Antenna placement

[n7lrg]

I'll chime in on this one too. A dealer sold me one of these years ago and said something like, "The coax works as your ground plane". I tuned it via the adjuster in the tip, set it up and it did not perform well so replaced it with another REAL 5/8 ground plane. When I took the tram down I took it apart and the only thing inside the pvc was a thin piece of wire. I scrapped it out and kept the mount and put it in the "20 year box".

 

[rcraig114]

OK folks, figured I'd give an update. I purchased a Tram BR-29, a 6 Element Mobile CB Antenna Ground Radial Kit, and a metal bracket. I ended up having to purchase a 100' coax as the 50' wasn't quite long enough to go all the way and 75' wasn't easy to find. Regardless, I have attached pictures of the installation on my roof. I painted it black to avoid "Karen", lol. However, my radio is reporting high SWR on channel 1 and 40. Any ideas on what could be causing it? I did ground the mount by using a 10 gauge copper wire from the mount down into the attic and spliced into a ground on the light socket in the attic, but perhaps its not good enough?

Channel 1: SWR = 3.5
Channel 40: SWR = 5.3

Robert

 

[FPR1981]

OK folks, figured I'd give an update. I purchased a Tram BR-29, a 6 Element Mobile CB Antenna Ground Radial Kit, and a metal bracket. I ended up having to purchase a 100' coax as the 50' wasn't quite long enough to go all the way and 75' wasn't easy to find. Regardless, I have attached pictures of the installation on my roof. I painted it black to avoid "Karen", lol. However, my radio is reporting high SWR on channel 1 and 40. Any ideas on what could be causing it? I did ground the mount by using a 10 gauge copper wire from the mount down into the attic and spliced into a ground on the light socket in the attic, but perhaps its not good enough?

Channel 1: SWR = 3.5
Channel 40: SWR = 5.3

Robert

What's causing it is the fact that you're trying to use a mobile antenna outside the scope of its best performance and making complicated a process that shouldn't be. Get a base station antenna of some kind, any kind, other than that piece of crap Tram thing that looks like a 3-foot rubber duck antenna. OR get or build yourself a dipole and put it in the attic.

3.5 is horrendous and unsafe.
5.3 is absolutely unspeakable, embarrassing and shows that something is probably mechanically wrong along the way.

Abort mission.

 

[FPR1981]

And, I just saw that you painted it. Depending on the paint, it could have oxides (metals) in it, and it likely could have destroyed the antenna from the standpoint of functionality.

 

[rcraig114]

What's causing it is the fact that you're trying to use a mobile antenna outside the scope of its best performance and making complicated a process that shouldn't be. Get a base station antenna of some kind, any kind, other than that piece of crap Tram thing that looks like a 3-foot rubber duck antenna. OR get or build yourself a dipole and put it in the attic.

3.5 is horrendous and unsafe.
5.3 is absolutely unspeakable, embarrassing and shows that something is probably mechanically wrong along the way.

Abort mission.

I guess I'm a bit confused here. Why can't this antenna be used in this application?

Robert

 

[FPR1981]

I guess I'm a bit confused here. Why can't this antenna be used in this application?

Robert

It's not that it "can't." You just probably shouldn't. It's not made for that. And you're also creating significant loss issues with that length of coax.

It's that it simply is not made for that type of application, and you won't get the best performance out of it, nor for your needs. I promise you that a well-built dipole in the attic will eat this thing for lunch, even if you got the SWR down low.

 

[FPR1981]

You cannot "out tune" a 3.5 and 5.3 by conventional practices. You'd be cutting the antenna down to a stub.

My best guess is that absent a serious issue like broken coax, the paint probably ruined the antenna and is not allowing the power to be radiated. You have to be super cautious applying any type of finish to an antenna.

 

[rcraig114]

You cannot "out tune" a 3.5 and 5.3 by conventional practices. You'd be cutting the antenna down to a stub.

My best guess is that absent a serious issue like broken coax, the paint probably ruined the antenna and is not allowing the power to be radiated. You have to be super cautious applying any type of finish to an antenna.

OK. The paint might have ruined it so I'm willing to take a loss on that part. With the cables already run and the hole in the air vent, I'd like to keep an antenna mounted in this spot. What can I get that you'd recommend?

Robert

 

[mmckenna]

OK folks, figured I'd give an update. I purchased a Tram BR-29, a 6 Element Mobile CB Antenna Ground Radial Kit, and a metal bracket. I ended up having to purchase a 100' coax as the 50' wasn't quite long enough to go all the way and 75' wasn't easy to find. Regardless, I have attached pictures of the installation on my roof. I painted it black to avoid "Karen", lol. However, my radio is reporting high SWR on channel 1 and 40. Any ideas on what could be causing it? I did ground the mount by using a 10 gauge copper wire from the mount down into the attic and spliced into a ground on the light socket in the attic, but perhaps its not good enough?

Channel 1: SWR = 3.5
Channel 40: SWR = 5.3

Robert

That radial kit mounted at the antenna base is not acting as a ground plane. It's acting as some sort of capacitance hat.

Grounding the antenna mount isn't the same as having a ground plane. The reason your SWR is so high is due to lack of ground plane. On a -proper- mobile install, the vehicle body would act as the ground plane. What you have with the wire down to the electrical ground is some sort of funky dipole setup that isn't going to tune up well since the length is totally random.

Grounding the base to the light socket ground violates several National Electric Code rules off the top of my head.

The radial kit isn't nearly large enough to act as a ground plane on CB frequencies. It's way too small, even if it was installed correctly.

A proper base antenna would solve a lot of this, but I get that budgets and Karen's may not permit that. We all have to work inside certain limitations.

Here's what I'd do:
Ditch the radial kit.
Take 3 pieces of copper wire 108" or longer and connect them to the antenna base mount. Stretch them out straight as you can in opposite directions. 120º apart is ideal.

Get rid of the ground wire going to the light socket. You want that grounded to a ground rod.

 

[rcraig114]

That radial kit mounted at the antenna base is not acting as a ground plane. It's acting as some sort of capacitance hat.

Grounding the antenna mount isn't the same as having a ground plane. The reason your SWR is so high is due to lack of ground plane. On a -proper- mobile install, the vehicle body would act as the ground plane. What you have with the wire down to the electrical ground is some sort of funky dipole setup that isn't going to tune up well since the length is totally random.

Grounding the base to the light socket ground violates several National Electric Code rules off the top of my head.

The radial kit isn't nearly large enough to act as a ground plane on CB frequencies. It's way too small, even if it was installed correctly.

A proper base antenna would solve a lot of this, but I get that budgets and Karen's may not permit that. We all have to work inside certain limitations.

Here's what I'd do:
Ditch the radial kit.
Take 3 pieces of copper wire 108" or longer and connect them to the antenna base mount. Stretch them out straight as you can in opposite directions. 120º apart is ideal.

Get rid of the ground wire going to the light socket. You want that grounded to a ground rod.

A few questions and I can probably knock this out this weekend.

Take 3 pieces of copper wire 108" or longer and connect them to the antenna base mount. Stretch them out straight as you can in opposite directions. 120º apart is ideal. - Can I use any copper wire I have available (ie; some 14awg wire from a small DC project I did or something similar)?

Get rid of the ground wire going to the light socket. You want that grounded to a ground rod. - There is a ground outside where the cable company comes in. Can I attach the ground to that bus bar?

 

[mmckenna]

A few questions and I can probably knock this out this weekend.

Take 3 pieces of copper wire 108" or longer and connect them to the antenna base mount. Stretch them out straight as you can in opposite directions. 120º apart is ideal. - Can I use any copper wire I have available (ie; some 14awg wire from a small DC project I did or something similar)?

Yes, that'll work just fine. Make sure you attach them to the bracket that the antenna base is mounted to. They cannot be connected to the whip in any way.
You'll likely still have some SWR issues since the roof is sloped. Ideally you'd want the antenna mounted on the roof peak and the ground radials sloping downwards. Sounds like avoiding Karen is a higher priority.

Get rid of the ground wire going to the light socket. You want that grounded to a ground rod. - There is a ground outside where the cable company comes in. Can I attach the ground to that bus bar?

Maybe. You should be connecting directly to the ground rod, not another ground buss. You want any energy from a nearby lightning strike to have as straight and direct a path as possible to the ground rod.
To make it meet code, you would also need an entrance protector where the coax enters the home. That protector needs to be grounded to the same ground system as the rest of the house.

 

[FPR1981]

I'm still going with the paint being the issue. If it came from a spray can, it likely has oxides, which compromised the antenna. Besides the insufficient ground plane issue, the great lengths being gone to in order to make something work outside the scope of its use is NOT worth all the effort.

Dipole, man. Problem solved.

 

[rcraig114]

I'm still going with the paint being the issue. If it came from a spray can, it likely has oxides, which compromised the antenna. Besides the insufficient ground plane issue, the great lengths being gone to in order to make something work outside the scope of its use is NOT worth all the effort.

Dipole, man. Problem solved.

Not sure if it helps, but the spray paint contains Acetone, N-Butyl Acetate and Xylene. Greek to me.

Robert

 

[FPR1981]

Are you skeptical of the potential performance of a dipole? I was, for years, until I tried one. It almost seems too simple and too good to be true. But they work, damn well.

 

[rcraig114]

More like my ability to build one, not to mention my attic is meant for a toddler in gymnastics, lol.

Robert

 

[FPR1981]

You string them horizontally or in an inverse V shape. You can order them on ebay for 49 bucks shipped and thats with a working balun.

 

[rcraig114]

So this one would work? I can run the 50' cable thats now useless to this thing mounted between the rafters in the attic.

CB band Dipole Antenna for 11 meters Full-Wave High-impedance Base Station setup | eBay

Shop CB band Dipole Antennas for 11 meters, perfect for Full-Wave High-impedance Base Station setups. Ideal for enhancing your radio signal.

www.ebay.com

Robert

 

[FPR1981]

So this one would work? I can run the 50' cable thats now useless to this thing mounted between the rafters in the attic.

CB band Dipole Antenna for 11 meters Full-Wave High-impedance Base Station setup | eBay

Shop CB band Dipole Antennas for 11 meters, perfect for Full-Wave High-impedance Base Station setups. Ideal for enhancing your radio signal.

www.ebay.com

Robert

Absolutely.

 

[FPR1981]

CB 11 meter 1/2 Wave Dipole. ALL STAINLESS With 1:1 Current Balun, TRUE 2.15Dbi | eBay

A resonant half-wave dipole is typically fed with coaxial feedline and tuned to a specific area of a band. Its planned use is generally within that band. Basically, they ensure that the currents on each side of the dipole (balanced antenna) are perfectly even.

www.ebay.com

Get this one

 

[rcraig114]

Too late. I got the first one, lol.

Robert