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Diamond SG-7900-A-NMO on GMRS Frequencies?


Best Answer WRCR8872 , 18 March 2019 - 05:46 AM

Check out these two Comet antennas, CA-2x4SR & CA-2x4SRNMO.

 

1.5:1 or less SWR:

144-148/440-450MHz
2:1 or less  SWR:
140-160/435-465MHz
Gain: 3.8/6.2dBi

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#1 marcspaz

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Posted 16 March 2019 - 09:40 PM

I am wondering if anyone has used a Diamond SG-7900-A-NMO on their vehicle, on GMRS frequencies?  If so, how did it go?

 

I am looking at getting a better mobile antenna.  A radio I just ordered covers 2 meter, 70 cm and GMRS frequencies.  I am thinking about getting a Diamond SG-7900-A-NMO for 2m/70cm use.  I had one before and it worked great for its intended use.

 

The antenna is pre-tuned and not adjustable.  The Ham UHF frequencies stop at 450 MHz.  I am hoping the antenna will be tuned close enough to get good performance and have a good SWR on GMRS frequencies as well.  It will make life easier if I don't have to swap antenna's as I move between Ham and GMRS.

 

Any feedback on your experience on this is much appreciated.

 

Thanks,

Marc



#2 Corey

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Posted 17 March 2019 - 11:35 AM

I have not had or seen anybody have good luck running a dual band ham antenna on GMRS, In my personal experience the trusty NMO UHF 1/4 wave has given me the best performance for repeaters and hwy simplex use and most will cover 440 to 480. No issue with repeaters 30 miles away and regularly see 10 miles simplex on the hwy. 


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Just My $.02

 

Corey

 

Midwest GMRS

https://mwgmrs.com


#3 marcspaz

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Posted 17 March 2019 - 11:55 PM

That's good to know. If that's the case, I'll likely keep both antennas in the truck and just swap them as needed.

I appreciate the reply.

#4 WRAF213

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Posted 18 March 2019 - 03:14 AM

There's a 1/4 wave dual-band whip on my car, even that simple construction cuts off right at 450 MHz. Most of those dual band antennas are based on 70cm being around the third harmonic of 2m, and 467 MHz is quite some distance from the third harmonic of 148 MHz.

Most of those multi-band ham antennas are designed to give good SWR inside 144-148 and 440-450, and SWR will rise very quickly above 450 MHz. As a good rule of thumb, higher gain antennas are narrower-bandwidth than lower gain antennas.
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#5 WRCR8872

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Posted 18 March 2019 - 05:46 AM   Best Answer

Check out these two Comet antennas, CA-2x4SR & CA-2x4SRNMO.

 

1.5:1 or less SWR:

144-148/440-450MHz
2:1 or less  SWR:
140-160/435-465MHz
Gain: 3.8/6.2dBi


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#6 marcspaz

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Posted 21 March 2019 - 09:41 PM

I just wanted to take a moment to follow-up on my research and testing.  Just so everyone knows there is no bias, I do not work for, nor have any connections to Comet or any other two-way radio communications companies.  This is a totally unbiased opinion.

 

I actually found a great, multipurpose antenna (Thanks KD2NCN / WRCR872 !).  I bought a Comet CA-2x4SR NMO and its performance exceeds my expectations.  Comet advertises this antenna for this very purpose and they did not let me down.

 

My dedicated GMRS antenna (Midland MXTA11) had a 3:1 SWR on channels 1 through 7 (shared FRS/GMRS) and 15 through 22 (GMRS only).  On the FRS channels it had a SWR of 2.5:1.  Likely due to the extremely low power of the handheld, otherwise it would have be 3:1, too.  On the 70cm frequencies, that antenna actually did very well, with a 1.5:1 SWR.  On 2 meter, it was over 5:1. 

 

The Comet antenna has a 1:1 SWR on 2 meter, 1.2:1 on 70cm, and a 1.5:1 on all FRS and GMRS frequencies.  In my simplex testing on channel 15, while using the old antenna, my mobile to mobile between my two trucks was a max of about 2.6 miles in the suburbs.  The new max is 8.3 miles in the same suburbs.  Also, I got a signal report that I was "full quiet with loud audio" on a repeater that was 28 miles from my test location, while using a full 50 watts.

 

If there are any Hams looking for a good 2m/440/FRS/GMRS antenna, I highly recommend this one.

 

Hope this helps someone.

Spaz



#7 WRAF213

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Posted 24 March 2019 - 01:40 PM

Just remember that while simplex operation happens down at 462 MHz, duplex operation transmits at 467 MHz and SWR / return loss should be checked at 467 too.


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