Author Topic: HT Antennas' Performance & Questions  (Read 497 times)

Offline Greekman

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HT Antennas' Performance & Questions
« on: January 14, 2020, 05:09:01 AM »
hi all!

So i spent most of the morning on taking measurements of all my HT antennas with my SWR meter.

I got me a Baofeng UVF10 handheld that is triband (+220MHz) and of higher power.

I got a whole range of SWR measurements from 1.7 in V/UHF, out to 17 in the 220 band!!!

And it was a good chance to "evaluate" my anteenas.

So here come the questions:

1) Would you find a value of 2.5 in SWR acceptable?
Seems that an average of 2.2 is the norm regardless of antenna quality

2) The following i cannot grasp why it happens.
Depending on antenna, output power varied! most of the antennas would clock at 4-5W while I got 8 and 10.8 watts on some antennas.
i.e my base antenna would clock 5watts and 1.3 SWR, but a Nagoya Rh770 extendable would clock 10watt and lousy SWR in the 220 band.
(All V/UHFf measurements fell in the 5watt range)

Some how it seems that antennas at scored bad in SWR, were the ones that the meter showed higher output
Why is this so?
(I am assuming it was reflected power the meter was receiving on top of the TX generated one)

unfortunately i cannot post a table for the moment.

Funny notes.
The absolutely WORST antenna for the VHF was the stock Kenwood TH-F6 antenna!
Baofeng stock antennas are very good at the UHF (HAM & PMR bands)


Offline exSun

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Re: HT Antennas' Performance & Questions
« Reply #1 on: February 01, 2020, 05:28:50 PM »
How did you take the measurment? The chassis of the radio is part of the antenna (like a "ground plane").  And if you have any cable from the antenna connector sticking out of the chasis to go the the VNA, it's part of the ground plane too. Making measurments of isolated boxes like an HT is very tricky. In decades gone by, when I worked making such measurments on isolated boxes, the only thing allowed out of the box to connect to the instrumentation was a fiber optic cable. That would be a challenge even today.

Offline Greekman

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Re: HT Antennas' Performance & Questions
« Reply #2 on: February 02, 2020, 01:50:41 AM »
HT on hand, SWR meter screwed on the HT, Antenna screwed on the SWR meter.

SWR meter is a Red Dot, checked for accuracy
http://www.giga.co.za/ocart/index.php?route=product/product&product_id=238

Offline exSun

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Re: HT Antennas' Performance & Questions
« Reply #3 on: February 03, 2020, 12:35:00 PM »
It's nice they make the SWR meters so small and self contained now! Still, inserting it makes the antenna longer. This would most impact the highest frequency band readings.

The way the transmitters are designed, they roll back power when they see bad loads (usually - can't count on it though).

In any case, HT antennas are notoriously poor. In some cases, only the loss in the antenna makes the SWR "good." But usually they're good enough. If they aren't in a particular application, you can build a "jungle antenna" for the band in question, or make twin lead "j-pole" some of which work well on 2m and 3/4m.

Offline Greekman

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Re: HT Antennas' Performance & Questions
« Reply #4 on: February 04, 2020, 11:33:52 AM »
have already done a true jungle antenna and have bought me a slim jim..let alone the various flavors of 1/4 wave groundplanes I have built.

Funny thing is that during the measurements I measured more than 8 watts of output power out of the Baofeng with some bad antennas.
Huh????
well I suppose that it is reflected power down the SWr meter, down to the radio and back up again...


Offline exSun

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Re: HT Antennas' Performance & Questions
« Reply #5 on: February 06, 2020, 09:52:58 AM »
well I suppose that it is reflected power down the SWr meter, down to the radio and back up again...

That is exactly right! The power produced by the radio is the forward power minus the reflected power.

Long ago my employer used a similar trick and nearly lost a contract due to the disbelief of a gov't.  inspector. We had a device called a "circulator" (at HF - quite the trick) and used it to test a pair of back to back 50kW baluns. The transmitter powering the test was a 10 kW TX. The inspector called BS. But the circulator took the power coming out of the baluns and added it into the power coming from the TX. Inline power meters on either side of the baluns confirmed 50 kW. The TX only had to make up losses. Ultimately the inspector was convinced and the product approved.