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Author Topic: VHF/UHF antenna solution for SUV  (Read 5901 times)
K9MAP
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Posts: 3




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« on: March 06, 2016, 11:04:36 AM »

*Also posted in mobile forum on QRZ, but wanted to also post here for non-QRZ users*
I'm in the market for a better antenna solution for my dual band radio in my Honda Pilot. I already have two NMO mounts installed in the roof and currently have one occupied with a Comet SSB-1 antenna. When I recently was diagnosing a transmit issue with my radio (Icom ID-880h), we saw that the SWR on 2 meters was around 2.0:1.
I already contacted Alan, K0BG, about option 2 and got his thoughts, but wanted to get some additional thoughts on two options I'm considering.

First, I live in the South/Southeast Denver suburbs. Most of the repeaters I talk on are located on mountain tops. Some are in the metro area.  I also prefer to park my Pilot in my garage and currently I have somewhere around 12-14" of open clearance.
My two options I'm considering are as follows:

Option 1: Larsen NMO 2/70B (open coil version) on the roof of my Pilot.  With this I'd have to get the optional Larsen spring and trim the antenna down accordingly. I've had the opportunity to test this antenna without the spring. I can get in and out of my garage ok, but going in the garage the open coil has a tendency to catch on the wood trim on the outside of the garage. I REALLY like this antenna but not sure if putting the optional spring on it would possibly degrade performance.  I also found I get noticeable "whistling" from this antenna when driving above 50MPH (I drive the interstate to and from work).

Option 2: Since I already have two NMO mounts, get two Larsen NMOQ 1/4 wave tunable antennas, trimming down one for 70cm and the other for 2m, getting the MFJ VHF/UHF diplexer (this is the only VHF/UHF diplexer I've been able to find), and have independent antennas for each band.  This would certainly provide best clearance but I'm afraid I might sacrifice some ability to hit repeaters that aren't on mountain tops.

At this point, I'm focused on getting Larsen antennas either way. I'm not really interested in the short comet/diamond antennas, nor am I interested in the longer antennas with the fold over features.

Thanks in advance for your comments and advice!
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K5LXP
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« Reply #1 on: March 06, 2016, 12:31:48 PM »

My two options I'm considering are as follows:

Option 1: Larsen NMO 2/70B
...
not sure if putting the optional spring on it would possibly degrade performance.

What does the Larsen documentation say?

Quote
I also found I get noticeable "whistling" from this antenna when driving above 50MPH

Heatshrink on the whip helps with that.

Quote
Option 2: ...get two Larsen NMOQ 1/4 wave tunable antennas,
...
I'm afraid I might sacrifice some ability to hit repeaters that aren't on mountain tops.

You don't have to guess, wonder or be afraid of anything.  They're just antennas.  In fact, with two mounts you could install two different antennas and do some direct A/B comparisons and not have to rely on any opinions of others.  Except for some pretty specific exceptions I predict you won't see a whit of difference between any of them.  I would even offer for you to try a 2M whip on 440 and see if that doesn't work well enough, and save you the trouble and expense of a diplexer.

Quote
I'm not really interested in the short comet/diamond antennas,

What if they worked as well as the quarter waves but saved you the cost of a diplexer?


Mark K5LXP
Albuquerque, NM

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K3GM
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Posts: 2547




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« Reply #2 on: March 06, 2016, 03:06:47 PM »

I have used Option #2 in the top of my Tahoe, and they worked great for repeater ops.  In my case I used a pair of Laird Technologies QWFT-120 They also looked very nice and we're great for low hanging branches in our heavily wooded area.
« Last Edit: March 06, 2016, 03:14:11 PM by K3GM » Logged
KT4NR
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Posts: 571




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« Reply #3 on: March 07, 2016, 06:29:56 AM »

I feel your pain.   Undecided  I run the NMO270 like you.

I've moved back to the land of parking garages. For some reason they are less than 8' tall usually (on my list of changes when I become supreme emperor of the universe.) I've done an install on my 4Runner on the engine hood. Its not because I want to, but, the wife is shorter and hence not likely to be able to pull over and yank an antenna from the center of the roof. Its a clamp type mount pinching on the hood. Its absolutely NOT ideal, but it'll do for now until I am struck with a better idea or elected supreme emperor LOL

Another option for you is get the other NMO270 which has a closed coil. Won't catch as bad.

Good luck.
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AI7PM
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Posts: 8




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« Reply #4 on: March 07, 2016, 08:38:21 AM »


Option 2: Since I already have two NMO mounts, get two Larsen NMOQ 1/4 wave tunable antennas, trimming down one for 70cm and the other for 2m, getting the MFJ VHF/UHF diplexer (this is the only VHF/UHF diplexer I've been able to find), and have independent antennas for each band.  This would certainly provide best clearance but I'm afraid I might sacrifice some ability to hit repeaters that aren't on mountain tops.

At this point, I'm focused on getting Larsen antennas either way. I'm not really interested in the short comet/diamond antennas, nor am I interested in the longer antennas with the fold over features.

Thanks in advance for your comments and advice!

I've used this option with gain and quarter waves. No noticeable difference with the diplexer inline.
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K6JH
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Posts: 511




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« Reply #5 on: March 07, 2016, 03:16:48 PM »

I've also done the 1/4 wave vs Larsen comparison, here in mountainous southern California. The 1/4 waves work fine - I was somewhat disappointed in the Larsen. In canyons I think the non-gain antennas are an advantage.

I've also run a short dual band Diamond NR72BNMO (13.8") when I only wanted one mount and needed clearance.
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73
Jim K6JH
KT4NR
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Posts: 571




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« Reply #6 on: March 08, 2016, 06:25:49 AM »

I've also done the 1/4 wave vs Larsen comparison, here in mountainous southern California. The 1/4 waves work fine - I was somewhat disappointed in the Larsen. In canyons I think the non-gain antennas are an advantage.

I've also run a short dual band Diamond NR72BNMO (13.8") when I only wanted one mount and needed clearance.

From my experience this has a lot of merit. I used to run one of the Japanese big gain antennas. I had a great signal getting into repeaters far away in the mountains but not getting into repeaters in the urban areas (even with remote receive sites.) Swapped to the Larsen NMO270 and no issues getting into the local repeaters, but at the cost of not having a good signal for far away machines. I believe the Larson NMO270 and the quarter wave have higher take off angles so you can work closer in. The super gain Japanese antennas must have a very low take off angle using the same mount on the same vehicle. That gives you the longer range and some more shadows locally.

I am willing to be wrong entirely here.
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N8EKT
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Posts: 687




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« Reply #7 on: March 08, 2016, 06:42:01 PM »

Yeah the Larsen NMO2/70 is the best dual bander bar none but it's a half wave on 2 meters and a colinear on 440 so very little of your signal will get to the mountain top repeaters

So looks like 1/4 waves on both bands is the only way to go

But I'd use commercial NMO "chrome dome" 1/4 waves by motorola, Laird, or Maxrad

They are much more flexible, cheaper, and the whip won't corrode like the Larsen whips usually do

« Last Edit: March 08, 2016, 06:52:19 PM by N8EKT » Logged
N3IDG
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Posts: 118




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« Reply #8 on: March 08, 2016, 06:52:33 PM »

I say option 3 put a 1/4 wave on an nmo for vhf and use as a 3/4 wave on uhf . Will work just fine with acceptble swr readings. And will flex just fine for your garage.
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N8DXB
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Posts: 15




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« Reply #9 on: April 17, 2016, 07:51:54 PM »

I ram a Larson NMO 2/70B in the roof of three trucks, and two Durangos (SUV) with great results.
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