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tuning handheld antenna..


cbrown038
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I have a couple Btech V1's and am trying to tune the Nagoya 771.  As i trim the length, the SWR is dropping little at a time, (1.05) but when I move a substantial distance (4 miles ish) the swr changes (2.5). 

 

Im new to gmrs and radio's in general, but how can I get an accurate swr when it is changing seemingly constantly?  I must be doing something wrong. I do not want to trim it to short and have to buy another one..

 

any help or suggestions would be appreciated

 

WRKI386

 

 

Im using the SW-33 swr

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You cannot measure SWR of HT antenna by simply attaching the meter between HT and antenna. The body of HT coupled with your body is a part of antenna. You need measuring apparatus inside the HT to have a meaningful measurements. Attempts to use regular SWR meter to measure SWR of HT antenna are futile. SWR numbers measured this way are meaningless and junk science (junk engineering).

 

And on top of that, SW-33 is not to be trusted on UHF, according to my personal experience.

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The Nagoya 771 is a dual band amateur band antenna...which judging by its length, looks like a 1/4 wave on 2 meters and 5/8 wave on 70 cm ham band.  I personally would not use this antenna for GMRS.  This antenna would need to see some sort of ground plane to radiate properly, in addition to properly loading for lowest reflected power.  As i am a Motorola person, I am not certain about the construction of the Btech radio in regards to the case acting as a proper ground plane.  If it does not have a metal chassis, or metal impregnated case, and is only relying on the SMA connector for a ground plane, I am not so certain that your goal of antenna trimming will ever be achieved reliably.

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The Nagoya 771 is a dual band amateur band antenna...which judging by its length, looks like a 1/4 wave on 2 meters and 5/8 wave on 70 cm ham band. I personally would not use this antenna for GMRS. This antenna would need to see some sort of ground plane to radiate properly, in addition to properly loading for lowest reflected power. As i am a Motorola person, I am not certain about the construction of the Btech radio in regards to the case acting as a proper ground plane. If it does not have a metal chassis, or metal impregnated case, and is only relying on the SMA connector for a ground plane, I am not so certain that your goal of antenna trimming will ever be achieved reliably.

Nagoya also makes a 771 version for GMRS, model is ‘NA-771G’. I own two of them.

 

 

Michael

WRHS965

KE8PLM

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As others have pointed out trying to measure the SWR of the type of antenna that mounts on a hand held radio is difficult at best. I’ve personally have tried nearly a dozen different types. Changing the test setup resulted in wide variations in the measure SWR. In the end about the only thing I could reasonably conclude is antenna “x” seemed better than antenna “y” under the same conditions, which may not translate in to how the radio sees it when installed.

 

I know some of the commercial radios I have use “hybrid power modules” for the output stage. I looked at the data-sheet for a few and saw they were specified to work with an SWR up to 20:1 for one model if I remember right. You could key the radio up briefly with no antenna and likely not blow out the power stage!

 

Hand held radios have to work in many different environments, in your hand speaking into the mic, hanging on a belt with the antenna basically against the body etc. All of which drastically changes the SWR and the radio has to work. If you get a name brand antenna, yeah there are counterfeits mainly from China, I wouldn’t worry too much about it.

 

The only test that has any real validity when measuring hand held radio antennas is the field strength. Some antennas are very inefficient wasting most of the power from the transmitter. Some of the frequently called “rubber duck” antennas, the short semi-flexible rubber coated ones, have been measure with as much as a negative 5db gain, which translates in to roughly 2/3 of you transmitter power wasted in the antenna. That’s why most people look for a “better” antenna for their radio.

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Seems to work pretty well on the video linked below..  

 

Obviously, I can't give full credibility to anybody as I actually don't know anybody..

 

 

Start watching at about 9:00 mark on the video.. and let me know what you think i guess.  

 

https://youtu.be/OTWvLuEuYXU

Mine SW-33 is a lemon for sure. The video demonstrates 3 power measurements (at 4.3W) that are consistent. Mine never gives consistent results when doing several measurements on UHF.

However, I will stand with what I said before about SWR measurements shown in the video: meaningless. Especially on GMRS frequency, where inserting SW-33 lengthens the antenna (actually half of the antenna, check the article posted by Lscott) by roughly 1/8 wavelength.

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Seems to work pretty well on the video linked below..  

 

Obviously, I can't give full credibility to anybody as I actually don't know anybody..

 

 

Start watching at about 9:00 mark on the video.. and let me know what you think i guess.  

 

https://youtu.be/OTWvLuEuYXU

 

The guy from NotARubicon put out a newer video where he includes what he learned about SWR measurement and HTs.  Not sure even the bracket method would suffice.  Maybe recording the readings to video while using/holding the HT the "right" way and reading the numbers from the video would be best?

 

https://youtu.be/p9O_l4BO8hc

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BUYTWOWAY Radio has a Nagoya NA 771G  Says it's tuned For GMRS But they are sold out of course and I cannot Find them anywhere else.   I did notice they sell them with a Bundled set of GMRS radios.  Anyone ever use that Antenna?  I think they come in 1/4 nd 1/2 wave.  Can't find them and No businesses actually use a phone now. Just internet.  OUT OF STOCK.   

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BUYTWOWAY Radio has a Nagoya NA 771G  Says it's tuned For GMRS But they are sold out of course and I cannot Find them anywhere else.   I did notice they sell them with a Bundled set of GMRS radios.  Anyone ever use that Antenna?  I think they come in 1/4 nd 1/2 wave.  Can't find them and No businesses actually use a phone now. Just internet.  OUT OF STOCK.   

 

They sale out as ppl buy them. I got a 771G about a month ago.

BTWR is in a partnership for the design/tuning of the 701G and 771G, so they are the only place to buy one.

 

The next closest antenna is the 701C, tuned to commercial range UHF (450-470MHz).

https://www.amazon.com/Nagoya-NA-701C-Commercial-SMA-Female-BTECH/dp/B01AX3AYOK/ref=sr_1_1?dchild=1&keywords=701c&qid=1612466961&sr=8-1

I have been using the 701C and wanted a bit more range with the longer 771G.

 

 

73

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