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Author Topic: Measuring VSWR VHF/UHF  (Read 4376 times)
K2OWK
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Posts: 1066




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« on: November 09, 2010, 01:15:06 PM »

I was wondering if there is any way to measure VSWR on a HT VHF/UHF radio without using a VSWR meter? I would hate to spend $50 or $75 on a meter I would only use once or twice.

Thanks,
73s
K2OWK
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WB2WIK
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Posts: 20614




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« Reply #1 on: November 09, 2010, 03:25:47 PM »

I was wondering if there is any way to measure VSWR on a HT VHF/UHF radio without using a VSWR meter? I would hate to spend $50 or $75 on a meter I would only use once or twice.

Thanks,
73s
K2OWK

You don't measure VSWR on a radio, you measure it on the antenna, no matter what the radio is.

What kind of antenna did you have in mind that you want to measure?
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K2OWK
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Posts: 1066




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« Reply #2 on: November 09, 2010, 04:07:22 PM »

I want to measure a mobile 2 meter/70 centimeter antenna. It is a Laird that I picked up at a Ham fest for a low price with the magnetic mount. It works well on receive. I have not tried to transmitt with it yet. The fellow I bought from said it was a dual band, but I am not so sure about it. It is a single wire measuring 19" with no center coil. I want to check the VSWR on 2 meters and 70 centermeters to make sure it is resonant on both frequency's not just on 2 meters that the length is set at.

73s
K2OWK
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WB2WIK
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« Reply #3 on: November 10, 2010, 08:54:20 AM »

I want to measure a mobile 2 meter/70 centimeter antenna. It is a Laird that I picked up at a Ham fest for a low price with the magnetic mount. It works well on receive. I have not tried to transmitt with it yet. The fellow I bought from said it was a dual band, but I am not so sure about it. It is a single wire measuring 19" with no center coil. I want to check the VSWR on 2 meters and 70 centermeters to make sure it is resonant on both frequency's not just on 2 meters that the length is set at.

73s
K2OWK

The dual band antenna does have a center "coil" as you suggest; if your 19" whip does not have this, I really doubt it's a dual-band antenna.

A 1/4-wave 2m whip will "load up" on 70cm (third harmonic) since all 1/4-wave unipoles, like 1/2-wave dipoles, will do this.  But if it's just a straight 19" wire, it will be a lousy 70cm antenna, even if it has a perfect SWR.
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WB6BYU
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Posts: 13355




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« Reply #4 on: November 10, 2010, 09:03:20 AM »

Quote from: WB2WIK
But if it's just a straight 19" wire, it will be a lousy 70cm antenna, even if it has a perfect SWR.


Well, "lousy" depends on what you expect from it.  Not as good as one designed for dual band
use perhaps, but I recently used a straight 2m whip on 440 for a while and  it hit the 440 repeaters
just fine.  The antenna isn't optimum on 440, but due to the terrain I commute through the
440 repeater is either local or hidden behind some hills, and in that situation the 2m whip works
as well as anything else.  In a flat area the dual band version will allow you to hit the repeater
from a longer distance.

So if your concern is simply hitting a local repeater, the straight 2m whip should be usable.  In
marginal conditions you'll have better results with one designed for dual band use.  But you won't
be able to tell the difference with an SWR meter, since both designs will have a relatively low
SWR on 440.  The difference is in the vertical angle of radiation.

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K2OWK
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Posts: 1066




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« Reply #5 on: November 10, 2010, 12:52:43 PM »

Thanks everyone, I appreciate all the information. I am going on a trip shortly, and will let you know how the antenna works out on both frequency's.
Regards,
73s
K2OWK
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W7AIT
Member

Posts: 489




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« Reply #6 on: November 10, 2010, 02:06:01 PM »

No one answered your question.

I use either a Diamond SX-600, Diamond SX-1100 for quick VHF, UHF, Microwave SWR measurements.

For very accurate SWR measurements, I use my INSTEC GSP830 Spectrum analyzer with tracking generator and  Minicircuits or HP directional couplers to measure return loss, which I then convert to SWR.  This method is by far the more accurate and complete method as the data is continuous swept measurement between F star and F stop so I can see any "holes" or other anomalies.

Most hams probably just use the Diamond meters and that's usually good enough.  The SX1100 goes to 1300 MHz. 
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K2OWK
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Posts: 1066




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« Reply #7 on: November 10, 2010, 09:59:36 PM »

 Thanks  again for the information. I do not have access to a spectrum analyzer nor can I afford to buy one. I see some VHF/UHF Power meters and VSWR measuring instruments on EBay at about $50.00. I may purchase one of these and be done with it. I do have access to a Grid Dip Meter. I have the 100 to 500 MHZ coils. I am just curious if it is possible to check the antenna resonance with this meter? Just a thought.

Regards,
73s
K2OWK
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KI4QPU
Member

Posts: 59




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« Reply #8 on: November 12, 2010, 10:37:18 AM »

My suggestion would be to ask a neighboring ham if you could check the antenna with one of their meters/ analyzers. Plus you get to meet another ham. All that would cost you is gas to their house. Or maybe he or she could bring it to a club meeting.
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K2OWK
Member

Posts: 1066




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« Reply #9 on: November 12, 2010, 12:51:36 PM »

Thanks, I belong to the Tupelo Armature Radio Club. I will check at the next club meeting to see if anyone has a meter I can borrow. I am a new member of the club. The club itself may have a meter I can use. They have a lot of radio equipment in the club house.

Regards,

73s

K2OWK
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