A real easy way to tell if the interference is in the power leads or the antenna is to disconnect the antenna while you are experiencing the interference. Crank down the squelch, crank up the volume and disconnect the antenna. If you still hear the interference, you know it is most likely in your power leads. If it goes away, the antenna lead is the culprit.

 

CHPMustang - I may have to give that mini coax a try

redford - great idea, I'll do that

 

Well redford... I just went outside and tried it. Seems like it's the antenna. I guess I need to route the cable better so it's not by so many wires? It's mostly under the dash above the pedals... lotta crap under there.

And...... The extra 2 ft of cable was tucked up under the dash zip tied to plenty of wires.... I cut the ties, brought the slack down and tucked it carefully under the carpet up towards the firewall. I tried it again and I got the same result.... as I turn up the AC the interference get worse. As I turn down the AC it gets less, and on the lowest setting the interference is barely there... ???

 

Ah the ubiquitous interference problems.

A couple thoughts -

If that antenna is new the coax should be "decent". As long as the antenna is matched well enough (less than 2:1 SWR, but as low as you can get it is better) you should be OK.

My method of testing SWR is to sweep a particular band (in this case the CB band). You want to see where the SWR dip is. From there you can adjust the whip. Lengthen to move the dip to a lower frequency, shorten to move the dip to a higher frequency. On CB I like to be resonant at channel 19.

Antennas with a direct ground to metal work better. The 3/8"x24 thread mounts are good for this. There are some hood/lip style mounts you can use also. I have my VHF/UHF antenna on one on the drivers side hood and it works great. My SUV has one on the top of the hatchback and works great. You don't have to drill holes to get a grounded connection.

If I am understanding the installation correctly the power wires are PARALLELING the factory harness through the firewall. That should be no problem - I have done the same with no problems, though my supply wires for my 12v accessories run through the body/chassis bolt access under the drivers side floor vs. going back out the firewall (a lot more space to work with).

On the topic of power wires - someone suggested running coaxial cable for the power wires. I have tried this and it was pretty worthless. It was even problematic after a while. I grounded the shields (coax for both the + and - runs direct to the battery, with circuit breakers at the battery side). What ended up happening is the + side ended up arcing where the ground braid connected up, it wasn't like "sparks" arcing but there was current flowing between them - enough that I could hear it buzzing. Moral of the story - shielded power wires is not really worth it.

Seal all connections well - coax, power, grounds. This doesn't just mean wrap with tape. Use some sealant. My favorite is CoaxSeal but I have used PlastiDip (liquid tool handle dip) before also. 3M super 33+ is my go-to electrical tape. The best method I have used is to wrap connections with a layer of tape BACKWARDS (sticky side out), a layer of coax seal, then a wrap of electric tape normal way (sicky side down).

On to the interference:

There are a lot of things that can cause interference. Motors, solenoids, injectors, spark plugs, distributors (older vehicles here), COP's (coil-on-plug), fuel pumps, etc, etc. It can be a pain to track down what specifically is causing the problem - and it may not end up being what you had diagnosed as the probable root.

On super duties there has been a notorious issue with fuel pumps. A buddy of mine used to build ambulences on SD chassis and there was even a kit that Ford had to address the issue for such service vehicles. I don't recall what the kit number was, but some research should lend some results there.

All root causes of interference aside - something to keep in mind is that grounding/bonding as much metal as you can in a mobile radio installation is key to good performance. Just because the body is bolted to the frame and the bed is bolted to the frame doesn't mean everything has a good RF ground.

My reference here for grounding is a mobile install (if you get in to "grounding" it is a very complex topic between lighting, safety, power, RF, antennas, etc). The difference between an RF ground and an electrical ground is that an RF ground is very low impedance. Another way to think about it is "low resistance". The rule of thumb here is grounding material should be wide and flat, ie - an 18 gauge wire isn't going to work well as an RF ground. If you open up your hood and take a look at the big braid grounds that are around the engine and bolted to the firewall or frame - this is what I'm talking about. Flat braid, strapping, flashing, etc all make good grounding material. I personally use 1/2" tinned copper braid. Bigger is better, the 1/2" is just what I have had from an old project so I've used it.

I have had mobile shortwave/HF ham radio set ups for 11-12 years (CB happens to fall on the high frequency side of the HF spectrum - between the 10 and 12 meter ham bands). In that time I have had my share of problems. Most of them I never identified except for the spark plugs on my 2003 Chevy silverado I had. I went through the trouble of getting copper flashing and shielding the spark plug wires, then grounding the shields I made. This was a LOT of wasted effort and time.

At one point somewhere along the lines in my researching of RFI in mobile installs I came across a very important tip:

Ground the exhaust pipe.

The theory here is that any RFI generated at the engine is free to radiate off the exhaust pipe - it is an antenna hanging under your vehicle. Most of the time the exhaust pipes are insulated on their hangers with shock isolators (plastic/rubber) to keep them from rattling. This also keeps them well electrically insulated from the rest of the vehicle. The end of the exhaust pipe is no longer at the same electrical potential as where it connects up to the headers on the engine. The RFI generated there (at the engine), whether it be injectors, spark plugs, alternator, etc, is free to radiate off the "antenna" that you may see as already being "grounded" to the engine through the headers.

As soon as you ground out the exhaust pipe at the rear of the vehicle you are bringing that end of the "antenna" to the same electrical potential, or very close, as what the frame is. That takes out the radiating properties and the RFI is dissipated.

The exhaust pipe ground took the spark plug noise on my 2003 silverado down from S9+ to about S2. In fact, at that point, the noise in there was a combination of all the other electrical things on the truck. It was very manageable. In my current truck with the filtering on my HF radio the signal meter barely moves.

Last thoughts for now:

Start with grounding/bonding. My method is to bond the bed and cab together. I do one strap on both sides. Ground the exhaust pipe to the frame. Maybe even ground the bed to the frame. Check all the grounds in the engine compartment - are any corroded off? Replace with good quality materials. Ground your radio to the vehicle. If your mount is bolted somehow to metal you should be OK, if not take a wire of some kind, or small braid, and directly ground the chassis of the radio to metal (seat frame bolt, etc). That should help tremendously.

 

KC8QVO.... WOW.... thank you!

Let's see...

Yes, the power pass-through wires are parallel to the factory harness through the firewall. I then ran the wires along the plastic cowl above the engine below the wipers.... and they come down along the passenger side fender and then to the battery. They are wrapped in loom for most of the way... overall they are protected pretty well and look neat and clean.

I like your idea of grounding straight from the CB to metal. I'm gonna try that... along with checking other grounds like you said.

I might ground the exhaust too, interesting idea... we'll see how it goes.

Thanks a bunch, I'll tackle this throughout the weekend when I have some free time. I'll report back!

 

Another thought regarding that exhaust pipe grounding - You probably won't want to tap the pipe itself. If you can use one of the hangers that is welded to the pipe as a connection point I'd do that.

The reason I bring this up is the first ground I put on my silverado's exhaust was straight to the pipe. I drilled a hole and used a self-tapping screw (I'll get to this below). I used the 1/2" braid for this also. All the tips of the braid I solder so they are easier to work with - I drill a hole and this is what the screw grips. Exhaust pipes have a unique tendency to get HOT. After about 300 miles in to a 900 mile trip home the noise level on my radio went WAY up. I thought it was power line noise but I couldn't get away from it. I was trying different frequencies trying to find where the noise was, but it was everywhere. I'm not sure why I didn't think to check the exhaust pipe, but when we stopped for the night it hit me to check that... sure enough the braid had corroded at the pipe and was flapping in the wind. That was one fix I wasn't going to do while on the road, I waited until I got home to fix it.

Self tapping screws - I use all stainless #8 or #6 hex head screws from ACE hardware with star washers. Always pilot drill them - with a bit the same size or slightly smaller than the drill tip so the threads will catch. The washers have the rough part on the outside and a smooth inside bore, vs. the rough inside and smooth outside. This star washer "bites" through the base and the braid for a better connection (think paint or rust here - the star points will get to metal).

 

Didn't want to quote that whole thing but some GREAT info there, thanks!!!

I have a single 4' firestik II attached to my Cobra 29LX and have been very unimpressed with the output distance.

I figured it to be a bad ground so I had no ground plane and ran a wire from the mount to the chassis. Yep, I used 12ga AWG wire. It didn't improve anything and now I know why!!!

I have it attached - clamped - to my Back Rack and I am sure it is not getting a ground through the paint. The rack is bolted through the pocket holes - all of which have paint as well.

This is why I tried the grounding strap. I am to the point where I was going to abandon the single whip and switch to dual whips as one of those acts as the ground plane.

I am about to reconnect my CB (I just built an overhead console for this - there is a thread on here) and have been thinking about how I will address this. Looks like I need to get some good grounding straps and start installing!!!

Now I need to reread that post b/c there is a lot of info there!!

Thanks KC8QVO!!

 

Absolute gold, KC8QVO! 73's de KI6JLX

 

I haven't had a chance to tackle my CB yet... got side-tracked and pretty busy this weekend. I'll try to dig into it today after work. Stay tuned...

 

update....

Haven't done much so far, but.... I ran a ground wire from the CB to metal under the dash. I turned the key to ON but did not start the truck. I then turned the CB on and the A/C on, and I'm still getting interference from the A/C. It's better than before but it's still there. Gonna keep working at it....

 

Good to hear you're working at it. That is the key. I can't make your interference go away from the other side of the computer but if I can offer some direction, the mental tools and resources, to go and try some things then I did good.

Another note - in your grounding quest - if you try one ground and it doesn't seem to "work"...

DONT REMOVE IT.

The more grounding the better off you are. Its just that some grounds may have a greater affect on killing noise than others. It is also entirely possible that no matter what you do you can't seem to kill it.

You know, another thought...

You can distinguish between "conducted" and "radiated" RFI pretty easy. If you power up your radio outside of the truck, from another 12v source, and another antenna or your current one removed from the truck but close to it, and you still have the interference then it is "radiated" (travels just like radio signals do). If it goes away then it is "conducted" (travels through wires or the ground connections).

The difference is conducted interference can be more difficult to solve as the "emitting" device is free to cause havoc regardless of grounding. In grounding it brings everything closer to the same potential and is a clear path to conduct. RFI is always some form of dirty AC or pulse. Cleaner DC will never create the same kind of RFI problem. What causes that AC or pulse can be bad contacts (small arcing), some kind of device out of spec/going bad that creates an abnormal oscillation, etc. If there is an arc - get a better connection. Clean contacts, replace connectors, etc. If a part is going bad (worn out brushes on a motor for example) then replace the part. If there is a computer that operates at some frequency and the circuitry breaks down the operation of the computer may very well appear to function "normal", in that it is doing what it is supposed to, but since the circuitry that runs it is "weak" the oscillation can become excessive, dirty, and/or the impedances are thrown off (like your CB with a high SWR and/or bad antenna ground - keep in mind your radio can cause RFI just as easy as other devices causing RFI to your radio).

If RFI is conducted and grounding doesn't take care of it then the solution would be ferrite beads or DC filtering on the power leads to suspect devices. The kit from Ford that I mentioned is essentially to add filtering on the in-tank fuel pump (a motor). I would not, however, put much faith in to DC line filters like what you get at Radio Shack. That is one area I won't proclaim to know much about - I haven't used any filters like that yet.

Here is another source that has a ton of information. The author can be a bit biased on some things, but overall it is a good resource - he also talks about the exhaust system grounding in a few places now that I found. It is fresh too - updated in April (some stuff you read online has been there for a decade).
K0BG

 

Thanks again for the great advice KC8QVO

I'm learning as I go here, and everything little thing I tweak seems to get me closer so I'm getting there

 

When you mention turning up the AC, I assume you mean the fan, not the temperature setting.

If you followed KC8QVO's suggestions you know if the problem is Radiated RF or Conducted RF. If it is conducted RF, he gave you the solutions. Assuming that the problem is radiated RF, not conducted RF and it increases with the AC setting, that RF is almost certainly coming from the AC fan and most of it is being radiated from the wiring for the fan acting as an antenna on the fan.

Pick up a power line interference filter. Put the filter on the power line going to the Heater/AC fan, as close to the fan as possible). You can get two and also put one on the input to the radio, but if the problem is radiated RF getting in through the antenna, the filter needs to be where it will stop the RF from getting radiated.

 

Yes, the fan.

I may give that filter a try... I've been sick the last couple days, but I'll probably play around with it again this weekend.

Also... if I adjust the squelch on the CB I can get the interference to go away and everything is quiet. So...... maybe it's not as bad as I think, but there's definitely interference.

 

A couple thoughts.

Is the fan noise isolated to when the A/C is running? Or if you turn the A/C off and just run the fan do you still get the noise?

Secondly - the squelch. If you look at the signal meter (I am assuming it is an analog needle) what the squelch does is it cuts the audio of the receiver below a certain level so you don't get all that white noise (the SHHHHHHHHHHHHHHHHHH you hear with the squelch open). If you have a buddy key up his radio at a certain distance, say a couple miles away, so your radio's needle is a steady peak, you can see where the squelch cuts off the receiver. Now move in to a mile apart and do the same thing. Your buddy's radio signal will be stronger and therefore will be above the "bar" you set with your squelch. So yes, you are entirely correct - if you crank the squelch up it IS going to quiet down the receiver by cutting the audio. However, what you did in the same process is made all the weaker signals (other CB users) you want to hear disappear - their signal levels may very well be below the level that the interference is and therefore the cranked up squelch closes them out. It would be like setting your squelch for your buddy at 1 mile and then try to go back to 2 miles - he's not going to get through. Your best bet is still to cut the noise out from the source.