Antenna ground strap: how long is too long?

Tob · May 14, 2020

I am finally getting around to installing my CB stuff, and I'd like to mount the antenna on the swing away tire carrier, routing a ground strap to the rear crossmember. It will take ~30" of strap to route to the crossmember as shown.

The problem is I've read that the ground strap should be as short as possible. Is 30" too long?
Also, are any other potential problems mounting the antenna so close to the metal carrier? (part of the height of the antenna runs along side the height of the tire carrier when mounted here)

I do have a teraflex tail light mount, but I'll admit I'm not too eager to drill through the tub, in case I ever want to uninstall or mount the antenna elsewhere. I'd really rather mount the antenna to the carrier, but I'll use the tail light mount if I have to.

CharlesHS · May 14, 2020

What gauge copper wire are you using for the grounding wire ?
I would run a 10-12 gauge wire and clean the paint off the surface where you are attaching the grounding wire.
The close proximity of the antenna to metal will affect the SWR of the antenna when tuning to the center of the 11 meter band.
Make sure to have the antenna SWR checked and tuned before transmitting or you risk the chance of burning out the radio transmit finals due to too much returning wattage.

Tob · May 14, 2020

CharlesHS said:
What gauge copper wire are you using for the grounding wire ?
I would run a 10-12 gauge wire and clean the paint off the surface where you are attaching the grounding wire.

I haven't bought any ground wire yet, I'm still trying to decide which route to go: tire carrier or tail light

CharlesHS said:
The close proximity of the antenna to metal will affect the SWR of the antenna when tuning to the center of the 11 meter band.

I could mount it at the top of the tire carrier, but the dilemma is that would also require a longer ground strap, probably about 12".

CharlesHS said:
Make sure to have the antenna SWR checked and tuned before transmitting

How exactly do you do that? I thought you had to transmit through the SWR meter to see the reading to tune the antenna

Mr. Bills · May 14, 2020

The goal of the ground is to improve the ground plane of the antenna by creating a solid radio frequency ground from the antenna tab that the stud mount attaches to the frame of the vehicle versus trying to ground the stud mount or the antenna. Thus, if the antenna tab pictured above is welded to the tire carrier, making the antenna tab and tire carrier one piece of steel, you can run the ground wire from a location much closer to the hinge of the tire carrier. That should shorten the wire run substantially. Just make sure that you sand off enough paint at the antenna tab so there is a good RF path from stud mount to tab to where the RF ground wire departs the tire carrier for the crossmember,

Also, a radio frequency ground strap works much better than a ground wire because RF waves travel on the surface rather than through the wire and there is more surface area in ground strap than in a ground wire.

You can find tinned copper braid on Amazon. I buy it by the roll, cut it to length, and crimp ring terminals on each end.

This 1/2" braid works well. Also available in 1/4"

https://www.amazon.com/dp/B01BIBQ940/?tag=wranglerorg-20

pagrey · May 14, 2020

If you live near a junkyard allot of vehicles use pretty heavy ground straps on their hoods just like our Jeeps. That'll work and they probably wont charge more than a buck or two for it.

Tob · May 14, 2020

Mr. Bills said:
Thus, if the antenna tab pictured above is welded to the tire carrier, making the antenna tab and tire carrier one piece of steel, you can run the ground wire from a location much closer to the hinge of the tire carrier.

The tab is just a 90 degree bracket that can be bolted on in a few different spots. I think I’ll go with that one you linked and just cut it to length

CharlesHS · May 14, 2020

The higher up you can mount the tab for your antenna the better your receive and transmit signal will be, you will be less directional with your signal and less chance of reflection causing higher SWR.
You can purchase a cheap SWR meter at Radio Shack or even purchase a cheap one online unless you know a Ham Radio operator that has a Antenna Analyzer. You should adjust your antenna for the lowest SWR (1.1) around CH 19 or 20 which is the center of that band.
When I previously posted grounding wire; I should have said braided grounding strap. Just so accustomed when talking to Ham Radio friends they know that when a radio operator says grounding wire they mean braided strap.

Tob · May 14, 2020

Mr. Bills said:
This 1/2" braid works well. Also available in 1/4"

https://www.amazon.com/dp/B01BIBQ940/?tag=wranglerorg-20

Thanks for pointing me in the right direction. Does the grounding strap need some kind of protection or insulation around it? Also, where can I get the connectors to crimp onto the ends of the strap?

Jerry Bransford · May 14, 2020

You don't use regular wire for the antenna mount's RF ground strap. You need braided ground strap for that particular job. Go to an electronic or radio supply store to buy it by the foot. If you have a Fry's Electronics store try there though they don't seem to be stocking much lately.

Like this...

Tob · May 14, 2020

Jerry Bransford said:
You don't use regular wire for the antenna mount's RF ground strap. You need braided ground strap for that particular job. Go to an electronic or radio supply store to buy it by the foot. If you have a Fry's Electronics store try there though they don't seem to be stocking much lately.

Like this...

View attachment 161438

The closest thing we have to that would be Best Buy or Home Depot. I’ll most likely order something like the braided strap mr bills linked. The only thing I’m not sure about is what kind of connectors to buy for the ends of the strap

Mr. Bills · May 15, 2020

SecondChanceTJ said:
Thanks for pointing me in the right direction. Does the grounding strap need some kind of protection or insulation around it? Also, where can I get the connectors to crimp onto the ends of the strap?

No insulation/protection necessary.

Ring terminals can be found at Home Depot, Ace, and any auto parts store. I think I used non-insulated 12 ga. terminals for use with 3/8" studs with 1/2" tinned copper braid. Just roll the end of the braid, stick into ring terminal end ("screw in" rolled end rather than push in with blunt force), crimp.

Use can also use insulated ring terminals with or without the plastic insulation,

This would be a good time to get a "real" crimper - not one of these el cheapos:

Zorba · May 15, 2020

If the ring terminals are going to be exposed to the elements, crimp then solder. Trust me on this one.

Mr. Bills · May 15, 2020

You don't need to solder ring terminals for a RF ground strap made from tinned copper braid in a CB or ham mobile installation. A proper crimp and the resulting mechanical connection will be just fine. (Unless you are the kind of guy who regularly wears a belt and suspenders.) You will just make a mess and the solder connection will be more brittle than an ordinary crimped connection, particularly if your soldering iron doesn't have the wattage to bring up the temperature of the braid enough for the hot braid to melt the solder rather than melting it with the tip of the iron and the resulting cold joint.

Unless you are proficient at soldering you will be better off with just the mechanical connection of a crimp. Trust me on this one.

73.

Zorba · May 15, 2020

Mr. Bills said:
You don't need to solder ring terminals for a RF ground strap in a CB or ham mobile installation. A proper crimp is just fine. Trust me on this one.

I won't. Read my post above: IF ITS EXPOSED TO THE ELEMENTS.

Zorba · May 15, 2020

Mr. Bills said:
You don't need to solder ring terminals for a RF ground strap made from tinned copper braid in a CB or ham mobile installation. A proper crimp and the resulting mechanical connection will be just fine. (Unless you are the kind of guy who regularly wears a belt and suspenders.) You will just make a mess and the solder connection will be more brittle than an ordinary crimped connection, particularly if your soldering iron doesn't have the wattage to bring up the temperature of the braid enough for the hot braid to melt the solder rather than melting it with the tip of the iron and the resulting cold joint.

Unless you are proficient at soldering you will be better off with just the mechanical connection of a crimp. Trust me on this one.

73.

Well, yes - you do need to solder it correctly. Have you installed electronics and/or RF systems in an outdoor and/or marine environment? If you do not solder (correctly) the crimped connection, water WILL get into the joint, and WILL corrode it to the point of failure. I did this for a living for 25 years, in our environment, we'd solder, cover with meltable wall heat shrink, then a layer of self vulcanizing tape, and then sometimes even some RTV and the damn things would still often corrode and fail after a year or two. That was an extreme marine environment, I'm not suggesting anything that extreme here. Solder the damn thing if its going to be in a wet or moist environment or it WILL fail in time.

If you don't know how to solder, find somebody who does. It ain't rocket science. If you're worried about mechanical strength, reinforce it - but remember braid is particularly problematic in that it wicks water. I've had to actually draw sealant into an entire length of braid to prevent water from wicking where I didn't want it.

Mr. Bills · May 15, 2020

PS -

These are photos of a RF ground strap I put together for a non-Jeep ham mobile install in 2015. Crimp only. The strap and connection have been exposed to the elements for five years and work as well today as when the crimps were made. I used a bit of shrink tube around the ring terminals to protect the crimp connection, that's it.

For my LJ I didn't bother with the shrink tube. The ground straps have been underneath and exposed to the elements since mid-2017 with no issues.

These are RF ground straps. They carry RF waves on the surface of the braid, not electrical current through wire where voltage loss might be an issue. The purpose is to bond frame, body, hood, doors, engine block, etc. together electrically into one mass to improve the antenna ground plane. Multiple straps eliminate any risk that a single connection failure will have a measurable effect. Keep them simple. Don't overthink.

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Jerry Bransford · May 15, 2020

Just understand that soldering is no longer done as often as crimping is now, which is where many above are coming from. The problem is soldering, in most wired connections, causes problems (stress risers) that can cause the wire/cable to break. That's why few cable/wiring connections in our vehicles are soldered, and why even fewer are soldered in spacecraft and aircraft. Crimping is how it's most commonly done now. Properly done crimping has been shown through exhaustive analysis from organizations like NASA to be far more reliable which is why most wiring connections are now crimped and not soldered.

But for that particular ring connector for the antenna's ground plane connection, I'd probably crimp and solder it too due to the braided wire and the fact that a proper crimp style connector and proper crimping tool is not likely to be readily available or reasonable to buy for two ring connectors for that antenna's RF ground connection. There's 'ideal' and then there's 'reasonable' for single need. If the soldered braided RF ground cable breaks years down the road it would be an easy thing to re-do and all that would go wrong is the antenna's SWR would go up. It wouldn't cause a catastrophic failure.

I soldered my first connection in probably 1961 while building a kit AM radio and have done many thousands of them since during the years I spent in the electronics industry and as a hobbyist building various electronic gizmos. But while I still solder occasionally, I no longer solder all my connections like I used to.

Zorba · May 15, 2020

That's exactly right. You have to design for the worst case - aircraft and spacecraft don't have to worry about getting wet. If one is worried about vibration breakage - very valid in any vehicle - re-inforce as appropriate.
Its far easier to screw up a crimp than it is a solder joint, but of course I've seen plenty of both. Properly done, both are excellent. In the illustrated case, I'd be inclined to crimp, solder, then insulate the entire length of braid with heatshrink - preferably meltable inner wall heatshrink (at the ends at least), just to keep moisture out of the braid and prevent wicking. Probably overkill, but I don't like doing a job twice.