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Author Topic: How do i messure if my hand-held radio's antenna is in resonance?  (Read 3080 times)
LB5KE
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Posts: 141




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« on: November 16, 2013, 12:35:32 AM »

I have several antennas for my Yaesu and Baofeng radios. So far i have usually just compared the antennas between each other and presumed it has low SWR if it works OK.
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K6LCS
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« Reply #1 on: November 16, 2013, 08:50:29 AM »

Measuring anything about an HT antenna is a waste of time (grin) ... Just know that the stock ducks are about NEGATIVE 2 or NEGATIVE 3db (if not worse). No other 7-8" antenna is going to perform better. A 17" whip will dramatically improve comms. And with 2M and 440 on an HT - it is all line of sight.

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Clint Bradford, K6LCS
http://www.work-sat.com
KA4POL
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Posts: 2086




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« Reply #2 on: November 16, 2013, 11:26:36 AM »

To answer your question, the serious method is using a network analyzer like this one: http://sdr-kits.net/VNWA3_Description.html
Of course there are also commercial ones at much higher cost.
However, you could use a regular SWR meter for 2 m and 70 cm and check out the values your antennas produce. This is a much cheaper way but also not as accurate.
I know that the Baofeng UV-5R stock antenna is so bad, it gets warm after just some minutes of transmitting. That clearly is a sign of a terribly bad antenna.
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WB6BYU
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Posts: 13458




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« Reply #3 on: November 16, 2013, 11:37:59 AM »

That is actually a very difficult measurement to make,  because half of the antenna is the
case of the radio, and anything you add in line to make a measurement will affect the
combination of the two.

One of the companies that builds rubber duck antennas used to show off their test fixture:
basically a primitive SWR analyzer (before such things were available for most hams) in
a case about the same size as an HT.  This allowed them to tune them for a good match
with roughly the same "other half of the antenna" as one would encounter with an HT.

With today's smaller HTs it is even more difficult.

If you just want to check the antenna, you can put a matching fitting in the middle of a
metal sheet, mount the antenna on that, and run coax from the back side to an SWR
meter or antenna analyzer.  In some cases you may be able to plug the antenna
directly into an analyzer, on the assumption that it is roughly equivalent to an HT.
But that might take a couple of adaptors to get the plugs to match.

A more primitive method is to monitor the signal strength as you bring your hand
towards the antenna (perpendicular to the direction of the signal.)  If the signal
strength goes up, it may indicate that your antenna is tuned too high, and the
added capacitance to your hand is bringing it more into resonance.  However
there are a number of potential sources of error with this method.


The most practical method I've found for testing antennas is to try several on
the same HT while monitoring the signal strength.  (A diode detector, possibly
following a tuned preamp, driving a digital voltmeter may give you sufficient
precision to at least say which one is better.)  That way I know which antenna
works best with that particular radio, whether they are resonant or not.  You
can also do this by monitoring a distant repeater or other signal source, especially
if your radio has a useful S-meter (not all of them do.) 
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LB5KE
Member

Posts: 141




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« Reply #4 on: November 17, 2013, 03:23:51 AM »

I know that the Baofeng UV-5R stock antenna is so bad, it gets warm after just some minutes of transmitting. That clearly is a sign of a terribly bad antenna.

The stock antenna is OK on UHF, but i did get a good improvement on VHF Using a Nagoya NA-771SF, bought on ebay. I guess there are even better antennas out there.
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