How to check VHF-vs-UHF rubber duck?

Status
Not open for further replies.

Rred

Member
Joined
Nov 21, 2014
Messages
830
My h/t doesn't have an SWR display, and I don't have an antenna analyzer that can reach into the 440+ range. But I do need to test some rubber duck antennas that might be VHF, might be UHF, might be dual band.

Am I missing any simple ideas that would confirm which is for what, and maybe even what kind of swr to expect from them?
 

jaspence

Member
Premium Subscriber
Joined
Mar 21, 2008
Messages
2,359
Location
Michigan
The SMA connector antennas I use have a washer shaped plate around the screw connector that give this frequency of the antenna. This won't work on a BNC connector, but a SWR meter using low transmit power (to protect the transmitter finals) might work.
 

Rred

Member
Joined
Nov 21, 2014
Messages
830
I would like to actually test them, since counterfeit antennas are so common and labels often aren't there, even on OEM antennas. Some are color-coded, yes, but then again the more popular ones are often said to be counterfeited and since some of these are from used equipment of varying sources, I want a simple way to be sure of what they are.

zz-
What are you suggesting? Check them at 144 and just presume whatever doesn't show a low SWR "must" be 440? That's kinda half the job, yes. Still doesn't tell me if the other half are really better suited for toasting marshmallows when there's no campfire.(G)
 

ko6jw_2

Member
Premium Subscriber
Joined
May 18, 2008
Messages
1,128
Location
Santa Ynez, CA
The results of testing these types of antennas may be problematical. I have an analyzer that goes up to 512Mhz. As an experiment I put various antennas on the top of the analyzer. The theory is that the analyzer was a simulated H/T. The results were disappointing. Most of the antennas did not have a strong resonance anywhere. This was true even for very expensive antennas that were "hand tuned." Yes, you want to use the correct antenna, but even with testing the results are disappointing.

I also have some handheld scanner antennas that gave similar poor results.

Maybe you should just order an antenna from a company like Smiley that will custom make the antenna if required.

They are all compromises and you will never get a reasonable SWR off of most.
 

Rred

Member
Joined
Nov 21, 2014
Messages
830
k0-
It would cost way too much to replace every possible antenna in question with a 'correct' OEM antenna from the actual OEM's authorized distributors. I'm sure when my local radio shop orders a genuine Icom or Motorola from the source, that it is real. Probably. But just randomly throwing gobs of money at a problem is a last resort which I'm very aware of, and have no desire to indulge in.

Surprising your analyzer behaves that way. Although I'm told that some use a third-order harmonic, etc. to test a frequency, and not the actual frequency they show, and that can cause some interesting misreadings.
 

ko6jw_2

Member
Premium Subscriber
Joined
May 18, 2008
Messages
1,128
Location
Santa Ynez, CA
Interesting theory. This analyzer does not radiate harmonics. Old RF generators used use harmonics to cover VHF or UHF, but that didn't mean that you couldn't use the signal just because it was a harmonic. In essence everything is a harmonic since digital synthesis starts with a fairly low clock frequency to begin with. The idea that an antenna analyzer set to 450Mhz is actually measuring the response of the antenna at 150Mhz is absurd.

I have a Diamond SHR320A 2 meter, 220, 440 antenna that tests just fine on all bands with this analyzer.
 

Rred

Member
Joined
Nov 21, 2014
Messages
830
"The idea that an antenna analyzer set to 450Mhz is actually measuring the response of the antenna at 150Mhz is absurd."
You are inferring a specific instance which I did not specify. According to a recent ARRL review, a particular (and well accepted) analyzer does in fact use third-order harmonics on the upper frequencies that it works with. I'm not mentioning names but you can find it if you look at recent ARRL reviews.
If you think the comments by the qualified staff at ARRL, who are quoting the manufacturer's own description of how their equipment works, are absurd, that's your opinion and you are welcome to it. Personally, I'll accept what they say, i.e. that this type of design can be problematic. Without knowing what equipment you are using, or how it actually is designed and working, all I can observe is that your results indicate that something you have is equally problematic.
 

zz0468

QRT
Banned
Joined
Feb 6, 2007
Messages
6,036
zz-
What are you suggesting? Check them at 144 and just presume whatever doesn't show a low SWR "must" be 440? That's kinda half the job, yes. Still doesn't tell me if the other half are really better suited for toasting marshmallows when there's no campfire.(G)
Yes, it's half the job. You indicated that you don't have a vswr meter that works to 440. So, without test gear, what exactly are your expectations? You have presented us with a problem to solve, but have no tools with which to solve it.

My only other suggestion is to attach the antennas to the radios and see if they perform adequately. If so, then the actual vswr doesn't matter. See my next post below.
 
Last edited:

zz0468

QRT
Banned
Joined
Feb 6, 2007
Messages
6,036
As an experiment I put various antennas on the top of the analyzer. The theory is that the analyzer was a simulated H/T. The results were disappointing.
I have an HP vector network analyzer that covers into the tens of GHz. In making calibrated measurements on things like portable radio antennas, some sort of counterpoise is required. How did you handle this for your measurements? With my instrument, I can see pretty flakey results too, unless I take a few extra steps. I find attaching the antenna to a solid ground plane gets me consistent repeatable results.

But that introduces cable length.

In making "real" measurements that have any meaning, one thing that needs to be established is the reference plane of the interface between the test equipment and the device under test (DUT). Otherwise, the line of demarcation between DUT and test gear is blurred- you don't know what parts of your measurements are DUT, and what are cable and test set. Some amateur grade instruments might have the unspecified reference plane at the rf connector. In others, it might be buried deep inside at the directional coupler that's used to sample the reflected energy for measurement. We usually just don't know.

So, one needs to try to be aware of how the instrument works, and then devise a test setup that works with it, not against it. That could be as simple as a set of critical length cables for each frequency band of interest. That's exactly what I do with my Bird 43 wattmeter.

Or, spend the money on an instrument that lets you calibrate the cables and fixtures out of the measurement.

Translating all of the above to layman's terms, measuring rubber duck antennas can be loaded with sources of error. Lacking tools and knowledge, just test them in radios and see what works and what doesn't. Forget swr, on an ht, it's going to be dependent on lots of external factors and the radio really doesn't care that much.
 

zz0468

QRT
Banned
Joined
Feb 6, 2007
Messages
6,036
Although I'm told that some use a third-order harmonic, etc. to test a frequency, and not the actual frequency they show, and that can cause some interesting misreadings.
Using a harmonic in itself isn't a problem, but it would be if enough of the fundamental frequency is leaking through. I'm not sure I understand how they could expect to make a meaningful measurement if the test frequency isn't known. Could you have misunderstood what the reviewers were saying?
 
Last edited:

Rred

Member
Joined
Nov 21, 2014
Messages
830
"So, without test gear, what exactly are your expectations?"
Begging, borrowing, or stealing the right gear, if necessary.
Testing radio performance while swapping out antennas and having a second person "over there" some distance to really compare how they are working was considered, but that's going to require a second person and a batch of time for both and still be somewhat objective.
I'm not surprised that no one really has any useful suggestions other than to say almost incidentally that ADDING A GROUND PLANE would make measurements way more likely to be real. A pie plate with an SMA0sized hole in it could do that. (Hell of a waste of a good pie plate though.(G)

On what the reviewers were saying? No, they were clear on that.
 

zz0468

QRT
Banned
Joined
Feb 6, 2007
Messages
6,036
"So, without test gear, what exactly are your expectations?"
Begging, borrowing, or stealing the right gear, if necessary.
Oh. Why didn't you say so?

So, getting back to your original question, is there a simple idea you're missing to test, the short direct answer is no.

Here's what you do:

1. Beg, borrow, or steal an Anritsu Site Master.
2. Install appropriate antenna connector on a suitable ground plane. No. A pie pan is not adequate for VHF. Use a quarter wavelength in all directions from center at the lowest frequency you plan to test on.
3. Calibrate test setup.
4. Measure antennas, and be aware that vswr alone won't determine how well the antenna performs.

Testing radio performance while swapping out antennas and having a second person "over there" some distance to really compare how they are working was considered, but that's going to require a second person and a batch of time for both and still be somewhat objective.
Well?

It sounds as if your trying to synthesize a batch of data without expenditure of any time or energy. The results of your testing will be commensurate with the effort you put into it.

Getting back to your original question again, no, there is no simple time and effort free way to test that you're missing. You will have to expend some effort to get the information you need.
 

Rred

Member
Joined
Nov 21, 2014
Messages
830
"Oh. Why didn't you say so?"
Maybe because I'm trying to focus on a solution, rather than philosophize about the universe in general?
Elsewhere, it seems that there are a number of inexpensive analyzers that will do the job, and be of use in the future.

"The results of your testing will be commensurate with the effort you put into it."
There's a difference between "easy" and "sloppy". That's why I was looking for an easy solution, not a sloppy one. Whether I need 0.5% accuracy or 5.0% accuracy, not your concern. Thanks for sticking to the original question, sorry that collateral concerns have kept you up all night.
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
14,647
Location
SNCZCA01DS0
So, a while back I had the same sort of question.
Test equipment availability wasn't an issue, setting up an accurate test was.

While mounting the portable antenna on a perfect ground plane will tell you a lot, it's also sort of fun to look at how the antenna actually works mounted on the radio.

So, having an old Kenwood TK-290 chassis available, I built this:



This lets me do a number of tests:
Test the antenna for resonance point.
Test for a damaged or intermittent antenna
Show the effects of how holding the radio impacts performance.
Test the "no name", Chinese and E-bay special antennas that people show up with at work.

I just removed the internals and soldered on a piece of a test cable I had. Might be an option for you if you've got an old HT laying around.
Or, you could probably fabricate something out of a metal project box that's about the right size.

Works pretty well.
 

Rred

Member
Joined
Nov 21, 2014
Messages
830
Using a dead h/t to totally (probably) match the hand/ground effects of the real thing. Very clever! Did you actually find the readings to be different from what you got with just the antenna, or the antenna with a little ground plane, by itself? (Other than being able to measure the body effects.)
 

prcguy

Member
Joined
Jun 30, 2006
Messages
10,511
Location
So Cal - Richardson, TX - Tewksbury, MA
To simulate an antenna on an HT you really need to decouple the coax from the radio frame to the test equipment, otherwise the long cable is part of the antenna system and will skew the measurements. A 6" long string of #43 mix ferrite beads is probably adequate or running the coax through both holes of a 43 mix binocular core is probably a little better.
prcguy

So, a while back I had the same sort of question.
Test equipment availability wasn't an issue, setting up an accurate test was.

While mounting the portable antenna on a perfect ground plane will tell you a lot, it's also sort of fun to look at how the antenna actually works mounted on the radio.

So, having an old Kenwood TK-290 chassis available, I built this:



This lets me do a number of tests:
Test the antenna for resonance point.
Test for a damaged or intermittent antenna
Show the effects of how holding the radio impacts performance.
Test the "no name", Chinese and E-bay special antennas that people show up with at work.

I just removed the internals and soldered on a piece of a test cable I had. Might be an option for you if you've got an old HT laying around.
Or, you could probably fabricate something out of a metal project box that's about the right size.

Works pretty well.
 
Status
Not open for further replies.
Top