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SWR for HT's


WRMN374
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I realize I'm gonna need an antenna analyzer for repeater setup. But for now I'm teaching myself with an Surecomm SW33 on my HT's. But I have a question. Would the SWR be higher on a factory antenna if the power is low? I'm in the process of making sure radios are fully charged before I check SWR and power output.

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On a low battery the HT power-output may be low (depending on the battery and the radio) but because SWR is a ratio of reflected power, it should not change significantly (if at all) based on power - especially when you are talking differences of only 1 or 2 watts.

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16 minutes ago, WRMN374 said:

But for now I'm teaching myself with an Surecomm SW33 on my HT's.

It is almost impossible to accurately measure SWR on an HT antenna.

An HT antenna is designed to work while attached to the HT, which is being held in your hand.  The radio and your body form the ground plane for the antenna.  If you detach the antenna and use jumpers to connect a meter and set the radio on the desk, you won't get accurate SWR readings.  So feel free to test out your meter to get familiar with it, but don't be shocked if you get really high readings.

Like @OffRoaderX said, SWR readings should NOT vary with power.  If they do, then your meter isn't very good.

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34 minutes ago, AdmiralCochrane said:

Would this be enhanced/corrected by using a real ground such as a "tiger tail"?

I’ve measured a number of my HT antennas. Originally I thought using a good ground plane would improve the match. Most didn’t, in fact some got worse. Since the human body ends up being part of the antenna system trying to qualify it for measurement purposes is difficult. In one test I did the best match was when the base of the small magnet mounted antenna was resting on the back of my hand held out at arm length. I was using a special small base magnet mount with an SMA connector on it for the tests. For a ground plane I used some sheet metal for heating duct work about 36 inches on a side to simulate a vehicle mount condition. All testing was done using a Rig Expert AA-1000 antenna analyzer.

https://rigexpert.net/index.php?route=product/product&product_id=57

Remember for GMRS a quarter wave antenna is about 6 inches long. An efficient antenna to match well is a half wave length long, in the case of GMRS that’s about 12 inches more or less. The metal case of the radio supplies the bulk of the missing half of the antenna, AKA ground plane. Adding a tigger tail likely won’t make much difference unless you have a tiny sized radio. Now if it was VHF there is some benefit seen when used.

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1 hour ago, AdmiralCochrane said:

Clarification: 

I wasn't refering to operation, but SWR  measurement.

That might be hard to measure, with or without the tigger tail. You would just about need to strip out the guts of the radio and run a pigtail out of it to the SWR meter. I haven’t seen how the manufacturers test their HT antennas but I would guess they do something similar.
 

I ran across a web site where someone built a simulated HT case with antenna connections on the top using a hollow block of aluminum. The test setup wasn’t that good since there was a noticeable length of open wire connecting the sockets together. At UHF that can really screw up the measurements.

This topic has come up before on the forum. If you can find some of my old posts some of them have links to web sites where people have attempted to measure HT antennas. If someone wants to give it a try I’m sure others would be interested in the results.

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41 minutes ago, Lscott said:

This topic has come up before on the forum. If you can find some of my old posts some of them have links to web sites where people have attempted to measure HT antennas. If someone wants to give it a try I’m sure others would be interested in the results.

a quick search found this one pretty fast:

 

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15 hours ago, wayoverthere said:

a quick search found this one pretty fast:

 

That looks like the one. The link for the simulated HT case for testing is at this link.

https://reflector.sota.org.uk/t/antenna-testing-jig-swr/14791

Looking closer you can see the "long" length of center conductor and shield braid going to each socket. This should have been kept as short as possible. Ideally he could have used one coax cable pigtail for each of the two sockets. There is a comment that the measured SWR's are "High" by 0.7 when verified against a dummy load, likely due to the above issue with the coax cable pigtail wiring.

Anyway testing HT antennas isn't going to be so straight forward or easy.

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