SPA gauge & CB Radio

[Cliffman]

I just installed my new Cobra CB radio and noticed that when I key up the mic the SPA gauge goes nuts. Hooked a SWR meter up to it and I'm getting good readings. Through my testing I found that if my SWR's are high the gauge's are not affected. Any body else having this problem?



Cliff

 

[EMDDIESEL]

Yet another reason why i hate digital gauges. Electrical interference.

 

[JR2]

Well I do not have a CB and I am an eletrical moron but here goes. Are the CB power and SPA power on the same circut?? Did you run your antenna wire up behind the gauge?

I think either one of these could cause a problem.

 

[RBrush]

It could also be RF interference. I have a similar problem with a temp guage I use in the winter at work. The power comes from the same power studs, and the sensor clips to the mirror near the antenna. Don't know if it is a power fluxuation or an RF problem. HHHMMMM, (scratching head)





Rich

 

[Cliffman]

JR, Good try but no dice. I used a 10-g wire that runs down through the floorboard under the lift-up console (that’s also where my CB is mounted) and down the frame to the starter. The ground wire is screwed to the floorboard where I attached the CB unit. The coax is also ran about 2" next to it. Again, down through the floor board and back towards the fuel tank and up the inside of the side bed of the drivers side, through a hole on the inside of the bed and into my 5th wheel tool box where the antenna is attached to the tool box. The SPA gauges are mounted on the piller and the hot wire comes directly off the fuse box.



Rich, It's undoubtedly RF interference. Some how the RF is getting into the gauges wire. The gauges are shielded, but I just don’t know enough about electronics to get this thing resolved It’s my guess that the hot or ground wire from the gauges is some how acting as an antenna and receiving the signal. But how the heck do you stop that from happening.

 

[frijole]

ME TOO

I've had the same problem for over a year. Talked to Mike Crossley, (bought my SPA gauges from him), and he said he would look into it. (that was at May Madness). Haven't heard from him on the issue. I've got a Ranger 6900, puts out a fair amount of wattage. I've tried isolation, changing ground location, shielding of all wiring etc, nothing seems to work to eliminate the interference. They use these gauges in Indy cars, which have upper end radios in them as well, soooo? I guess we need to call the Mfg and try them for an answer.

 

[BigDaddy]

Maybe this will help.

Cliffman,



Looping coax excess helps reduce RF interference. This is pretty much a gimme, but wanted to mention it.



How many gauges do you have and does it effect all of the gauges or just certain ones. If it is all, check the routing of the CB Coax cable. If it is only one gauge, check the routing of that harness in relation to the SPA harnesses.



RF interference is a strange thing. It can play havoc on unshielded wires and harnesses and can be transferred through the body.



Believe it or not, for our aircraft , all coaxial cable should be routed no closer than 12 inches to instrument wiring (keep in mind we run higher wattage radio’s, yet our gauges are low amperage, similar to the SPA’s).



An old trick is to shield the affected wiring with Tin Foil. It may not look pretty, but it works



Hope this helps.

 

[dabubba]

hey cliff- I've got a bombed ranger and It doesn't bother my spa- My antenna coax does not travel near my power for the cb- I bring the coax across the cab from the side of the cab under the drivers seat and the excess is coiled under the back seat-the power comes from the dash through the shifter/cup holder- this is the only differance between how our cb's are set up- in fact my cb and spa are coming off the same 12v tap-- hope this helps

 

[Cliffman]

dabubba,



My power wire and coax go in different directions also. Have you ever tested the SWR's on your CB? When we were coming back from MM I kinda had a hard time hearing you over the CB. When the SWR readings were high (3. 5) on my setup the gauges were only slightly affected, it's only when the SWR's are at there lowest (2) is when it's a problem. The lower the SWR's the worse the gauges get.





BigDaddy,



All gauges are affected, some more than others. I have 3 sets on the pillar, 1 EGT/Boost, 1 Pressure/Oil Temp and 1 Oil/Oil. The EGT side of the EGT/Boost gauge is the worst hit. When I key up the mic the EGT gauge goes from 60 to 1747 and the boost goes from 00 to 05 psi. On the Pressure/Temp gauge the pressure goes from 00 to 01 and the temp goes from 63 to 68 and on the Oil/Oil gauge the top oil temp goes from 58 to 54 and the bottom goes from 53 to 321 . What’s up with that? Why would the top half of the gauge hardly be affected and the bottom side be hit so hard I also have a 175 watt amp mounted next to the CB and when I power it on the gauges get worse. One other thing I should add, when I first installed the CB I coiled some excess coax under the seat, someone informed me that doing that was not good and the coiled up coax would act as an antenna and raise my SWR's, so I cut out the excess coax and the SPA gauges got worse.

 

[John]

ABSOLUTELY NO PROBLEM with interference between my SPA gauges and my ("Turbo tuned") CB although, both are on a different circuit of my Painless Wiring Cirkit Boss. In addition, the antenna wire is routed in such a way that it is almost never near any other power wires, and where it does it intersects same at right angles.



Cliffman, I would use a better ground. Personally, when I used to install trick audio equipment in previous 4x4s I learned that a good, common grounding point eliminated a lot of potential future problems. On my '98. 5 Ram there is a good factory ground (stud with nut... the nut uses a 10mm wrench) on the driver side just above the plastic kick panel. I believe there was only one factory ground wire attached there when I first installing accessories.



Also, it's OK to coil up the excess coax cable IF you fasten it together in the middle like a skein (looks like a figure 8). Coiling the excess in a series of loops MAY generate interference. The Firestik website explains this in great detail.

 

[Cliffman]

Hey John, Thanks for your suggestions. I spent another 2 hours d!cken with this thing today and still no change. Got my SWR's down below 2. 0 thanks to your suggestion regarding the coiled (figure 8) coax cable and know the gauges are worse . Correct me if I'm wrong, but with those SWR #s my ground should be fine. Its gota have something to do with the gauges or how there wired don’t’ ya think

 

[BigDaddy]

Status?

Cliffman,



Did you try the Tin Foil trick?



BTW, Where is your antenna located?

 

[Cliffman]

Haven't tried the tin foil trick yet. How do ya do it? Just wrap it around the hot and ground wires? My antenna is located on the back edge of my 5th wheel tool box, right behind the rear window and about 4" in from the drivers side edge of the tool box. For testing I barrowed a friends CB that plugs into the cigarette lighter and located the magnetic mount antenna on the roof of the truck so as to get a good "ground plane". The gauges were still affected but not as bad. The SWR's were about 2. 6:1. I’ve come to the conclusion that it's not the installation of the CB based on the fact that my SWR's are below 2. In order to get those kind of # the installation has to be good. The only thing I'm lacking is an excellent ground plane like the kind you get when you mount your antenna on the roof of the truck.

 

[BPINE]

Hey Cliff I would sugest you wrap he whole truck in tin foil, it is the wrong color anyway. lol

 

[BigDaddy]

Cliffman,



You said, "For testing I barrowed a friends CB that plugs into the cigarette lighter and located the magnetic mount antenna on the roof of the truck so as to get a good "ground plane". The gauges were still affected but not as bad. "



This is the key. You have already started to eliminate the EMI (Electromagnetic Interferance) by moving the antenna from the affected wiring/gauges. I would move the antenna to the right hand side of the truck and as far from the cab as you can.



The problem is the EMI on the small gage wires and insulation on the SPA wiring. They seem to be 20 ga. at best and only draw 16-48 mA. Plenty for their operation however, I would have used twisted pair, sheilded wire (Ron are you listening?). If you don't want to move the antenna try this first:



1. Wrap your power and ground wire together to get about 5 - 6 twist's per foot.

2. Wrap this harness with Tin Foil. No air gaps. Kinda like wrapping a wine bottle for xmas.

If this doesn't work go to Radio Shack and purchase some Ferite Beads.

3. Position the ferite beads about 3 or 4 per foot.



BTW, I am assuming that you have checked the grounds like John suggested. The SPA grounds also.

 

[Cliffman]

LOL at BPINE. Well, at least it would be appropriately colored Driftwood, tin foil silver, same thing

 

[John]

Hold on a sec...

Is the toolbox constructed of aluminum? And, would it even provide a quality ground plane? If so and it doesn't, you may want to try one of those CB antennas that DO NOT require a ground plane. I know Firestik has several different models of these... the coax is the ground plane. As you might suspect, the coax CANNOT be shortened/lengthened... the length is critical to its function.

 

[Cliffman]

John, That thought had accrued to me also, but with the low SWR's (below 2) that I'm getting, I’m assuming my ground plane is good enough. It might be worth a try though

 

[BPINE]

Hey Cliff I have some ferite beads I will bring some home.

 

[Cliffman]

Hell, I'll try any thing at this point. LOL