Can gmrs and cb share power supply?

[ryanorr280]

I installed my mxt275 gmrs as well as cobra 75 cb under my console, both controllers near each other. I ran a single power supply to both radios from a free slot in the fuse block, using a fuse tap. Then grounded them at a bolt holding the park break mechanism in place.

I also have both antennas mounted on the rear crossbar of my roof, about 10 inches apart, one coax down each side of the car. With a grounding wire ran from a bolt on the cb antenna bracket to ensure the crossbar is grounded. (I have Thule pro bars that are aluminum)

if having both systems on, my gmrs will freeze when I key up my cb mic. I have to pull the fuse to kill power supply, then it will reset (power is not switched by ignition, it is 12v hot at all times)

Both systems appear to work fine, other than if I key up on my cb then my gmrs will freeze/lock up. Has anyone else had similar issues?

I’m assuming it’s my single power supply, will likely change that to test after the weekend but wondered if anyone else has seen this issue.

 

[ryanorr280]

Antennas are 3’ Firestick and midland 6db gain if that matters at all. My other thought was maybe it was catching antenna interference.

 

[ryanorr280]

 

[J.W.]

The volts won't be a problem but I bet the amps won't be enough on that fuse. Separate the power supply and see if that fixes the problem. You are probably getting some line bleed from the CB which could mess up your other radio.

 

[slomatt]

Can you provide some details on how your GMRS "freezes up"? Do all the buttons stop working? Does the display show something weird?

Most radio manufacturers recommend running the positive and negative wires directly to the battery, with appropriately sized fuses on both the positive and negative wires. The fuse on the negative wire is important because if the main ground wire on the battery is removed you still have a ground path through the shield on the coax, to the radio, to the battery and you need to protect that path from over current.

10 inches separation may not be enough for the two antennas and they are likely interfering with each other. Here is some information on spacing.

CB and Ham Mobile Antenna Separation Distance?

I have a 3” Firestik CB antenna on the back of my Jeep and I run a normal 4 watt CB radio. I need to mount a 39” Diamond NR-770H dual band Ham antenna...

forums.qrz.com

 

[Ubiety]

Separating power would be an “easy“ first step to learn more about what is going on; maybe try powering them from completely different sources and see what happens to the issue. As I read your post I keep thinking interference like @J.W. mentioned and would look there sooner than later. I’d try moving the antennas as well, especially up/down/vertically so that they are not at the same height (think of a big antenna mast with antennas separated vertically as you go up the pole). Do you have a separate mag mount antenna that you could hook to one radio and move around? I’d try different antenna(s) if you can.

Edit. I took @J.W.’s line bleed comment as referring to RF interference, upon re-reading he may not have been meaning that at all ;)

 

[ryanorr280]

Thanks for the advice guys.

as far as a better description, the gmrs screen shows the channel, but does not respond to any buttons including the power button.

I will split power/grounds next week. then if that doesn’t help it sounds like I may have to move the gmrs antenna up front somewhere

 

[ryanorr280]

Separating power would be an “easy“ first step to learn more about what is going on; maybe try powering them from completely different sources and see what happens to the issue. As I read your post I keep thinking interference like @J.W. mentioned and would look there sooner than later. I’d try moving the antennas as well, especially up/down/vertically so that they are not at the same height (think of a big antenna mast with antennas separated vertically as you go up the pole). Do you have a separate mag mount antenna that you could hook to one radio and move around? I’d try different antenna(s) if you can.

I do have a shorter nmo as Well as a couple mag mount gmrs antennas.

I may order a hood mount and move the gmrs up there. I went up high for range, but that would space me apart as well as put them at different heights.

 

[Ubiety]

Try one change at a time, test it and move to the next if necessary. But you probably know that ;)

Spent several evenings in Jeep last month with mag mounts, HT’s, etc. troubleshooting a problem with the jeeps ham radio. After a few iterations it became clear who the culprit was. Now with new antenna coax (and antenna) everything is great again.

 

[Ubiety]

Sounds like you are on the right track! To clarify none of my suggestions are around how you should do things for daily driving, rather a series of single-change experiments to narrow down the culprit. Once you know the culprit then figure out the correct mitigation for daily use.

 

[Sparksalot]

I installed my mxt275 gmrs as well as cobra 75 cb under my console, both controllers near each other. I ran a single power supply to both radios from a free slot in the fuse block, using a fuse tap. Then grounded them at a bolt holding the park break mechanism in place.

I also have both antennas mounted on the rear crossbar of my roof, about 10 inches apart, one coax down each side of the car. With a grounding wire ran from a bolt on the cb antenna bracket to ensure the crossbar is grounded. (I have Thule pro bars that are aluminum)

if having both systems on, my gmrs will freeze when I key up my cb mic. I have to pull the fuse to kill power supply, then it will reset (power is not switched by ignition, it is 12v hot at all times)

Both systems appear to work fine, other than if I key up on my cb then my gmrs will freeze/lock up. Has anyone else had similar issues?

I’m assuming it’s my single power supply, will likely change that to test after the weekend but wondered if anyone else has seen this issue.

Your antennas are too close together. Transmit on one radio is overloading the receiver front end on the other. Ideally they need to be as fas apart as possible. That's hard in a mobile condition. Try separating the antennas by 3 feet, and see what happens.

 

[ryanorr280]

Your antennas are too close together. Transmit on one radio is overloading the receiver front end on the other. Ideally they need to be as fas apart as possible. That's hard in a mobile condition. Try separating the antennas by 3 feet, and see what happens.

That’s the direction that I am headed after all the great advice, and research this morning. I think for the weekend, I am going to move them apart by sliding my mounts out to the edge of the cross bars to see if it helps, then order the mount midland sells that takes my GMRS to the LH hood bracket that should give me some distance apart, as well as a height difference. Plus, it will stil let me have them useable with the kayaks on the roof.

 

[ryanorr280]

i have confirmed that I do have antenna interference.

I did a little playing with it this morning I moved the antennas as far apart on the crossbar as possible. With them at each side, it no longer freezes up the GMRS, but I do now see signal show up on the screen of it while the cb is keyed up. I swapped to my smaller GMRS antenna with no real change from that.

I put my UT72 mag mount antenna from my btech handheld on the hood near the driver A-pillar and have no interference. Also placed it in center of roof on front cross bar with no interference. Now my debate is to mount my GMRS permanently of the fender or front crossbar on roof. I think to fight interference the fender is my safest location. Then leave the coax run to the roof and be able to easily connect it and turn off the cb if I need the extra height at any time.

Unless the thought of having a higher mount is pointless. My coax is ran already is the only reason I’m thinking of leaving it...

 

[ryanorr280]

I can’t get the one photo to flip right on my phone. But this is where they first were, and where they currently are spread farther apart.

 

[Ubiety]

Nice! Here is a question, will you be powering/using both radios together or only one at a time? Wondering if this will be an issue for you in real life (outside of testing to see if your install all works).

 

[ryanorr280]

Nice! Here is a question, will you be powering/using both radios together or only one at a time? Wondering if this will be an issue for you in real life (outside of testing to see if your install all works).

You know that’s a question that I am honestly asking myself.

I truly have no “need” for either daily. Simply put them in for SHTF moments or trail comms. GMRS more so to be able to talk to walkies at the lake if someone takes the kayak out/goes for a walk

so I theoretically could just leave it and use only the one needed at the moment I suppose.

i do like roof mounting. height is king.

 

[1Louder]

As you add more and more stuff to your vehicle I would suggest putting in a Bluesea Fuseblock and then running all of your things off of that. I have one mounted to the Firewall of my FJ with 4awg wire going to the battery. My 3 radios are connected to this fuseblock as well as my refrigerator and a few power ports. At the battery I have a kill switch. It just makes life easier than having a bunch of add-a-circuits. Nothing is "key controlled" so you have to remember to turn things off. That might be the only disadvantage.

Even with things fused I wouldn't split a wire to power 2 radios.

 

[J.W.]

@J.W.’s line bleed comment as referring to RF interference, upon re-reading he may not have been meaning that at all ;)

My bad, it was late and I now realize how terribly vague that was. Two separate issues I was addressing. 1) the need to use separate power, ie two separate fuse block points to power the two radios. Like @Greg Eigsti mentions, putting two hot wires from two different radios into the same fuse tap is going to cause a problem (at some point) it you turn them both on together. 2) Then there is the RF issue, CB radio antennas are not very efficient and being that close you will get a lot of interference. It looks like you have already run it down.

Like you say, if you only power on 1 radio at a time, none of this will likely ever be an issue, but it’s always good to plan for the unexpected and run these gremlins down before they show up out on an adventure.

 

[ryanorr280]

My bad, it was late and I now realize how terribly vague that was. Two separate issues I was addressing. 1) the need to use separate power, ie two separate fuse block points to power the two radios. Like @Greg Eigsti mentions, putting two hot wires from two different radios into the same fuse tap is going to cause a problem (at some point) it you turn them both on together. 2) Then there is the RF issue, CB radio antennas are not very efficient and being that close you will get a lot of interference. It looks like you have already run it down.

Like you say, if you only power on 1 radio at a time, none of this will likely ever be an issue, but it’s always good to plan for the unexpected and run these gremlins down before they show up out on an adventure.

i agree totally on that. I didn’t think about it the night I ran power wires though. One radio at a time until a secondary fuse block will be my safety measure for now.

As you add more and more stuff to your vehicle I would suggest putting in a Bluesea Fuseblock and then running all of your things off of that. I have one mounted to the Firewall of my FJ with 4awg wire going to the battery. My 3 radios are connected to this fuseblock as well as my refrigerator and a few power ports. At the battery I have a kill switch. It just makes life easier than having a bunch of add-a-circuits. Nothing is "key controlled" so you have to remember to turn things off. That might be the only disadvantage.

Even with things fused I wouldn't split a wire to power 2 radios.

that’s actually my plan. As well as secondary battery to power it all. Just haven’t gotten there yet, lol

 

[Sparksalot]

i have confirmed that I do have antenna interference.

I did a little playing with it this morning I moved the antennas as far apart on the crossbar as possible. With them at each side, it no longer freezes up the GMRS, but I do now see signal show up on the screen of it while the cb is keyed up. I swapped to my smaller GMRS antenna with no real change from that.

I put my UT72 mag mount antenna from my btech handheld on the hood near the driver A-pillar and have no interference. Also placed it in center of roof on front cross bar with no interference. Now my debate is to mount my GMRS permanently of the fender or front crossbar on roof. I think to fight interference the fender is my safest location. Then leave the coax run to the roof and be able to easily connect it and turn off the cb if I need the extra height at any time.

Unless the thought of having a higher mount is pointless. My coax is ran already is the only reason I’m thinking of leaving it...

Leave the coax in place. you can use it when you can your ham ticket.