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Pulse Larsen NMO-27 antenna plot

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mmckenna

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We hear a lot of people talk about the consumer grade CB antennas. We see a lot of people (me included) strongly recommend the Larsen NMO-27 antenna.

There are good reasons for both types, but here's some actual proof of what you get.

This is a 20 year old (at least) Larsen NMO-27 on a permanent mount NMO on the roof of a 2011 Ford F-150 crew cab. The NMO mount is near the back of the cab roof. Not the ideal position, but the center of the cab is reserved for my work radio antennas.

Plots were generated by an Agilent N9342C spectrum analyzer with a built in tracking generator.

First plot shows the 26.000MHz to 28.000MHz range.
Marker 1 is set to CB channel 1 26.965MHz
Marker 2 is set to CB channel 19 27.185MHz - center of the CB band.
Marker 3 is set to CB channel 40 27.405MHz
SWR readings are:
Channel 1 = 1.33:1
Channel 19 = 1.05:1
Channel 40 = 1.33:1
NMO-27_zpslybfreq8.jpg




Second plot show just the CB band. 26.965MHz to 27.405MHz range.
Markers are set as above. 1 on Channel 1. 2 on Channel 19. 3 on channel 40.
SWR numbers are a bit different due to narrowing the sweep gives me better control of their placement.
NMO-27_CB_zpssqoj2sg0.jpg




I don't have any 3/8x24 mounts or any of the consumer grade antennas to compare. But at least here's proof that these are excellent antennas when set up correctly.
 

krokus

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Very nice. A similar plot for antennas like the Wilson 1000, K40, and Firestik, would be interesting.

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JayMojave

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Hello mmckenna: Very good even WOW! Very impressive taking the SWR / S11 measurements, even more impressive is posting them. Thank you.

We all see and read many postings saying something about SWR, insertion loss, and even harmonics and such with opinion's and never backed up with real world measurements. And some do have the measurements but because of there cost and time investment, and what they show or indicate, they are not shared! And for good reason. Allowing one to set there like a coiled snake with the measured data in his notes only, allowing one to see who's says something different.

Yes making a S21 / Field Strength comparison test would be great of the different antennas.

Jay in the Great Mojave Desert
 

RRR

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A no-gainer "Unity" antenna.....
 

kayn1n32008

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A no-gainer "Unity" antenna.....

Actually, it likely exhibits negative gain because it is a loaded 1/4 wave. regardless, it is better than most CB antennas, does not weigh much and is low drag, unlike most CB antennas on the market.

Try mounting a firestic on your roof, and then go 110km/h down a highway...
 

n3obl

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I've used those on personal vehicles and few police cars that still have em. Works very well and the scope just proves it.
 

Project25_MASTR

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Actually, it likely exhibits negative gain because it is a loaded 1/4 wave. regardless, it is better than most CB antennas, does not weigh much and is low drag, unlike most CB antennas on the market.



Try mounting a firestic on your roof, and then go 110km/h down a highway...



Just because it's a loaded 1/4 wave antenna doesn't mean it exhibits negative gain. With antenna design there are three trade-offs; size, bandwidth and efficiency but you can only pick two. Optimize for size and efficiency, bandwidth goes to hell (great example are atomic clocks). Optimize for efficiency and bandwidth, size becomes larger.

Yes it's a smaller antenna but when it was designed, a great receiver was considered 12 dB SINAD at .3 μV (-117.5 dBm). I'd be willing to stake any of Larsen's gain claims against say…Firestik's 6 dB gain claim.


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mmckenna

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Well, either way, I'm not putting a 108" tall whip on top of my truck. I don't have any expectations of gain and I don't expect it to work as well as a 108" whip.

The NMO-27 is about as tall as I'm willing to go, even on the highway.

As for the Firesticks, Wilson, anything else, I'd love to do a side by side comparison, however I'm not going to install a 3/8x24 mount on my truck as I have zero use for that.
 
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