Ground radial for mirror-mount CB antenna on semi truck?

[corneileous]

Being that I’ve been having all these conversations here lately about antennas, ground planes and coaxes for my home scanner, I got this crazy idea to go on Google to see if they make groundplane kits for CBs and well and I came across this little ground radial from Walcott radio and wondered if it might work to help maybe improve my SWR.

It’s funny, in all of my close to 15 years driving big trucks, I don’t think I’ve ever seen anything like this at the base of an antenna that’s typically almost always on the side view mirrors of these trucks.

As far as my set up, I’m not using a fancy radio at all. It’s just one of them cheap little $20 cobras you can buy at Walmart basically the same as your typical cobra 29 but it has no noise filter or noise blanker button, no mic gain knob, just a simple digital channel display, on off/volume knob, RF gain/squelch knob and that’s pretty much it.

As far as my antenna/coax, I’m just using a plain 18 foot piece of coax with a 3 foot fiberglass fire stick antenna that has an adjustable top that I have done the SWR calibration on and if I remember correctly, my SWR is set to probably 1.6 on channel 40 and like 1.5 on channel one so would installing this little device help?

 

[mmckenna]

Did you read the description?

Even the seller is skeptical. Since there is no connection to ground, it's not a ground plane. It probably plays with capacitive coupling of the antenna to the ground under it to affect tuning.

You are not going to get a suitable ground plane under a CB antenna on any road legal vehicle. There just isn't enough room. You'd be better off bonding the mirror mount to body ground.

 

[corneileous]

Did you read the description?

Even the seller is skeptical.

I read the description but from my impression, I just took it like this was just something they’ve never heard of which in my uneducated opinion doesn’t necessarily say it wouldn’t work just because even that CB shop had never heard of it and not only that, there’s not really a whole lot of truck drivers anymore who take their CB radios serious.

Most people now days as long as they can talk to a truck directly in front of them, behind them or across the median, if they even have their CB turned on is really all they care about so in other words, I really wouldn’t expect anyone to know about something like this, even from the truckers who actually take pride and their CB set ups. Maybe they’ve never heard of it either. Doesn’t automatically suggest that it wouldn’t work just because they’ve never heard about it.

Since there is no connection to ground, it's not a ground plane. It probably plays with capacitive coupling of the antenna to the ground under it to affect tuning.

Well, I guess I don’t really know how this thing works and where exactly it mounts to, but my antenna mount is grounded to the frame through the mirror bracket and that the only part that’s not grounded to the chassis is the antenna itself and the part on top of the antenna mount that the antenna screws into.

You are not going to get a suitable ground plane under a CB antenna on any road legal vehicle. There just isn't enough room. You'd be better off bonding the mirror mount to body ground.

So does this just apply to CB radios or is this pretty much any kind of two-way radio on a vehicle? Cop cars having an antenna mounted to their trunk lid or up on the roof of their cars, doesn’t provide enough of a suitable ground plane?

 

[prcguy]

In the mid 1970s I was a radio/car stereo installer and experimented with an upside down grounded CB whip as a counter poise for a mirror mount CB antenna and it works well depending on the makeup of the cab. I've installed quite a few of these on big rigs using things like a 2ft Firestick as the grounded counterpoise.

This idea seems to work better on fiberglass cabs but metal cabs tune up ok if the mirror holds the antennas far out from the cab. Running the upside down whip just a few inches away from a metal door can make the antenna system harder to tune up and I didn't have the luxury of an antenna analyzer or ferrite chokes back then.

 

[AB5ID]

Love the description "Transmit in style with a ground radial kit for your CB antenna. Installs under the antenna, and above your stud to provide "ground" radials for your antenna. Not sure how additional radials can be called "ground" when they're touching your antenna? We're not sure either,..."

 

[prcguy]

Love the description "Transmit in style with a ground radial kit for your CB antenna. Installs under the antenna, and above your stud to provide "ground" radials for your antenna. Not sure how additional radials can be called "ground" when they're touching your antenna? We're not sure either,..."

They are obviously not ground radials and they will effectively lengthen the antenna since they are connected to the radiating part of the antenna. Since there are several radials going different directions they will not try and radiate in a horizontal plane, instead they will just slightly lower the resonant frequency antenna and add more capacitance to ground.

 

[corneileous]

Love the description "Transmit in style with a ground radial kit for your CB antenna. Installs under the antenna, and above your stud to provide "ground" radials for your antenna. Not sure how additional radials can be called "ground" when they're touching your antenna? We're not sure either,..."

They are obviously not ground radials and they will effectively lengthen the antenna since they are connected to the radiating part of the antenna. Since there are several radials going different directions they will not try and radiate in a horizontal plane, instead they will just slightly lower the resonant frequency antenna and add more capacitance to ground.

Both of what y’all say actually does make sense. I guess I didn’t read that part of the description on where they describe where this piece goes but now that I think about it, just like with the antenna and ground plane kit that I intend to buy for my police scanner at home, the ground plane kit is what actually has the coax connected to and that there must be some kind of insulated part Between the top of the ground plane kit and where the antenna actually attaches to so like I said, I kind of understand where you guys are coming from.

So I guess in order for this thing to make sense, the bottom part of my antenna mount that has the PL 259 connector on it would have to be in contact with that so-called ground plane and then on top of that, the part of my antenna mount that actually threads onto the base of the antenna would have to be isolated from this part we’re talking about, correct?

 

[prcguy]

Both of what y’all say actually does make sense. I guess I didn’t read that part of the description on where they describe where this piece goes but now that I think about it, just like with the antenna and ground plane kit that I intend to buy for my police scanner at home, the ground plane kit is what actually has the coax connected to and that there must be some kind of insulated part Between the top of the ground plane kit and where the antenna actually attaches to so like I said, I kind of understand where you guys are coming from.

So I guess in order for this thing to make sense, the bottom part of my antenna mount that has the PL 259 connector on it would have to be in contact with that so-called ground plane and then on top of that, the part of my antenna mount that actually threads onto the base of the antenna would have to be isolated from this part we’re talking about, correct?

The link you supplied from Walcott is a scam and the entire radial system is connected to the hot part of the antenna. Its not a ground plane in any way. A typical ground plane kit for a VHF/UHF scanner antenna, usually NMO, will have ground radials that are connected to the ground side of the mount and that would be an actual ground plane.

 

[corneileous]

The link you supplied from Walcott is a scam and the entire radial system is connected to the hot part of the antenna. Its not a ground plane in any way. A typical ground plane kit for a VHF/UHF scanner antenna, usually NMO, will have ground radials that are connected to the ground side of the mount and that would be an actual ground plane.

OK, so then that’s basically what I said right, that being that this thing installs in such a way where it makes contact with the antenna that, instead of creating a ground plane like it’s supposed to, it would essentially make the antenna a lot longer than it needs to be, correct?

I guess perhaps there is a reason why I’ve never seen anything like this and why Walcott radio would even bother selling it.

 

[prcguy]

OK, so then that’s basically what I said right, that being that this thing installs in such a way where it makes contact with the antenna that, instead of creating a ground plane like it’s supposed to, it would essentially make the antenna a lot longer than it needs to be, correct?

I guess perhaps there is a reason why I’ve never seen anything like this and why Walcott radio would even bother selling it.

It will make the antenna a little longer being at the base. If you could put it at the top it would have a much bigger effect on lengthening the antenna.

 

[mmckenna]

I read the description but from my impression, I just took it like this was just something they’ve never heard of which in my uneducated opinion doesn’t necessarily say it wouldn’t work just because even that CB shop had never heard of it and not only that, there’s not really a whole lot of truck drivers anymore who take their CB radios serious.

Maybe.

However, I've discovered that there are those that want an antenna to look weird so it stands out or it suggests some sort of voodoo technology that magically makes a cheap add on make a radio work better. This sort of stuff is very common in the hobby side of radio, especially amateur radio. The more ugly/odd an antenna looks, the better it must work.
I seriously think I could make a lot of money by producing really ugly antennas and then writing a good B.S. explanation of why it works better than the competitor, without actually backing it up.

Not a dig at you, just pointing out that a lot of people view antennas as some sort of black magic that no one really understands, so odd/strange products get a lot of attention. In reality, the physics are pretty well understood, yet hobbyists don't want to put the effort/time into a good antenna installation, and would rather buy magic snake oil products that make them think they are getting something.

A properly tuned antenna on a good ground plane all properly installed will work better than snake oil add ons.

Most people now days as long as they can talk to a truck directly in front of them, behind them or across the median, if they even have their CB turned on is really all they care about so in other words, I really wouldn’t expect anyone to know about something like this, even from the truckers who actually take pride and their CB set ups. Maybe they’ve never heard of it either. Doesn’t automatically suggest that it wouldn’t work just because they’ve never heard about it.

It's more about image, as I was suggesting above. With the physics involved, it's really hard to make an antenna stand out from the competition, so hobby oriented antenna manufacturers will turn to things like this to sell antennas/products.

I wouldn't spend money on that, but if it makes someone feel good about their radio setup, then good for them.

Well, I guess I don’t really know how this thing works and where exactly it mounts to, but my antenna mount is grounded to the frame through the mirror bracket and that the only part that’s not grounded to the chassis is the antenna itself and the part on top of the antenna mount that the antenna screws into.

DC grounding and RF ground planes can be different things. Grounding your mirror bracket is good, but getting a well working setup when the antenna is mounted out at the end of a long arm sticking off the side of the truck isn't going to be as good as an antenna mounted in the center of the ground plane (roof).

So does this just apply to CB radios or is this pretty much any kind of two-way radio on a vehicle? Cop cars having an antenna mounted to their trunk lid or up on the roof of their cars, doesn’t provide enough of a suitable ground plane?

Ground plane size is dictated by frequency. It ideally needs to be 1/4 wavelength in all directions under the antenna.
For public safety, a VHF high band antenna would want to see about 18" in all directions under the antenna. That's easily done on the roof of a vehicle. UHF wants 6". 800MHz wants 3". Trunk lids can be less than ideal, but there are other challenges when installing antennas that need to be taken into account. The mobile antenna on my truck is mounted dead center of the cab roof.

CB is challenging since 1/4 wavelength is 108". To have a 'perfect' groundplane under a CB antenna, you'd want an area 16 feet in diameter. Not an option on a road legal vehicle. So, we do the best we can with what we have. Mounting a CB antenna in the center of a truck roof is about the best option for mobile use. It is not perfect, but it is the best one can do, and it tends to work fairly well.

 

[mmckenna]

So I guess in order for this thing to make sense, the bottom part of my antenna mount that has the PL 259 connector on it would have to be in contact with that so-called ground plane and then on top of that, the part of my antenna mount that actually threads onto the base of the antenna would have to be isolated from this part we’re talking about, correct?

And it's no where big enough to provide a suitable groundplane for 11 meters. It's bling, pure and simple. If you want bling, it's a good option. If you want a ground plane, it's pretty much useless.

 

[corneileous]

Maybe.

However, I've discovered that there are those that want an antenna to look weird so it stands out or it suggests some sort of voodoo technology that magically makes a cheap add on make a radio work better. This sort of stuff is very common in the hobby side of radio, especially amateur radio. The more ugly/odd an antenna looks, the better it must work.
I seriously think I could make a lot of money by producing really ugly antennas and then writing a good B.S. explanation of why it works better than the competitor, without actually backing it up.

Not a dig at you, just pointing out that a lot of people view antennas as some sort of black magic that no one really understands, so odd/strange products get a lot of attention. In reality, the physics are pretty well understood, yet hobbyists don't want to put the effort/time into a good antenna installation, and would rather buy magic snake oil products that make them think they are getting something.

A properly tuned antenna on a good ground plane all properly installed will work better than snake oil add ons.



It's more about image, as I was suggesting above. With the physics involved, it's really hard to make an antenna stand out from the competition, so hobby oriented antenna manufacturers will turn to things like this to sell antennas/products.

I wouldn't spend money on that, but if it makes someone feel good about their radio setup, then good for them.



DC grounding and RF ground planes can be different things. Grounding your mirror bracket is good, but getting a well working setup when the antenna is mounted out at the end of a long arm sticking off the side of the truck isn't going to be as good as an antenna mounted in the center of the ground plane (roof).



Ground plane size is dictated by frequency. It ideally needs to be 1/4 wavelength in all directions under the antenna.
For public safety, a VHF high band antenna would want to see about 18" in all directions under the antenna. That's easily done on the roof of a vehicle. UHF wants 6". 800MHz wants 3". Trunk lids can be less than ideal, but there are other challenges when installing antennas that need to be taken into account. The mobile antenna on my truck is mounted dead center of the cab roof.

CB is challenging since 1/4 wavelength is 108". To have a 'perfect' groundplane under a CB antenna, you'd want an area 16 feet in diameter. Not an option on a road legal vehicle. So, we do the best we can with what we have. Mounting a CB antenna in the center of a truck roof is about the best option for mobile use. It is not perfect, but it is the best one can do, and it tends to work fairly well.

Thanks for that explanation. I had no idea that basically the higher the frequency, the smaller the ground-plane area has to be.

But with all this newfound information, I wonder if having a magnet mount antenna up on the roof of my truck would be better than traditionally having an antenna bolted to the mirror bracket? Next time I get a chance, I could take a look up on the roof to see if there is the typical NMO mount already there being that some of the trucks we have, depending on who had them before, have had those antenna bases already.

 

[corneileous]

And it's no where big enough to provide a suitable groundplane for 11 meters. It's bling, pure and simple. If you want bling, it's a good option. If you want a ground plane, it's pretty much useless.

I guess for the bling I could understand but I can’t understand why you’d want something like that anyway even in the name of bling if it’s gonna mess with your transmission/reception but then again, you get these guys with their antennas pushed forward who actually thinks that helps them…lol.

 

[ladn]

And it's no where big enough to provide a suitable groundplane for 11 meters.

A whopping 8.5"!

Remember to lube the threads liberally with snake oil !

 

[mmckenna]

But with all this newfound information, I wonder if having a magnet mount antenna up on the roof of my truck would be better than traditionally having an antenna bolted to the mirror bracket? Next time I get a chance, I could take a look up on the roof to see if there is the typical NMO mount already there being that some of the trucks we have, depending on who had them before, have had those antenna bases already.

It should work better if it is a metal roof. The ground plane needs to be conductive. If it's fiberglass, you need to put something under it.

 

[mmckenna]

I guess for the bling I could understand but I can’t understand why you’d want something like that anyway even in the name of bling if it’s gonna mess with your transmission/reception but then again, you get these guys with their antennas pushed forward who actually thinks that helps them…lol.

I have no idea. But search the scanner/ham antenna sales pages, and you'll find a lot of this sort of crap.

 

[corneileous]

It should work better if it is a metal roof. The ground plane needs to be conductive. If it's fiberglass, you need to put something under it.

Well I guess I’d just have to probe around with a magnet then to see if it’s metal and not fiberglass.

 

[mmckenna]

Or aluminum….

 

[corneileous]

Or aluminum….

Which would still be fine, correct?