What do you think of this NMO mounting location?

[BonziBuddy]

I have an Antenex Laird C27 CB radio antenna that I want to NMO mount to the fender of my truck. I chose this over a lip mount because it's more low profile on the truck and not in my field of vision.

This is what the spot looks like. I will be using a greenlee hole punch to carefully make the hole. The metal is solid and does not flex. There is nothing underneath it that will effect the placement of the mount either. Also it is naturally level with the ground and makes the antenna stand perfectly straight.

What do you think of this spot? do you think it is too close to the cab and will result in a high SWR?

 

[wyomingmedic]

I doubt the SWR will be too screwy. But to be safe, I would just get the antenna on a magmount and set it in that location and give a quick check. There may be some surprises.

As for the location itself, is that a Toyota? If it is, the metal there is SUPER weak and flimsy (a common problem with the newer Toyotas). That would be my biggest concern. But if you think it will work after doing some SWR tests and some strength tests, I think the location would look great.

WM

 

[rfradioconsult]

Shound work out fine, just verify the VSWR because of the proximity to the door post. Note that at low frequencies a mag mount and a installed antenna wil tune differently due to the lower coupling coefficent at the lower frequencies for the mag mount. Make sure you use only a 3/4 inch Greenlee punch and install the mount from the top, don't try to push the mount up from the bottom.

 

[davidgcet]

probably work ok, but not the best in teh world since you don't have much ground plane. 27 mhz NEEDS a larger ground plane, so optimal mounting is center of the roof. expect some directionality from your mounting point, but it should only affect long distance back thru the cab.

 

[RadioWARE]

It's a marginal antenna at best for 10-11m so don't go too crazy. Anything under 2:1 SWR will be fine.

 

[KC4YIN]

if you are considering punching a hole in the truck in that location, why not go ahead and do it in the center of roof where it will yield superior performance as compared to where you plan on putting it.

 

[N8IAA]

Maybe he has other antennas to mount on the roof? I used a trunklip mount on my F-150's hood for years. Never a problem with the swr. Used another on the third door with a shorty Larsen dual band antenna. I wouldn't worry about the mount there at all.
Larry

 

[kb0nly]

I wouldn't worry about that location but i would make one change to others suggestions for installing the mount...

Get a 3/8" hole NMO mount, the bigger the hole in that location the weaker your making it. The 3/8" inch mounts are easy to install with a Unibit (stepbit for others) and just go slow, use a center punch to mark the hole, drill slow, remove shavings as you go or tape off the area with some masking tape to stop the filings from the drill bit marking up the paint.

If you got a 3/8" inch hole mount for thick locations you can add a fender washer or two on the bottom side to even further stiffen it up.

A 3/4" hole takes too much metal out in locations like that.

 

[ampulman]

I'd be concerned with the proximity of the alternator to the antenna. Might want to try a mag mount with the engine running.

Amp

 

[jim202]

I would be concerned that you have enough of a ground plane under the antenna to allow it to function normally. Being a low band antenna, it will be looking for a good amount of metal under and around it to work as it was designed.

My bet is the SWR will be on the high side and there will not be much you can do to lower it. If by some chance of luck you do get a low SWR, I would not expect the antenna to function very well.

Jim

 

[mrweather]

Aesthetically it looks good but I'm not sure you'll be happy with performance. Low-band antennas need a lot of metal to work properly. Plus the close proximity of the A-pillar I think will adversely interact with the antenna.

 

[RodStrong]

If you are gonna drill, I would not drill there, and would definitely do it on the roof. Good luck either way.

 

[key2_altfire]

Looks good to me. On VSWR. When I installed my mobile rig I had an RF engineer where I work help me tune the antenna using an Agilent network analyzer. Moving the antenna near to the A pillar did not really change it much. The Agilent would show some change but it was only like 0.1 dB return and most of that was outside ham bands - seems my Subaru A pillar post is a selective 700 mHz reflector. ;-)

BTW even though VSWR wasn't really changed, this is not to say it could be changing your radiation pattern or attenuating incoming or outgoing signal.

 

[N4UYV_Al]

I can't see a problem with mounting in that location myself.. I'd just make sure the door was closed while tuning the antenna....

 

[zz0468]

The radiation pattern is going to be pretty screwy if you mount it there.

 

[mm]

I have the CW27, wide band version of that antenna and the similar 6 meter version on a Toyota 4 -runner and I found that engine noise was hard to knock down at any location near the front of the vehicle on both bands.

Even though the CW27 version is 67 inches long at 10 meters and of course shorter at 6 meters, I still have mine mounted near the top of the rear hatchback which works very well on both bands.

I would run some receiver sensitivity test with a sig generator coupled in at the antenna end, this will give you a good idea on how noisy a front of the vehicle mounting location can be.


Mike