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Larsen Multi-Band antennas

mmckenna

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I ordered two Larsen multi-band antennas recently to try out for a project at work.
NMO-150/450/758SF
NMO-150/450/800SF

I brought them home from work along with my Agilent spectrum analyzer with tracking generator so I could sweep them on my truck.
Antenna mount is a Larsen NMO-HF installed dead center on the roof of a 2018 F350 Crew Cab, so near perfect ground plane on all frequencies VHF and above.

For reference, here's the package label and under side of the antenna showing the part numbers:




 

mmckenna

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Out of the package, I notice that these antennas look identical. One of the is about 1/8" longer than the other, but center coils are in the same place. Confirmed that they are labeled as two different models, so not sure...

 

mmckenna

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So, here's the traces for the NMO-150/450/758SF version

Full spectrum:


VHF band:


UHF band:


700-960 spectrum (yes, I know this specific antenna is only rated at 750-870, but using the same frequencies so we can compare them side by side….)
 

mmckenna

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OK, here's the NMO-150/450/800SF version:

Full spectrum:


VHF band:


UHF band:


756-960MHz (…again, YES, I know, this antenna is rated at 806-960, but doing this so we can compare the two…)
 

mmckenna

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So, here's where it gets interesting….

I don't know if Larsen made an error and labeled/shipped the exact same antenna with different tags, or if they sell the exact same antenna under different part numbers for marketing purposes.
No idea if this is an error on their part or not. I'll try to remember to call them and see what they say. Maybe it's just a simple error.

Here's the 758 version overlaid on the 800MHz version. Really hard to see the difference. Blue trace is the 758, Yellow trace is the 800...


As for the photo of the two antennas in my earlier post, the longer one (about 1/8" difference) is the version that says it's rated for up to 960MHz, so not sure if it's a variation in manufacturer, or just the way it is. Like I said, a call to Larsen is in order.
 

mmckenna

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So, all that aside, nice looking antennas. The base design is a bit nicer than the older NMO models. The design gives you a bit of extra grip for removing them.

The 'pogo-pin' center contact looks good, better than some older designs by other manufacturers. Will have to see how well they last.

The spring has a nice black wrinkle coating on it. Have to see how long that lasts or if it chips off.

Spring is similar to the older Larsen antennas in terms of stiffness.

Whip is flexible and looks like it'll take some pretty healthy hits.

Center coil is flexible, rather than some antennas that have a hard plastic covering, this one flexes.

I'll be trying these out at work on some multiband radios to get an idea how they compare to other options.

Testing shows that these would be just fine for amateur radio use and provide a < 2:1 SWR on the 2 meter, 70cm and 900MHz. Acceptable SWR for GMRS, also.
However, these are obviously designed for LMR use, and where the major dips exist on the SWR are centered on the public safety bands.

Since I'm only running a VHF radio in my personal truck, I removed these antennas after testing and put my 1/4 wave VHF back on.
Would love to hear others experience about using these as scanner antennas.
 

mmckenna

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Just for giggles, I swept one of them all the way down to 30MHz:


Yeah, what we all expected. Just to head it off, no, it's not going to work for CB, 6 meters, 10 meters. It's going to suck trying to listen to low band/California Highway Patrol unless it's a really strong signal.
 

nd5y

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I want to see radiation patterns across all the bands they are designed for (or happen to have low SWR on).
I wonder if Larsen even measured them on an antenna range.
 

TexTAC

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I have the older NMO150/450/800 (no pogo and no SF). It is a great scanning antenna for where I live as it covers the Dallas PD and FD frequencies as well as the major P25 systems in my area. I noticed the same thing regarding SWF curves with the NMO150/450/758 (I.e they look the same)! For ham radio transmissions on 2m and 70cm however, they are tuned for the wrong frequency range. I use a Larsen NMO2/70B for my transceiver and that works great for amateur bands.
 

mmckenna

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I use a Larsen NMO2/70B for my transceiver and that works great for amateur bands.
Yeah, right antenna for the job. However, those are bigger antennas than these and actually have some gain. I'd expect it to work better.

Glad to hear your scanner liked the older version. I've got an old 895xlt sitting in my office and might slap one of these on there.
 

mmckenna

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Looking at the manufacturers spec for both those antennas, they are supposed to be the same length. Not sure where the tuning difference is between the 758 and the 800 model.
Since one of them is a bit longer, I'm starting to wonder if their quality control is starting to slip a little bit. The ball at the end has a hole through it where the whip goes. On their older antennas, they'd cleaned them up so you couldn't see any of the whip at the top. These, not so much.

I've liked Larsen antennas for a long time. I hope they don't go cheap on us.
 

mmckenna

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Something like that. They appear to have several offices in US and Europe, and some manufacturing in Taiwan.
I don't have a problem where the manufacturing is done, as long as they keep the QC up.
 

TexTAC

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I haven’t seen their newest antennas, but the ones I have are very well made. Could the 1/8” difference in lengths just be the difference in how much of the whip is set into the base with the set screw?
 

mmckenna

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I generally agree with that, but unfortunately, the closer you get to China, the worse the QC.
It can entirely depend on how much QC the company is willing to pay for. I have several Milwaukee power tools that were made in China, and several of them are 12+ years old and used heavily. None of them have failed.
 

mmckenna

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I haven’t seen their newest antennas, but the ones I have are very well made. Could the 1/8” difference in lengths just be the difference in how much of the whip is set into the base with the set screw?
Absolutely, but if you look at the comparison plot, there's very little difference. Spec sheets show they are both the same length. I could have played with the tuning, but that would have impacted all the bands.
 

TexTAC

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Check out the first post in this older thread. Using Pulse Larson data sheets, the 800sf and the 758sf have slightly different heights. Also Pulse Larson’s own SWR curves are very similar over a period of several years for the various models. I was thinking they just marketed them wrong initially and realized the SWR curves allowed them to market them with a broader tuned frequency range (I.e SWR<2). but that doesn’t explain why they still market and sell both models.

 
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