NMO2/70SH vs NMO2/70B

[PrivatelyJeff]

I recall reading somewhere that the whip with the open coil is prone to whistling on the highway. Don't know this to be true since I've never used one.

It’s a “your mileage may very” thing. I had a window mount open coil antenna on the back window of my car that did that very loudly but the one on my roof doesn’t. I’m thinking since it’s longer with a spring, it’s able to flex just enough to mitigate any airflow movement that would cause a whistle.

I’ve also heard that if it does whistle, just putting a piece of heat shrink tubing around the coil stops it.

 

[mmckenna]

I recall reading somewhere that the whip with the open coil is prone to whistling on the highway. Don't know this to be true since I've never used one.

They do. My brother in law ran one for years. It whistled loudly at highway speeds. I gave him my old NMO-2/70SH and he was much happier, specifically said "no more whistle".

The heat shrink over the open coil can help quite a bit, but won't always fix all of it. I live near the ocean and fog is common. When cresting the mountain pass heading west, even my 1/4 wave VHF whip would start to whistle in the damp air.
I also noticed that a dirty whip will add to it. Wiping the whip down with a wet cloth and taking off the layer of dead bug guts and dust helped a bit.

 

[Firekite]

I recall reading somewhere that the whip with the open coil is prone to whistling on the highway. Don't know this to be true since I've never used one.

Silly question maybe, but is there any reason you couldn’t slide a section of heat shrink tubing over that open coil to make air have to go around it instead?

EDIT: That’s what I get for not realizing there was another page of replies!

I’ve also heard that if it does whistle, just putting a piece of heat shrink tubing around the coil stops it.

The heat shrink over the open coil can help quite a bit, but won't always fix all of it.

 

[mrweather]

I've been fortunate in that my trunk-mounted open coil NMO2/70B doesn't whistle. Guess it comes down to aerodynamics and how the air flows over the roof and down the back.

I've had more whistling from roof-mounted antennas.

 

[mmckenna]

I've had more whistling from roof-mounted antennas.

Yeah, my brother in law had his NMO-2/70b mounted dead center on the roof of a full size pickup. Switching to the NMO-2/70sh fixed it.
My 1/4 wave that whistles when it's foggy is also mounted dead center of a full size pickup roof, so they are absolutely out there front and center in the wind.

 

[tweiss3]

Yeah, my brother in law had his NMO-2/70b mounted dead center on the roof of a full size pickup. Switching to the NMO-2/70sh fixed it.
My 1/4 wave that whistles when it's foggy is also mounted dead center of a full size pickup roof, so they are absolutely out there front and center in the wind.

This is a good point. This setup is scheduled to transfer over to a new silverado this year from my equinox. I say scheduled because along with other things, it completely depends on availability (have you seen car lots lately). Besides the noise, the Silverado's are taller, so I will hold off for now.

I also don't see the closed version available anywhere. It doesn't appear in the Larsen catalog. I see the SH, the B and the C is the commercial cut for 150MHz.

 

[mmckenna]

This is a good point. This setup is scheduled to transfer over to a new silverado this year from my equinox. I say scheduled because along with other things, it completely depends on availability (have you seen car lots lately). Besides the noise, the Silverado's are taller, so I will hold off for now.

Yeah, I have a friend who's the sales manager at a large Chevy dealer. They've been short on trucks due to chip shortages. Some of the ones they have been able to get have some of the features deactivated until they can get caught up.
I was down there this weekend turning in my dad's 2019 Silverado since my mom didn't need it, and they were very happy to have a good used, low milage one on the lot. She got a lot of money for that truck as they can easily sell it way above bluebook price.

I also don't see the closed version available anywhere. It doesn't appear in the Larsen catalog. I see the SH, the B and the C is the commercial cut for 150MHz.

The closed coil version of the NMO-2/70 has been gone for quite a while. The last one I had was purchased back in 1990 or so. The SH is still available. There used to be an open coil version of the SH, I have it running connected to a scanner at work.

 

[prcguy]

I've been running an NMO2/70B for many years, its so old the black paint is faded grey and it has a lot of missing paint. I had compared it to all the other dual band amateur antennas at the time from Diamond, Comet and the smaller Larsen closed coil version and it was the best performing of the bunch. It was center roof mounted on at least two prior vehicles and I might have had it on another earlier vehicle but my memory is failing.

I just got a new truck a few months back and put on my shiny new spare NMO2/70B that I've been saving for something special. Its cowl mounted and so far has tuned up and worked great.

 

[AK9R]

I recall reading somewhere that the whip with the open coil is prone to whistling on the highway.

I think these reports of "whistling" have more to do with the antenna's mounting location than the design of the antenna.

 

[kayn1n32008]

My 1/4 wave that whistles when it's foggy...

The NMO-2/70B whistles quite a bit when you drive a few hundred kilometers in ice fog. Then you get a "twang" as the build up gets to the point that it breaks off at highway speeds.

 

[kayn1n32008]

I think these reports of "whistling" have more to do with the antenna's mounting location than the design of the antenna.

It's the design, not the mounting location.

 

[mmckenna]

The NMO-2/70B whistles quite a bit when you drive a few hundred kilometers in ice fog. Then you get a "twang" as the build up gets to the point that it breaks off at highway speeds.

Yeah, I bet. I don't get that experience very often. What I have had is very large insects in Texas hit it and sound like they took the antenna off at the base.

 

[PrivatelyJeff]

It's the design, not the mounting location.

It’s both. I have it on my roof and I don’t whistle at all, no matter the time of year.

 

[AK9R]

If it was the design, it would whistle no matter the mounting location. But, that doesn't seem to be the case.

Seems like I did have an NMO2/70B mounted on the roof of Chevy S-10 pickup truck. When the weather was heavy with humidity, I remember hearing the antenna. In drier weather, it was quiet.

Whistle or not, it's a good antenna and I know several folks, including me, who are happy with them.

 

[prcguy]

I think they all whistle, it just depends on how sound proof your vehicle is and how far the antenna is from your ears.

If it was the design, it would whistle no matter the mounting location. But, that doesn't seem to be the case.

Seems like I did have an NMO2/70B mounted on the roof of Chevy S-10 pickup truck. When the weather was heavy with humidity, I remember hearing the antenna. In drier weather, it was quiet.

Whistle or not, it's a good antenna and I know several folks, including me, who are happy with them.

 

[mrweather]

I think they all whistle, it just depends on how sound proof your vehicle is and how far the antenna is from your ears.

My Charger's V8 generates a rumble so maybe it drowns out the antenna whistle.

 

[PrivatelyJeff]

I think they all whistle, it just depends on how sound proof your vehicle is and how far the antenna is from your ears.

maybe but my car is pretty crappy and when I had and antenna mounted to my rear window, it was loud but the one on the roof is quiet.

 

[W7GEL]

Considering getting a NMO2/70B but I like the clean lines of NMOQB and I like black VS stainless if I'm being honest Would anyone consider NMOQB I realize it's a bit more generalize in the bands 136-512 VS more targeted band on the NMO2/70B

 

[mmckenna]

Considering getting a NMO2/70B but I like the clean lines of NMOQB and I like black VS stainless if I'm being honest Would anyone consider NMOQB I realize it's a bit more generalize in the bands 136-512 VS more targeted band on the NMO2/70B

The NMOQWB is a quarter wave antenna, so you'd tune it for the frequency you'd want, in your case, center of the 2 meter band.
It will act as a 3/4 wave on the 70cm band, so it is an option if you have a dual band radio. I ran a VHF 1/4 wave on a Kenwood TM-D710 for many years.

Quarter wave antennas are quite broad banded, so it'll work well across the entire VHF spectrum and using the 3/4 wave UHF properties, quite well on UHF.

I ran one on my truck for a long time, and was quite happy with it. Only reason I don't have it on there right now is because I'm trying out some EM Wave antennas.

Here's a sweep of a 1/4 wave VHF antenna, looking at 136MHz all the way to 500MHz. You can see the dip at the VHF band, and another dip on the UHF band. Radiation pattern gets a bit less than ideal on UHF when using a VHF quarter wave, but it worked fine for me here surrounded by hills/mountains.

Here's a close up of just the UHF band:

Pretty good SWR on the 70cm and GMRS bands.


Here's the VHF sweep of the Larsen NMOQWB. This one was tuned around 156MHz since it's on my work truck, but you can see it stays well below 2:1 SWR across the VHF spectrum

 

[W7GEL]

The NMOQWB is a quarter wave antenna, so you'd tune it for the frequency you'd want, in your case, center of the 2 meter band.
It will act as a 3/4 wave on the 70cm band, so it is an option if you have a dual band radio. I ran a VHF 1/4 wave on a Kenwood TM-D710 for many years.

Quarter wave antennas are quite broad banded, so it'll work well across the entire VHF spectrum and using the 3/4 wave UHF properties, quite well on UHF.

I ran one on my truck for a long time, and was quite happy with it. Only reason I don't have it on there right now is because I'm trying out some EM Wave antennas.

I should mention this is my first mobile install so this is for sure a uphill learning experience right now, I originally was going to use a comet ant but it has an epic large coil right in the middle of the ant, I want this in a rig that goes off-road so coil loops mid ant height I fear will just be damaged by trees. Larsen seems to be well liked and bullet proof options. So I'm torn between the NMO2/70B much smaller coil trun at the top and the NMOQWB

The TH-D710GA is actually the radio I want to use in my rig, I should have mentioned that. APRS will more then likely be running as well.

When you said NMOQWB I assume your referring to NMOQB I'm not finding any listing in the Larsen for NMOQWB.

Appreciate the help