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Dual band NGP antenna for off-road use

Joined
Oct 31, 2018
Messages
16
#1
I'm looking for a suitable antenna for my Jeep, which I use almost exclusively off road. The need is a no ground plane dual band antenna that's capable of transmitting across all 2M, 70cm, and GMRS frequencies. I'll spend most of the time on the 70cm and GMRS frequencies, so 440-470 MHz. Ideally, I'd like an antenna no longer than 36", but if it's a little longer, that's no deal breaker.

Please let me know what's available, as I've searched and searched and found nothing suitable for my needs. Again, being no ground plane is a major qualifier as well as capability to transmit up to 470+ MHz.

Thanks!
 
Joined
Jul 27, 2005
Messages
10,047
Location
Point Nemo.
#5
Finding good half wave DUAL BAND antennas can be an issue.
Can you do two separate antennas? Add a diplexer and you've got some more choices.

I've got a Laird half wave VHF antenna that I use on a Polaris Ranger. I've got it mounted on the back of the roll cage. Works well. I've smacked it on tree branches while running down trails at 30-35mph, and no issues, other than a slight bend at the very top of the whip.

Add a half wave UHF and you'll probably be able to cover 70cm and GMRS if you tune it for somewhere around 455mHz.

For off road use, I'd recommend antennas with a spring in the base. It can help absorb some of the hits.
 

ladn

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Joined
Oct 25, 2008
Messages
272
Location
Southern California
#8
Larsen 2/70. Best quality, most durable. For the bandwidth you're looking for, dual band is going to be a compromise. Expect 2:1 VSWR or higher on GMRS.
I'll second that. The 2/70 is an excellent antenna. I use mine for 2m, MURS, 70cm and GMRS (plus vhf/uhf monitoring). If you can, order the antenna in two parts (the coil base and the whip). Look for the old style whip with the solid loading coil. The newer version has an open air coil. The RF performance is the same, but the open air coil is a branch catcher.
 
Joined
Jul 27, 2005
Messages
10,047
Location
Point Nemo.
#9
Issue is finding a dual band no-ground plane antenna. While the Larsen 2/70 is a nice antenna, it's not a no ground plane on VHF -and- UHF.
 

AI7PM

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Sep 6, 2015
Messages
393
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The Intermountain West
#10
Issue is finding a dual band no-ground plane antenna. While the Larsen 2/70 is a nice antenna, it's not a no ground plane on VHF -and- UHF.
Interesting in that, the dual band antennas I've used that were 1/2 wave VHF, were colinear 5/8 over 5/8 on UHF, and usually gave me around a 1.5:1 VSWR on UHF over a compromised or no ground plane. Something going on there above my knowledge base. Thoughts?
 
Joined
Jul 27, 2005
Messages
10,047
Location
Point Nemo.
#11
I suspect the lack of ground plane isn't problematic enough to be an issue. But I'd like to see what the radiation pattern looks like.

I ran the short version (NMO-2/70sh) for a few years. It was 1/4 wave on VHF and 3/4 wave on UHF, which is the same as just running a standard 1/4 wave VHF whip. 3/4 wave on UHF gives a bit of a funny radiation pattern compared to a 1/4 wave.
I moved away from dual band antennas and switched to separate VHF and UHF when I had both in my vehicle. Gave me more options and control. I preferred the lower profile of 1/4 wave antennas on the roof of a full size truck anyway.
 
Joined
Jul 27, 2005
Messages
10,047
Location
Point Nemo.
#13
For receiving? It'll work OK. I believe they are 1/2 wave on VHF, and half wave tend to be a bit broadbanded. So while 151-155 might not be in the "sweet spot" the antenna is tuned for, it's probably going to work OK.

For transmitting, you'd want to confirm reflected power would be low enough to not cause other issues.
 

mancow

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Database Admin
Joined
Feb 19, 2003
Messages
5,807
Location
N.E. Kansas
#15
For receiving? It'll work OK. I believe they are 1/2 wave on VHF, and half wave tend to be a bit broadbanded. So while 151-155 might not be in the "sweet spot" the antenna is tuned for, it's probably going to work OK.

For transmitting, you'd want to confirm reflected power would be low enough to not cause other issues.
So being half wave they would be OK on a small or non ground plane mount like a jeep?
 
Joined
Dec 19, 2002
Messages
903
#18
My understanding has always been the NMO270 was 1/2 wave on 2M so it should work without a groundplane. Larsen literature has stated in the past that 1/2 wave antennas work without a groundplane but work better with one.
 
Joined
Oct 31, 2018
Messages
16
#20
Bought the Larsen 02/70B and it doesn't work as well as the $14 Tram 1181 I had on there. They both yield 1.0 - 1.2 on VHF, but the Larsen is around 1.6 - 2.3 on UHF until you get above 450 MHz. It's a perfect 1.00 at 455 MHZ, but that's above the frequencies all the repeaters are on. Granted, it IS better on FRS/GMRS than the Tram, but it's still around a 2.7 - 2.9 on GMRS. The Tram is 7.8 - 8.3 on GMRS. Both are around 2.2 on MURS.

Needless to say, the Tram is back on and the Larsen is going back.
 
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