Coax ground to backing plate or roof?

[groundwire]

How do you guys ground your coax in the mobile using a puck mount and backing plate? Do you ground the coax to the backing plate or between the backing plate and roof (direct roof connection)
Im grounded to the plate but looking at it, i was thinking the ground going thru the plate then capacitivly grounding to the roof cant be as good as a direct connection to the roof. So i took out my vom and like i thought, there is resistance between the two. I got a 1.2 ohm reading. What are your thoughts and why? oh yea, YES i took all the paint and primer off the whole square on the roof so it is raw metal to metal contact

 

[WECSOG]

That 1.2 ohms will indeed equal loss. Anything you can do to improve the connection to the roof will help.

 

[groundwire]

Yup, and im thinking thats where my swr issue is comming from

 

[2NC995]

The 1.2 ohms doesn’t mean much. Could be your leads, or just the connection. Can you get a 0.0 touching the leads together?

It would be an open at DC if connected only via capacitance.

 

[groundwire]

My test leads have a .3 ohm resistance so my 1.2 ohm reading is minus the the lead resistance

 

[2NC995]

What is the backing plate made out of?

 

[groundwire]

Im 95% shure its aluminum. Its from breedlove mounts

 

[Tallman]

I would go to the backing plate.

 

[M0GVZ]

With the puck mounts you use one of the mounting bolts.

The reading you get with a multimeter doesn't mean anything as it's only measuring a DC resistance and AC/RF works completely differently. Also too late now but you shouldn't have removed the paint and primer as you've removed the zinc rustproofing.

 

[M0GVZ]

That 1.2 ohms will indeed equal loss.

At 0Hz DC but he's not transmitting at 0Hz.

 

[groundwire]

The coax shield is connected to one of the bolts.

 

[543_Dallas]

Connect the shield to the backing plate with the puck bolts. I split the braid and connect to 2 bolts with soldered on ring terminals. Keep the center conductor that sticks out as short as possible.

Sand the bottom of the cab to bare metal where the backing plate makes contact. Use your favorite compound between the roof and backing plate to prevent corrosion. I've had no issues with the Noalox on the puck I did almost 10 years ago.

 

[groundwire]

Haha, thats a coincidence, thats exactly how i have mine done. Except the braid is omly on one bolt.

 

[WECSOG]

At 0Hz DC but he's not transmitting at 0Hz.

If there's resistance at DC, that resistance is still there with AC. Granted, capacitance between the plate and the roof will act in parallel (bypass), but that is not even close to a perfect capacitor. It's a good idea to get that resistance as low as possible.

 

[Handy Andy]

Wow...Went to the site to find what you're looking at...

Aluminum - hmm...lots of them are Anodized, so the issue of good ground and the type of mount used, both go hand in hand.

Are you using this mount?

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When I see "Backing Plate" since the above is a 3-hole punch...

I take it you also are installing this...

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Is that correct?

Because I found this - which was helpful but not sure what you're up against...

But this doesn't look exactly like the one I'm thinking you have...​