Convince me to get a GMRS radio

[Tim]

I'm getting into radios lately, too. As I went down the rabbit hole I quickly realized the limitations of the JT with it's limited antenna mounting options. I do run a bed rack, though. I have no intentions of ever putting a RTT on so I am thinking of putting a piece of aluminum sheet metal on the rack to use as a ground plane. What sayeth the radio gurus on this plan? Have any advice on how to ground such a setup? My rack is aluminum but based on how the rack is mounted to the trail rails I would doubt there is good continuity to ground.

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[Radio Guy]

I'm getting into radios lately, too. As I went down the rabbit hole I quickly realized the limitations of the JT with it's limited antenna mounting options. I do run a bed rack, though. I have no intentions of ever putting a RTT on so I am thinking of putting a piece of aluminum sheet metal on the rack to use as a ground plane. What sayeth the radio gurus on this plan? Have any advice on how to ground such a setup? My rack is aluminum but based on how the rack is mounted to the trail rails I would doubt there is good continuity to ground.

For GMRS a 12" square or round piece of sheet metal is an adequate ground plane. For VHF like 2m or MURS about 3ft and for CB much more.

 

[Tim]

For GMRS a 12" square or round piece of sheet metal is an adequate ground plane. For VHF like 2m or MURS about 3ft and for CB much more.

Roger that. The NMO mount needs continuity to ground, electrically, correct? So if my rack doesn’t already have continuity to ground I will have to run a wire from the chassis to accomplish that? Sorry, I am sure this is basic stuff but I am just learning as I go.

 

[Radio Guy]

Roger that. The NMO mount needs continuity to ground, electrically, correct? So if my rack doesn’t already have continuity to ground I will have to run a wire from the chassis to accomplish that? Sorry, I am sure this is basic stuff but I am just learning as I go.

An antenna is only aware of the sheet metal ground plane below it and continuity back to the battery is irrelevant. If you had a GMRS whip on a 12" dia pie tin on the end of a broom stick, it would be happy.

For HF its a different story due to the longer wavelengths and you would want as much of the vehicle as possible to be the ground plane

 

[Tim]

An antenna is only aware of the sheet metal ground plane below it and continuity back to the battery is irrelevant. If you had a GMRS whip on a 12" dia pie tin on the end of a broom stick, it would be happy.

For HF its a different story due to the longer wavelengths and you would want as much of the vehicle as possible to be the ground plane

Thanks for the reply. For some reason I was under the impression that the NMO/coax needed to be electrically grounded. Right now I have a Midland 6db gain whip on a Cooltech cowl mount. It’s ok but I notice I have some ground loop interference when the squelch opens and I can hear other radio traffic. I think that is mostly related to my ground to the radio. I ran dedicated power/ground from the battery but after some research I believe it would be best to move the ground to the ground lug on the fender where the bonded jumper from the battery terminates.

 

[AKDrifter]

Thanks for the reply. For some reason I was under the impression that the NMO/coax needed to be electrically grounded.

The NMO mounts I've used that weren't magnetic all had the little bitey toothed thing to grip into whatever surface you mount them on. I will sand powdercoat and paint off where that thing bites to help with grounding, I've not had an issue at all. It does need some sort of ground plane. But as Radio Guy said, many a radio and antenna setup have been tested with pie pans and cookie sheets on the kitchen table.

 

[Radio Guy]

Thanks for the reply. For some reason I was under the impression that the NMO/coax needed to be electrically grounded. Right now I have a Midland 6db gain whip on a Cooltech cowl mount. It’s ok but I notice I have some ground loop interference when the squelch opens and I can hear other radio traffic. I think that is mostly related to my ground to the radio. I ran dedicated power/ground from the battery but after some research I believe it would be best to move the ground to the ground lug on the fender where the bonded jumper from the battery terminates.

Ground loops can cause electrical noise like alternator whine but not wrong radio traffic coming through a radio, that would be in the radio itself.

 

[Tim]

Ground loops can cause electrical noise like alternator whine but not wrong radio traffic coming through a radio, that would be in the radio itself.

That’s exactly what I have going on. The radio traffic is as expected albeit with some alternator whine and some “popcorn” in the background. Everything works. I just think I can improve my performance by altering the installation in a few areas.

 

[Radio Guy]

That’s exactly what I have going on. The radio traffic is as expected albeit with some alternator whine and some “popcorn” in the background. Everything works. I just think I can improve my performance by altering the installation in a few areas.

You should not have any alternator whine in a new JT and they don't have any spark plug noise that I have been able to detect, even on CB or amateur HF. I assume the noise goes away when the engine is off?

You can temporarily run the radio from a separate isolated battery to see if noise is coming in through the electrical system and power wires. That would be unusual in this vehicle and running power wires from the radio right to the battery will give the radio the cleanest power in the vehicle. I've run a number of radios off the AUX switched power with no problems and no noise.

Is your radio a remote head type with a main box that gets hidden and cable to a control head or display mic? If so sometimes a different ground point on the main radio chassis vs where the control head is grounded can create a ground loop and invite noises. I'd like to hear more about the install.

 

[Tim]

You should not have any alternator whine in a new JT and they don't have any spark plug noise that I have been able to detect, even on CB or amateur HF. I assume the noise goes away when the engine is off?

You can temporarily run the radio from a separate isolated battery to see if noise is coming in through the electrical system and power wires. That would be unusual in this vehicle and running power wires from the radio right to the battery will give the radio the cleanest power in the vehicle. I've run a number of radios off the AUX switched power with no problems and no noise.

Is your radio a remote head type with a main box that gets hidden and cable to a control head or display mic? If so sometimes a different ground point on the main radio chassis vs where the control head is grounded can create a ground loop and invite noises. I'd like to hear more about the install.

I have the Midland MXT275 so yes, the radio is hidden and I control and operate it from the mic. I have the main radio chassis up and to the left behind the glove box. The bracket is zip tied in place. I ran 12/2 wire through the grommet behind the glovebox and directly to the positive and negative terminals on the battery. The coax cable is routed under/behind the center stack and out the plastic grommet in the firewall on the driver's side. The coax is routed out between the cowl and the hood where it is mounted to the Cooltech cowl antenna mount. I have the Midland 6db gain 5/8th wave whip antenna. The coax is way too long so I have the excess bundled up and zip tied under the hood on the driver's side.

Close range transmissions are very good, like between my Wouxun kg905g HT and the JT. I definitely hear alternator whine any time the engine is running, though. It's pretty obvious as it changes with engine RPM and is super noticeable when the transmission shifts gears, like when starting an upgrade on the highway where it drops from 8th to 7th. I have also noticed the whine initiate when the Jeep starts after an auto stop/start event at a traffic light. I am 100% positive there is some sort or ground loop interference happening. I researched that and came across some pretty good posts on radioreference . com where it was explained in technical detail why it is better to run ground to the main grounding lug on the chassis and not directly to the battery. It may actually be a good idea to make sure the antenna mount is electrically grounded, as well. Apparently a difference in electrical potential can develop on the coax when things aren't grounded appropriately.

The easiest thing for me to do is move the ground to the chassis ground lug. I may run a jumper wire to ground the antenna mount or just use my fender mount. The cowl mount is a cleaner look for sure but this might be a case where function takes precedence over form. As I previously mentioned, I may fashion a ground plane out of sheet metal to mount to my bed rack. I will have to get a 1/2 wave antenna if that is the case as I don't want a 32" whip sticking up that high and banging off every low branch, parking garage, etc. as my rack is full cab height. It would also use up all that extra coax cable that is currently just bundled up.

 

[Radio Guy]

I have the Midland MXT275 so yes, the radio is hidden and I control and operate it from the mic. I have the main radio chassis up and to the left behind the glove box. The bracket is zip tied in place. I ran 12/2 wire through the grommet behind the glovebox and directly to the positive and negative terminals on the battery. The coax cable is routed under/behind the center stack and out the plastic grommet in the firewall on the driver's side. The coax is routed out between the cowl and the hood where it is mounted to the Cooltech cowl antenna mount. I have the Midland 6db gain 5/8th wave whip antenna. The coax is way too long so I have the excess bundled up and zip tied under the hood on the driver's side.

Close range transmissions are very good, like between my Wouxun kg905g HT and the JT. I definitely hear alternator whine any time the engine is running, though. It's pretty obvious as it changes with engine RPM and is super noticeable when the transmission shifts gears, like when starting an upgrade on the highway where it drops from 8th to 7th. I have also noticed the whine initiate when the Jeep starts after an auto stop/start event at a traffic light. I am 100% positive there is some sort or ground loop interference happening. I researched that and came across some pretty good posts on radioreference . com where it was explained in technical detail why it is better to run ground to the main grounding lug on the chassis and not directly to the battery. It may actually be a good idea to make sure the antenna mount is electrically grounded, as well. Apparently a difference in electrical potential can develop on the coax when things aren't grounded appropriately.

The easiest thing for me to do is move the ground to the chassis ground lug. I may run a jumper wire to ground the antenna mount or just use my fender mount. The cowl mount is a cleaner look for sure but this might be a case where function takes precedence over form. As I previously mentioned, I may fashion a ground plane out of sheet metal to mount to my bed rack. I will have to get a 1/2 wave antenna if that is the case as I don't want a 32" whip sticking up that high and banging off every low branch, parking garage, etc. as my rack is full cab height. It would also use up all that extra coax cable that is currently just bundled up.

Do others hear the alternator whine on your transmission or is it just on receive in your radio? You can do a quick test by moving just the ground wire from the battery to a nearby ground point under the hood for a test.

 

[Tim]

Do others hear the alternator whine on your transmission or is it just on receive in your radio? You can do a quick test by moving just the ground wire from the battery to a nearby ground point under the hood for a test.

I can’t answer that. I only noticed it while listening.

 

[Radio Guy]

I can’t answer that. I only noticed it while listening.

If you can get someone to receive your radio and there is no alternator noise on transmit then its more than likely a difference in ground potential between the radio chassis and remote control head. Is the radio bolted in its metal mount and the mount is screwed into sheet metal? Is the remote control head mounted where it grounds into sheet metal? That can be the makings of a ground loop.

If an alternator is worn out or has a bad diode it can make ripple on its output which can be heard as a whine in both in your speaker and your transmission.

 

[Tim]

If you can get someone to receive your radio and there is no alternator noise on transmit then its more than likely a difference in ground potential between the radio chassis and remote control head. Is the radio bolted in its metal mount and the mount is screwed into sheet metal? Is the remote control head mounted where it grounds into sheet metal? That can be the makings of a ground loop.

If an alternator is worn out or has a bad diode it can make ripple on its output which can be heard as a whine in both in your speaker and your transmission.

The radio is not bolted to anything at all. The mounting bracket is simply zip tied behind the glovebox and the radio is slid into the bracket as it normally would be. The radio is controlled from the mic, not a remote control head, so that is not bolted to anything either. The mic just hangs form a plastic mic holder type bracket that is double sided taped to the dash.

 

[Radio Guy]

The radio is not bolted to anything at all. The mounting bracket is simply zip tied behind the glovebox and the radio is slid into the bracket as it normally would be. The radio is controlled from the mic, not a remote control head, so that is not bolted to anything either. The mic just hangs form a plastic mic holder type bracket that is double sided taped to the dash.

Interesting. As I mentioned I've had several radios in and out of my JT fed from several power sources with zero alternator or spark plug noise. It could also be some radios are on the light side of input DC filtering and that radio is just more susceptible to any ripple on the DC input.

I also have a 100w police siren in the truck where I use its electronic horn sometimes and also patch my ham radio audio through it to an under hood speaker. These sirens are usually sensitive to alternator noise and I have not heard any.

If your truck were here I would stick a DC noise filter on it as a test and also temporarily swap the radio for a different type run from the same power leads. If the radio turns out to be very sensitive to DC ripple, a high current filter with choke input and a large bypass capacitance should fix it.

Anyone else on this thread with the exact same radio that can comment on alternator whine?

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