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Commercial Radio Antennas - Please keep discussion related to professional, commercially used antennas and antenna systems for the two-way radio industry. Topics for the use of these antennas on amateur bands are accepted here.

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Old 05-13-2017, 12:56 AM
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Default Dual Band mobile antenna question?

Hello, is it possible to tune the vhf portion of an antenna for 2 meters and the uhf for commercial frequencies. I suspect that the 70cm radiator could be shortened to achieve the higher frequency needed for the commercial frequencies. Not sure if this would affect the 2 meter side. I would like to only use one antenna for both bands as I only use 2 meters for ham use and uhf for commercial use. A concern would be the third harmonic of 144 MHz which is 432 MHz but I will be in the 464/469 MHz range. Thank you for any info provided. mpsabre
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Old 05-13-2017, 7:17 AM
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What model antenna is it? What do the instructions say?
It's not possible to do that to any of the dual band antennas I have ever used because the whole whip is active on both bands.
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Old 05-13-2017, 7:17 AM
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Larsen makes that antenna in ham and commercial both look up the specs the rods can be cut but the coil may different.
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Old 05-13-2017, 8:56 AM
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But you still have to choose between ham VHF and UHF or commercial VHF and UHF. You can't mix and match--ham VHF and commercial UHF--with a single whip. The UHF resonant frequency is 3x the VHF resonant frequency.

The only way to do this is to have separate antennas and a duplexer, or else an antenna with multiple radiating elements like a LPDA or ST-2.
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Old 05-13-2017, 9:55 AM
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Just get one of these: http://www.cometantenna.com/wp-conte...9/CA-2x4SR.pdf
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Old 05-13-2017, 10:00 AM
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I have a Comet CA-2X4SR. It's supposedly designed for what you're describing. I haven't used it yet as I just got it.
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Old 05-13-2017, 12:45 PM
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Sacrifice some antenna gain and go with a dual band antenna built off the 1/4 wave design on the VHF side. Larsen used to sell a "short" dual band antenna, NMO-270SH that would work well. Lower gain antennas usually have wider useable bandwidth.

One option you could try is a simple 1/4 wave VHF antenna. It'll work as a 3/4 wave on UHF. I used one for years with a dual band amateur radio. SWR was 1.3:1 on 2 meters and 1.1:1 on 70cm. The trade off is the radiation angles on UHF are a bit funky, but I never had an issue with it. You can pick up a 1/4 wave VHF antenna for about $10 and give it a try.
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Old 05-13-2017, 7:51 PM
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Quote:
Originally Posted by prcguy View Post
You HAVE to be joking, terrible junk thing should not even be called an 'antenna'.
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Old 05-13-2017, 8:32 PM
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Comet CA-2x4SR Product Reviews

Check the eham review. Doesn't look like junk to the reviewers, and the rating is one of the highest of any product on eham.
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Old 05-13-2017, 9:00 PM
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Quote:
Originally Posted by jaspence View Post
Comet CA-2x4SR Product Reviews

Check the eham review. Doesn't look like junk to the reviewers, and the rating is one of the highest of any product on eham.


The comet ca-2x4sr…antenna with a history. Comet originally sold this as a search and rescue antenna. I purchased two of them (one for a roof mount on my dd at the time and anther for my XJ on a tire carrier mount). While the one on the XJ held up surprisingly well, the one on my dd did not. Ended up striking a tree branch (~halfway up the antenna) and that was the source of all my problems. Many have stated, it'll fold over if you strike something…don't count on it. Mine ended up pulling the NMO mount out of the roof of my vehicle. Luckily the tabs on the mount failed and the sheet metal didn't tear (note, I did not say there wasn't sheet metal damage, I was just able to fix it with a DBH).

Now a causal observer might say, there is a spring that you could've used. Well, it was t released with the antenna and when I found this major drawback to the antenna…it still hadn't been released. After fixing the roof, ghat antenna literally got trashed on principal and replaced with a Sti-Co Flexiwhip. Never noticed a performance difference…since I had an unused mount which got a PCTEL wideband knob for UHF (430-480 MHz).

Now if dual antennas aren't an option some of the multi band commercial antennas will get you pretty close. For example, my current DD has a Panorama Sharkee with Panorama's "trident" (tri-band) whip. It's rated at 146-174/430-480/764-896 MHz under a 2.0:1 SWR. However, it covers the rest of 2m with an SWR under 2.5:1 and for using they portion of the band once every other year…it's fine.


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Old 05-13-2017, 9:35 PM
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Are you speaking from first hand experience? If so fill us in because I was about to order one to play with.
prcguy

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Originally Posted by cmdrwill View Post
You HAVE to be joking, terrible junk thing should not even be called an 'antenna'.
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Old 05-13-2017, 10:28 PM
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Quote:
Originally Posted by prcguy View Post
Are you speaking from first hand experience? If so fill us in because I was about to order one to play with.
prcguy

YES, junk. Save your money. I would sell it but it really belongs to the county... paperwork.

A quarter wave antenna replaced it and no more complaints about "they can not hear us".
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Old 05-15-2017, 1:20 PM
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Thank you all for your input. I have decided to use two separate dual band antennas with a coax switch as this appears to be the best solution. Thanks again, mpsabre.
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Old 06-05-2017, 6:37 PM
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A typical high band vhf 1/4 wave (18 inches) will work as a dual band antenna with somewhat poor performance on UHF but the swr will be fine
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Old 06-05-2017, 7:46 PM
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Hello , I have been useing a Comet CA-2x4SRNMO for several years and I really like the antenna.
Best duel band mobil I have used ever used.
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