RV Roof "Ground Plane" Question

[Gashog]

I have an old '84 Sunflyer with sheet aluminum roof.
I haven't bothered to check for chassis ground because it's very very unlikely.
I have Googled and I have read what I can about antenna theory.
What's not sinking in is weather or not you need chassis ground for RF "ground".

Any thoughts?

 

[Robb]

In a vehicle, chassis ground becomes RF ground as far as the antenna/radio is concerned.

 

[Beetle]

Is this sheet aluminum one continuous piece, or several pieces? If the latter, they need to be bonded together well to make a continuous metallic surface. If the sides are metallic as well, bond them, too. Bond around any hinges like on doors - hinges are terrible at RF. Sliding contact means no contact.

 

[Gashog]

I'm not getting it.
I thought extra grounding of the roof to chassis was to short circuit possible RF ground loops.
That would be a resonance problem right?
Which wouldn't be a problem if the roof was isolated from chassis?
What's the difference between a counterpoised stationary antenna on a pole and 1/2 of a dipole on a 200 square foot sheet of aluminum 11' off the ground.
I can't get my head around it.
Would I have to run multiple grounding straps from the frame to the roof since it's 24' long?
I thought grounding straps only work if they are shorter then 8".
They would have to be at least 8'!
Running multiple wires to the frame destroys the resonance of the antenna by lengthening it right?
I've read about RV'ers gluing big sheets of various metals and foils to the rubber roofs of their RVs but I may be the only dummy on Earth who is trying to put a radio in a 35 year old aluminum roofed coach!
So it won't work without being grounded then?

 

[Gashog]

Is this sheet aluminum one continuous piece, or several pieces? If the latter, they need to be bonded together well to make a continuous metallic surface. If the sides are metallic as well, bond them, too. Bond around any hinges like on doors - hinges are terrible at RF. Sliding contact means no contact.

Yes it's one giant sheet of aluminum rolled out the length of the RV.
Edit: No the sides are plywood and fiberglass.
There is a cage of sorts but mostly the sides are non metal.

 

[Robb]

I'm not getting it.
I thought extra grounding of the roof to chassis was to short circuit possible RF ground loops.
That would be a resonance problem right?
Which wouldn't be a problem if the roof was isolated from chassis?
What's the difference between a counterpoised stationary antenna on a pole and 1/2 of a dipole on a 200 square foot sheet of aluminum 11' off the ground.
I can't get my head around it.
Would I have to run multiple grounding straps from the frame to the roof since it's 24' long?
I thought grounding straps only work if they are shorter then 8".
They would have to be at least 8'!
Running multiple wires to the frame destroys the resonance of the antenna by lengthening it right?
I've read about RV'ers gluing big sheets of various metals and foils to the rubber roofs of their RVs but I may be the only dummy on Earth who is trying to put a radio in a 35 year old aluminum roofed coach!
So it won't work without being grounded then?

It isn't shorting anything; running a bonding wire to the roof is only needed if it doesn't already have an electrical bond to the rest of the chassis. Doesn't really even need to be connected to the chassis.

If you are using a commercially made antenna; then all it really needs is to be centered on the roof (preferrably). The roof becomes the counterpoise to react with the vertical antenna. You get your antenna match set and then its off to the races.

What kind of antenna are you putting on this vehicle?
What kind of problem are you having?

 

[Gashog]

It isn't shorting anything; running a bonding wire to the roof is only needed if it doesn't already have an electrical bond to the rest of the chassis. Doesn't really even need to be connected to the chassis.

If you are using a commercially made antenna; then all it really needs is to be centered on the roof (preferrably). The roof becomes the counterpoise to react with the vertical antenna. You get your antenna match set and then its off to the races.

What kind of antenna are you putting on this vehicle?
What kind of problem are you having?

There's no problem since nothing is installed yet.
I have a 102" fiberglass whip and big spring mount.
The RV is my office on the farm.

The thing I don't understand is why the roof would need an electrical ground at all.
The radials on a base antenna don't have a redundant ground. (Redundant like other than the SO-239 connection).

I guess I just need to try it and if it doesn't tune with no electrical ground, I need to run one.
I'd like to understand the why and how though.

 

[Road Squawker]

I'm not getting it.
I thought extra grounding of the roof to chassis was to short circuit possible RF ground loops...Which wouldn't be a problem if the roof was isolated from chassis?...

Well, lets see, .......you have one conductor (the roof) separated from another conductor (the chassis) by an insulator, sooooo........

 

[Beetle]

There's no problem since nothing is installed yet.
I have a 102" fiberglass whip and big spring mount.
The RV is my office on the farm.

The thing I don't understand is why the roof would need an electrical ground at all.
The radials on a base antenna don't have a redundant ground. (Redundant like other than the SO-239 connection).

I guess I just need to try it and if it doesn't tune with no electrical ground, I need to run one.
I'd like to understand the why and how though.

There you go: experiment and see what works the best for you. Get a copy of the ARRL and/or RSGB Antenna Book

 

[Gashog]

Well, lets see, .......you have one conductor (the roof) separated from another conductor (the chassis) by an insulator, sooooo........

It's just one more plate of the capacitor right?
Did I win?

 

[Gashog]

What is "RF congruent"?

 

[Beetle]

What is "RF congruent"?

You seem to have found KØBG's website.
Think of it as all metallic structures being at the same RF potential at the same instant. This includes chassis, frame, doors, hood, and even down to the exhaust/tail pipe in many cases.

This doesn't mean that you absolutely HAVE to bond all of these things to a common point, only that others have found that their system performs "better" after having done the bonding, or as much of it as possible. This again means experimentation.

 

[Gashog]

I'm drilling the hole tomorrow.
I'll report back.

 

[Gashog]

Not quite as straight forward as I thought.
The roof is think.
I'll have to revisit this after I figure it out.
The regular stud is an inch too short.
Will report back