Larsen Tri-band antenna base conversion

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mikebennett

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I've been looking for a good tri-band base antenna for 150/450/800 use.

After searching all the threads there doesn't seem to be anything noteworthy mentioned , at least that has decent 800 reception included.

I use a Larsen tri-band in the car and it works great so I'm thinking about trying to modify one of these for base use.

I'm thinking about mounting the antenna on a 16" pizza pan as a ground plane using LMR-400 cable. (The total cable run is about 75 feet)

I can either solder the cable directly to the NMO mount or use a conversion kit and go with an SO-259 connector. Do any of you antenna engineer types have any opinions on which would work best? I know it's better to use an N connector for applications above 512 mhz but this isn't an option so I'm not sure which method would be better in this case.

This sounds kind of bizzare but me and a friend used a pizza pan to mount a similar tri-band (40/150/450) about thirty years ago and it worked really well. The only difference was that we used a pole mounted amplifier on it also.

Mike
 

W9BU

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I have an NMO to base conversion adapter. It consists of an NMO mount with a collar around the base. That collar has four holes drilled into it and four set screws that are perpendicular to the holes. The adapter came with four whips that can be inserted into the holes, locked in place with the set screws, and then bent down at a 45 degree angle. This forms the ground plane for the antenna that's attached to the NMO mount. The other end of the NMO mount is a female UHF coax connector (ala SO-239). The adapter came with a bracket that attaches under the collar so you can mount the whole assembly to something. I thought this adapter was a Maxrad part, but I didn't find it on their web site.

I did find some NMO mounts for thick panels that have female UHF or female N connectors on them.
 

kb2vxa

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If you can't find a conversion kit you can always make one. How you do it depends on the antenna mount, I'm sure you can figure something out in the way of a small piece of sheet metal formed and drilled appropriately for mast mounting. Radials can be 19" lengths of 1/16" diameter brazing rod (copper wire bends in the wind) soldered to the corners of metal base plate. Hint, I got mine from a welder for free, I offered to pay but he wouldn't hear of it. I've adapted plenty of mobile antennas this way with good results, in fact I'm using an adapted 800MHz mobile antenna right now only with 3" radials. The difference is you'll need the longer ones for VHF, the higher frequencies will simply fall in line because there is no such thing as too long, only too short. BTW, you can bend down the radials or leave them straight, it really doesn't matter all that much.
 

mikebennett

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I have an NMO to base conversion adapter. It consists of an NMO mount with a collar around the base. That collar has four holes drilled into it and four set screws that are perpendicular to the holes. The adapter came with four whips that can be inserted into the holes, locked in place with the set screws, and then bent down at a 45 degree angle. This forms the ground plane for the antenna that's attached to the NMO mount. The other end of the NMO mount is a female UHF coax connector (ala SO-239). The adapter came with a bracket that attaches under the collar so you can mount the whole assembly to something. I thought this adapter was a Maxrad part, but I didn't find it on their web site.

I did find some NMO mounts for thick panels that have female UHF or female N connectors on them.
I have the base converter kit you've described. It's a BSAKIT however it's advertised for applications from
150 to 512 mhz. I'm not sure what I'd end up with on 800.

Where did you find the NMO mount with the N connector? That would at least solve my coax connection issue as I'd rather use an N connector.

I think I'll try that and see how it does, plus I may add the pizza pan or something smaller afterwards to see if it improves 800 reception.
 

kb2vxa

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"I have the base converter kit you've described. It's a BSAKIT however it's advertised for applications from 150 to 512 mhz. I'm not sure what I'd end up with on 800."

You missed something.

"The difference is you'll need the longer ones for VHF, the higher frequencies will simply fall in line because there is no such thing as too long, only too short."

In other words if it works on 150MHz it will work upwards including 800MHz.
 
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