Mounting NMO antenna to aluminum truck cab?

[JohnDeere7920]

Hey everyone. Had a quick question about using one of the dreaded magnetic hockey puck NMO mounts in my 17 F350 which is of course aluminum. Obviously magnet won’t stick to the top of the cab so I’ve put some felt down with double sided tape to stick it there for my ground plane. 
 

question is the felt and double sided tape interfering with good grounding of the antenna? I really don’t want to screw anything through the top of my cab to secure the antenna mount to. Right now radios work in excess of 5 miles but if somehow fixing this would get me some more miles that would be great. I don’t have an SWR meter to check any of the specifics. Just bought MXT500 radios for farm use so communicate is kinda important at times. 
 

what’s everyone done to remedy the aluminum cab issue? Thanks I’m new here btw so bear with me as I learn these things. We’ve had business band radios for years but they have stopped working and now going another direction since we can’t fix and program our own radios. 
 

WSJV395

[RoadApple]

4 hours ago, OffRoaderX said:

WARNING!!! "some people" are going to try and convince you that your setup will not work, nobody will hear you and it will burn-up your radio, because you do not have 6 inches of metal/ground plane in all directions under the bottom of the antenna..

As you probably already know by your real-world experience of actually using your setup, they can be ignored..  "some people" have difficulty differentiating from "the best" or "perfect" that they read about in a book and "plenty good enough for normal people outside in the real-world".

 

Yeah, you are exactly right!  I heard that proclamation/warning and chose to ignore it.  I'm not a radio purist so as long as it works reasonably well, I don't really concern myself with all the technical perfection (usually only detectable with test equipment).  The photo I posted above shows the 3rd brake light mount with a dual band 2m/70cm antenna, but most of the time I use a little 6" Tram 1126-B 1/4wave antenna.  I like that little Tram because it is very low profile, and most folks do not even notice that I have an antenna up there.  My SWR is 1.2:1 on my Btech 20W mobile and it works great for my real-world purposes on both GMRS and 70cm. 

In fact, based on my experience, I might argue that for UHF, ground plane is often over-rated.  I can drive in circles, presumably transitioning between lots of ground plane (to the front) and arguably zero ground plane (to the rear) and the folks I'm talking to usually can't tell the difference.   That's good enough for me!
 

[nokones]

9 hours ago, WRYZ926 said:

Man I could have some fun when passing people with third brake light mounts if that was actually true. 

I remember doing some radio testing on 800 Mhz in the very early 80s. I was driving up S.R. 99 in Fresno and this Cadillac with Texas plates kept hitting the brakes in front of me. Then I realized that he was doing this everytime I keyed the 800 Meg radio.

I drove up along side thinking he may be a tad impaired and I noticed that he had a box on top of the dashboard and a light would light up when I keyed the radio.

The box was a Fuzzbuster (radar detector) and obviously he thought he was being targeted for speeding. So, I told my partner in crime let's have some fun.

With the freeway speeds being 55 MPH in those days, we let him get up to about 80 and we keyed the mic and he slowed down to 55 MPH and we kept it keyed for several miles. I bet he was getting impatient going 55 MPH.

We pulled off the freeway because we needed to get some gas and that was enough fun for the day.

It's a true story, I know because I was there causing all this fun. No, the caddy did not have any bull horns on the front of his car.

[WRYZ926]

@nokones that is hilarious. I would have done the same thing and messed with the guy.

That is better than my friend driving through neighborhoods and scrambling everyone's TV's with his CB and linear amp when we were in high school.

Since statute of limitations has passed. While at Ft Devens, we would have to test the airborne electronic warfare equipment and we would occasionally have some fun messing with the locals.

[nokones]

It really amazes me that "Some People" get the same VSWRs on a cheap POS Pandaland antenna with a spread difference of almost 20 megs. Really? Wow, that is amazing that any antenna can do that.

[nokones]

1 minute ago, WRYZ926 said:That is better than my friend driving through neighborhoods and scrambling everyone's TV's with his CB and linear amp when we were in high school.

 

 

Done that too. Although, we didn't have enough power to turn on the street lights when we keyed, it definitely caused the picture on TV Channel 2 to wiggle a lot.

[GreggInFL]

Modern epoxies have a tensile strength of 3000+ psi. Just glue it down, if you don't mind it staying there forever.

[Lscott]

50 minutes ago, GreggInFL said:

Modern epoxies have a tensile strength of 3000+ psi. Just glue it down, if you don't mind it staying there forever.

Depends on how much you use. The magnet mount depends on the capacitive coupling from the base to the sheet metal for the ground plane connection. Adding in a layer of glue increases the thickness and thus reducing the coupling. This could mess up the match.

[SteveShannon]

1 minute ago, Lscott said:

Depends on how much you use. The magnet mount depends on the capacitive coupling from the base to the sheet metal for the ground plane connection. Adding in a layer of glue increases the thickness and thus reducing the coupling. This could mess up the match.

Perhaps an iron or aluminum bearing epoxy would negate that issue.  I don’t know of any commercial epoxies that contain aluminum powder, but JBWeld has iron powder in it.  

[RoadApple]

2 hours ago, nokones said:

It really amazes me that "Some People" get the same VSWRs on a cheap POS Pandaland antenna with a spread difference of almost 20 megs. Really? Wow, that is amazing that any antenna can do that.

IDK, I have a few "POS Pandaland" antennas, and they seem ok...   (at least for my purposes).   

At 460Mhz a 1/4 wave whip on an NMO mount is electrically very simple (no loading coils, etc.).  It's not that the SWR doesn't change from the resonate apex of the tuned bell curve, it is a matter of how much it changes and if that change falls outside of a safe operating range or results in a humanly noticeable performance degradation.   

I'm no metallurgist, and perhaps there is much I don't understand on this topic, but at the relatively low <=50-watt power level used in GMRS, it would seem that a minor materials differences between a Pandaland vs other name brand whip antenna would have a negligible impact and be functionally imperceptible in most real-world scenarios.  Anyway, that has been my experience.

All I'm saying is that sometimes it is ok to give a Panda a chance!! 

[WSEL330]

3 hours ago, SteveShannon said:

Perhaps an iron or aluminum bearing epoxy would negate that issue.  I don’t know of any commercial epoxies that contain aluminum powder, but JBWeld has iron powder in it.  

If we are going that far....braze a plate down.

[SteveShannon]

5 minutes ago, WSEL330 said:

If we are going that far....braze a plate down.

Honestly if you’re going to do anything that’s more permanent than peel and stick you should really just punch a hole and install a through-hole NMO mount like @gortex2 showed. 

[Lscott]

4 hours ago, SteveShannon said:

Perhaps an iron or aluminum bearing epoxy would negate that issue.  I don’t know of any commercial epoxies that contain aluminum powder, but JBWeld has iron powder in it.  

Easy way to test is stick a thick sheet of plastic under the antenna magnetic base while the vehicle is stationary. If the match still looks OK then the glue won't make much of a difference.  

[WSEL330]

21 minutes ago, SteveShannon said:

Honestly if you’re going to do anything that’s more permanent than peel and stick you should really just punch a hole and install a through-hole NMO mount like @gortex2 showed. 

Yeah, yeah and use lag bolts with construction glue! lol