Larsen NMO27 reviews? Pictures?

[krokus]

https://www.theantennafarm.com/catalog/laird-technologies-abscancs-5587

so your suggesting adding the scanner antenna 150/450/800 to the side. Or find a more specific 700/800 antenna for that location on some sort of duplexer?

If you are only using two antennas, then the CB antenna in the center, and the tri-band on the other centerline spot. The off-center mount would have least affect on an 700/800/900 MHz antenna, compared to lower freqs.

 

[K6EEN]

See post #4 for what an NMO-27 looks like with a permanent NMO mount on a larger ground plane.

Here's the sweep across the band showing better than 2:1 (though not much better) with 1.73:1 SWR on Channel 19 or 27.195 MHz. Photo of Diamond K400 mount on trunk lip of small car also attached.

 

[doctorbubba010]

Here’s a picture of it on a 2016 FPIU center mount. With a Larsen NMO RG58 coax.
-CitySlicker

 

[n0iop]

Just got around to installing my NMODC27. I cut the whip for 10m.

The SWR is curiously high. Fender mount on my pickup, not ideal but I carry a canoe on the roof. The 6 meter MLB4700 works fine so I don't think I have a problem with the NMO or the feedline.

Advice welcome. I'm thinking of buying another loading coil but am not sure that will clear up the problem.

(Disregard the red trace as the input wasn't connected to anything but I hadn't shut it off). Here's the trace showing the SWR around 2.48:


Here's the 6m antenna on the same mount. Different scale on the trace, SWR under 1.7 for the band with the minimum SWR around 1.06:

 

[mrweather]

There may not be enough RF ground/counterpoise for 10m but enough for 6m at that mount poition. That might explain the different you're seeing.

 

[n0iop]

Thanks. I put in a bunch of bonding braids before figuring out that I hadn't calibrated the VNA properly. I had cut the antenna to the correct length, but the SWR is around 1.3 at resonance, which is close to what I would have expected.

 

[K6EEN]

I put in a bunch of bonding braids before figuring out that I hadn't calibrated the VNA properly.

When I added a DC grounding braid between the K-400 trunk lip mount base and a hard point on the car body inside the trunk, my SWR shot up from 1.73:1 to 3:1.

I had cut the antenna to the correct length, but the SWR is around 1.3 at resonance, which is close to what I would have expected.

Don't think you'll get much better than 1.3:1 on a pickup truck front fender bracket mount with this antenna. It was designed to be centered on the steel roof of a 1970s era police sedan with an NMO 3/4 inch hole mount. Once you deviate from the designed mounting configuration, the SWR starts to creep up.

 

[ur20v]

Wait 3 months when none of the infrastructure in the country is being maintained because of quarantine quagmire and CB will be a thing again.

Or 12 months when the sunspot cycle is back on the upswing?