Antenna on a Fiberglass Airboat - Grounding Question

[firefighter331]

I'm a member of my local fire department, where we have this airboat equipped with a dual band radio. It may be hard to see in this picture, but the antenna is mounted toward the front, right in front of the cab.

Transmit quality is not great on it. Since it's a fiberglass boat and that obviously was the issue, the department bought a ground plane kit for it, which helped a little, but it still barely hits a repeater that's only 93 feet away.
My question is what if I run a wire from the circular part of the ground plane kit, and ground that to the battery. Will that help? My thinking is that it probably will, since all the metal on the back end is grounded to the battery, therefore it should give it a better ground plane and improve transmit quality, right?
Just my thinking on it. Please correct me if I'm wrong, and I'm open to whatever other suggestions you have for it.

 

[KevinC]

You need metal under the antenna for a ground plane, unless you have a "no ground plane" antenna (and this one doesn't appear to be one).

Even with no ground plane it should work farther than 93'. I would look elsewhere for a problem and rectify that first, then attack the ground plane issue.

 

[KevinC]

And please tell me that isn't a TRAM/Browning antenna. If so I'd suspect water migration through the spring if you didn't seal up the hole below the spring.

 

[cmdrwill]

equipped with a dual band radio

What frequencies are you using/needing?
And that antenna is NOT going to do any "dual band". Tram Browning, Comet Vomet Diamond junk.

 

[prcguy]

Even without a ground plane that antenna should hit a repeater many miles away. I think something else is wrong if it doesn't go 93ft. Put an antenna analyzer on it to see if its actually an antenna or something else.

For those types of installs I usually get some wide aluminum HVAC tape from Home Depot and make an X so each individual tape heading out from the mount is about 18" long for VHF hi band. Although that is a multiband antenna and probably a Browning. That tape is very wide like 3" and will make a fine ground plane. I put the tape on the underside of the fiberglass after the hole is cut but before the mount goes on so the mount bites into the tape for a good connection. Then slap a little gel coat over it or some other coating to seal against corrosion and peeling.

 

[WB9YBM]

Transmit quality is not great on it. Since it's a fiberglass boat and that obviously was the issue, the department bought a ground plane kit for it, which helped a little, but it still barely hits a repeater that's only 93 feet away.
My question is what if I run a wire from the circular part of the ground plane kit, and ground that to the battery.

A marine supply store that caters to the owners of fiberglass boats might be a good resource. As for running a ground from the battery, I'd suggest an alternative: run grounds to a common point near your radio to avoid "ground loops" (that's where ground wires are long enough to look like an antenna).

 

[kayn1n32008]

What two bands are you needing? You will have better results going with separate NGP antennas and combining them with a diplexer.

 

[iMONITOR]

How about mounting an antenna on the highest point of the propeller cage/guard? If might be a little directional but if you figure out in which direction you could point it to your advantage for the greatest range by maneuvering the boats position if necessary.

 

[firefighter331]

What frequencies are you using/needing?
And that antenna is NOT going to do any "dual band". Tram Browning, Comet Vomet Diamond junk.

I'm not sure exactly what the antenna is, but we have them on all the trucks as well. We mainly use these on 152.285, and they work great, but soon we'll be on this radio system operating in the 450 to 460 range.
No, it's not a cheap HAM antenna, it's an actual antenna designed for public safety - I just don't know exactly what it is.

 

[firefighter331]

How about mounting an antenna on the highest point of the propeller cage/guard? If might be a little directional but if you figure out in which direction you could point it to your advantage for the greatest range by maneuvering the boats position if necessary.

That's not an option due to clearance issues. There's one particular bridge they say the boat barely fits under, so we don't want to mount to a high point and end up dropping the antenna into the water/ice when we pass under the bridge.

 

[mmckenna]

This sort of looks like what I often see when a member of the fire department decides to "do it themselves to save money". No offense to the fire guys, but there are not many that are good radio guys.
I've had to fix a few...

I agree. Move that antenna and plug the hole. Whoever mounted it there needs to be taking out behind the barn.

Mount it up as high as you can. That'll improve range. Top of the fan shroud would probably be a good candidate. If not there, then consider using whatever is holding the canvas top up.

And if that is a Tram/Browning POS antenna, make sure it gets properly destroyed so someone doesn't try to reuse it and make your life hell again. I'd recommend killing it with fire, then running it over a few times with the heaviest truck you have access to. Then burn it again.

As others have said, I think you have bigger issues that just a crappy antenna/install location. If who ever installed that monstrosity did so without a ground plane, I'd suspect them of not using a 'thick mount' NMO, and it's entirely possible the center contact isn't touching.

 

[mmckenna]

I'm not sure exactly what the antenna is, but we have them on all the trucks as well. We mainly use these on 152.285, and they work great, but soon we'll be on this radio system operating in the 450 to 460 range.
No, it's not a cheap HAM antenna, it's an actual antenna designed for public safety - I just don't know exactly what it is.

If all you are using is VHF and UHF, then use a VHF/UHF dual band antenna.

https://www.theantennafarm.com/catalog/laird-technologies-c150-450cs-5582

 

[firefighter331]

I'd suspect them of not using a 'thick mount' NMO, and it's entirely possible the center contact isn't touching.

I did unscrew the antenna and bend the pin down a little, just to make sure that wasn't the problem. It didn't seem to affect anything. I also tried running a wire between the ground plane disc and the frame around the fan. That also made zero difference. I've been told that grounding it to the battery isn't practical due to possible interference with the engine.
I'm starting to think it's more than just the antenna. One of the lieutenants told me he bought one of those "no ground plane" antennas and that didn't work either.

I'm not sure what the right tool would be, but I'd like to test the amount of power I'm getting at the antenna to see if it's the full 45 watts. It's possible that the radio itself is the issue, or maybe a damaged antenna cable.

 

[KevinC]

Bending the pin down sure sounds like a TRAM/Browning antenna. That may not be your problem, but for something mission critical I should wouldn't rely on one.

 

[davidgcet]

first of all is the radio operating properly, you could have a bad radio or even poor power if it won't hit the repeater. switch to a direct channel and have someone take a hand held on the same direct channel a few hundred yards away or further, see if they talk to each other. if so then either the repeater channel is programmed wrong in the radio OR possibly you are simply too close. especially with VHF you can get receiver blanking, which is where the transmit radio signal is so strong it just shuts down the front end of the receiver on the repeater/nearby radio. I argued this with an ambulance service several years ago and I had to physically prove it with a yagi antenna and a spool of LMR to get it far enough away it didn't blank the repeater in the next room. they would often complain too about ambulances parked net to each other could not hear when one was talking but would hear dispatch just fine, I moved one ambulance about 50 feet and had them try it, whaddaya know everything worked. they still didn't believe me though...…………...

 

[mmckenna]

I did unscrew the antenna and bend the pin down a little, just to make sure that wasn't the problem. It didn't seem to affect anything.

Yeah, I suspect you have other issues. But I'd still not rule that out. Unless it's a thick mount NMO, it would be suspect.

I also tried running a wire between the ground plane disc and the frame around the fan. That also made zero difference. I've been told that grounding it to the battery isn't practical due to possible interference with the engine.

They are confusing DC ground with RF ground. They are not the same thing. Grounding the mount to the battery shouldn't make any difference at all. Same with the fan shroud. You need a metal ground plane under the antenna. There is no way to cheat that. Use the method PRCGUY mentioned above. I've done that on plastic ATV roof installs.

I'm starting to think it's more than just the antenna. One of the lieutenants told me he bought one of those "no ground plane" antennas and that didn't work either.

Yeah, at this point I'd say you have multiple issues to deal with. Since the rest of the install is questionable, I'd really start looking at the coaxial cable connector at the antenna. If the same person that installed the antenna installed the radio, I'd say the whole things needs to be looked at.
While I'm sure it's probably not one of the issues you are having, I'd also recommend taking a close look at the power wiring. Not trying to put anyone down, but there's a couple of red flags here with this install, and I suspect it's exceeded the experience level of the installer. If lives depend on that radio, it's worth every single penny to have a professional look it over. It's not working worth a dang right now, and it's absolutely not going to work when you are on a scene trying to save someones life.

I'm not sure what the right tool would be, but I'd like to test the amount of power I'm getting at the antenna to see if it's the full 45 watts. It's possible that the radio itself is the issue, or maybe a damaged antenna cable.

You want an RF watt meter. You'll also want an NMO to coax adapter to check the power coming out of the antenna mount. You won't see the whole 45 watts at the antenna mount, probably something a bit less than that since the coaxial cable will have some amount of loss.

I'd like to hear what you are finding with this. I suspect there's a number of issues that will need to be addressed:
NMO antenna base to NMO mount contact issue due to wrong NMO mount.
Likely either an improperly installed coaxial connector, or a crap load of coax all bundled up somewhere.
I'd also look at your power connections, grounding, and anything else.

I'd not trust this install.

 

[kayn1n32008]

I'm not sure exactly what the antenna is, but we have them on all the trucks as well. We mainly use these on 152.285, and they work great, but soon we'll be on this radio system operating in the 450 to 460 range.
No, it's not a cheap HAM antenna, it's an actual antenna designed for public safety - I just don't know exactly what it is.

Then I would suggest a VHF 1/2 wave, Larsen NMO-WB. On UHF I would suggest a Coliniear NGP. EMWave is another good company to deal with.

 

[cmdrwill]

a crap load of coax all bundled up

Maybe you will find the "coax all bundled up" all melted by engine heat.

Antenna suggestions need to be put on HOLD.

FIRST you need to get the NMO mount tested, then the coax cable.

 

[techman210]

I'm not sure what the right tool would be,

I would think at this point, it would be a service monitor attached to the radio.

 

[prcguy]

I don't see a problem with the mounting location, on boats you have to take into consideration things being moved on and off the boat and not taking out the antenna and its a soft top with no good place to get the antenna up high. You also want to keep the antenna away from the engine and spark plug noise. If they only need VHF and UHF into the far future a dual band Larsen would be an upgrade, otherwise that antenna works similar to a 1/4 wave on VHF and not sure about UHF.

That may be a PCTEL tri-band and those are supplied with some Motorola radios.

This sort of looks like what I often see when a member of the fire department decides to "do it themselves to save money". No offense to the fire guys, but there are not many that are good radio guys.
I've had to fix a few...

I agree. Move that antenna and plug the hole. Whoever mounted it there needs to be taking out behind the barn.

Mount it up as high as you can. That'll improve range. Top of the fan shroud would probably be a good candidate. If not there, then consider using whatever is holding the canvas top up.

And if that is a Tram/Browning POS antenna, make sure it gets properly destroyed so someone doesn't try to reuse it and make your life hell again. I'd recommend killing it with fire, then running it over a few times with the heaviest truck you have access to. Then burn it again.

As others have said, I think you have bigger issues that just a crappy antenna/install location. If who ever installed that monstrosity did so without a ground plane, I'd suspect them of not using a 'thick mount' NMO, and it's entirely possible the center contact isn't touching.