna 1: NA771 (possibly genuine)?
This one is 390mm long from base to tip, and has silver Nagoya printing, with the NA in Nagoya being in the same font. The back has a QRCode on it to http://www.nagoya.com.tw.
|VSWR 146MHz on table||9.248|
|VSWR 146MHz handheld||2.735|
VSWR on 2m is quite bad until I hold it, then it greatly improves.
Antenna 2: NA771 (definitely fake)
This one is 385mm long from base to tip, and has white Nagoya printing, with the NA in Nagoya being in the wrong font. No other markings are present.
|VSWR 146MHz on table||1.738|
|VSWR 146MHz handheld||2.211|
Maybe someone tuned this based only on the analyzer, and didn’t check it in a handheld, because the antenna gets worse on 2m when I hold it.
Also, you can see from the graph that it’s very different to Antenna #1.
Antenna 3: NA771 (definitely fake)
Looks exactly the same as Antenna #2. #1 and #2 came from one seller when I ordered 2, #3 and #4 came from another - yes I got different antennas in the same purchase and the seller claimed both were genuine even though they were clearly different.
|VSWR 146MHz on table||1.710|
|VSWR 146MHz handheld||2.759|
The curve looks like the other one but there are differences in the VSWR readings. Tried to be pretty careful about holding the analyzer in the same way.
Antenna 4: NA771 (definitely fake but different)
Another fake NA771 here. Nagoya branding is on a foil sticker. Antenna is noticably longer than the others, at 410mm.
|VSWR 146MHz on table||6.638|
|VSWR 146MHz handheld||4.201|
VSWR is significantly worse and 70cm is way off (and doesn’t get better when I hold it). The second is near 220mhz, so maybe this is a dualbander for the wrong two bands. I do recall this antenna being worse on 70cm and now I see why. It’s amazing how much these four antennas differ.
Antenna 5: SignalStick
Let’s put the SignalStick through the same test to get some numbers to compare and contrast
|VSWR 146MHz on table||2.887|
|VSWR 146MHz handheld||1.765|
The SignalStick has a higher VSWR at 430MHz - but this may be due to a lack of active matching at this frequency. I believe the NA771s are tuned to be a dual 5⁄8 at 70cm, with the SignalStick being a 3⁄4 wave. In the real world it seems no worse at 70cm, and much better on 2m.
As it’s made of nitinol wire, you can of course coil it up. I wonder how it performs…
Well, the VSWR isn’t bad - in fact it’s better than when it’s uncoiled, but I do wonder what the radiation pattern would be…