Base-Loaded CB antenna - antenna noise

[oft]

I am dealing with a problem where I am getting noise on my CB only when I cut on the AC, heat, defrost, or vent fan. Doesn't matter which selection I choose, the noise is present when the blower motor is on.

I was looking at the numerous threads on RR about troubleshooting the noise and tried the suggestions/solutions listed (installed an inline power filter to the B+ of the CB, checked grounding of the auto body, and tried the trick of a 0.1µF ceramic disc capacitor across the leads of the blower motor) with no luck eliminating my problem of noise. However, the solutions were helpful for me to finally able to determine that my noise issue is coming in from the antenna itself and not the incoming power wire.

I finally decided to google the topic and came across a forum where a guy had an issue of picking up noise only when he had to cut on his windshield-wipers and claimed that the only way he was able to solve the problem was to change out his fiberglass antenna (Wilson FGT or Firestik) and install a CB antenna that had a coil at the base of the antenna.

He claims that the center-loaded antennas will not work and that it has to be the base loaded antenna. His logic is that since the coil is at the bottom of the antenna (even though it's a part of the antenna) that the inline coil in the antenna will filter out noise from motors in the same mindset and mentality as those inline coil noise filter kits you install on the B+ wire going into the radio.

Does this make sense and is this true? I wanted to know before I take the gamble of purchasing a base-loaded coil antenna and swapping out my current fiberglass antenna.

Thanks for your help in advance.

 

[hhrj]

Tuned up any older vehicles lately? We always saved the capacitors and used them on alternators, blower motors, and electric fuel pumps. You can still buy them at any auto parts store. They would clear up the noise in about 90% of the cases. Attach the body of the capacitor under a motor screw and keep the lead short to the + wire.
YMMV.

Good Luck, Ron

 

[kb2vxa]

"Does this make sense and is this true?"

No, and no. The source of the noise is arcing motor brushes and since arcing is normal the only way to stop noise is to shunt it to ground at the source so it's not radiated by the wiring. I'm an old hand at this and hhrj is right, that's what those capacitors are made for. They even have a slotted mounting tab to go under the screw or nut that holds the end bell to the motor housing where the wire comes out. Oh, NEVER remove crew or nut or you'll have one heck of a problem, just back it off enough for the tab to fit.

Oh, if "Mr. Coil" actually believes himself I'm sure you can sell him a can of the famous Dr. DX's antenna wax guaranteed to make electrons slide faster and give you those coveted double naught to one swors.

 

[kruser]

In addition to installing a good working cap on the blower motor, have you checked your coax to your antenna?

Check the ends and make sure the connector is still tied to the shield braid of the coax at the radio end and at the antenna end.
The antenna end could be exposed and may have corroded. The radio end could have simply pulled or torn out of the PL259 plug from stress or vibration leaving just the center conductor attached. I've seen that a lot on the cheap crimped PL259 connector plugs that are fitted to pre-made antennas and pre-made coax lengths like Radioshack sells.
Also check the point where the cable enters the vehicle. I've seen a lot of them start to breakdown at that point especially when people just stick them in the rubber gasket area of a door to get them inside the vehicle.
After the door opens and closes on that cable a bunch of times, it will fail.
An open shield will allow all kinds of noise into your radio.

 

[kruser]

Oh, NEVER remove crew or nut or you'll have one heck of a problem.

I take it you have done this probably one time before:wink:

 

[frank-ortiz]

I have the same issue and have been dealing with it for months now, no matter what CB radio is in my car with my Wilson 5000 CB antenna. I get A/C noise into my CB radio as soon as I turn on the A/C, even wiper blade motor noise,I have changed the cables, connectors on the cables, I have tried using braided ground straps in my vehicle I have grounded the trunk of my vehicle, and after all of that work the noise is still there and never goes away. Does your radio have a noise blocker and a Noise limiter built in? If it does use it.

 

[LtDoc]

Noise.
You have a choice, stop the receiving device from receiving that noise, or 'clean' up the device producing the noise. That first choice isn't always possible for a number of reasons so the second choice is the 'best' one. The down side to that is that 'cleaning' up the noise producing device isn't always very easy, getting to the @#$ thing can be a real trick!
All noise is either AC or a 'pulse'. So, shunting/by-passing that AC/pulse to ground is the idea. Another is to stop that AC/pulse from getting any further away from that device through the power line feeding that device. That shunting/by-passing is usually done with capacitors, the 'stopping' of the noise through the power line is done with an inductance/coil. A combination of the two, inductance and capacitance, is also a very nice way of doing it. And then there's another way of 'curing' noise, which is by shielding the device producing the noise. Enclose the noise in a metal 'box' it can't get out of. That 'getting out of' the noise producing device is usually done by radiation. Wrap the @#$ thing in metal foil and then ground the foil. THAT can be very un-practical at times, so keep that in mind.
That's basically how you 'cure' noise problems of all sorts. The specifics of doing all that can get complicated.
Good luck!
- 'Doc

 

[oft]

I changed out the coax cable and put a new PL-259 on the end and no luck with reducing/eliminating the noise. I even tried routing the coax from the opposite side of the vehicle and no luck.

I'm going to try the capacitor trick this weekend.

I did not find an old ignition condenser around the house nor did the local auto parts stores have them in local stock but only had them available via special order. I decided to research ignition condensers online and discovered that people had taken capacitance meters and measured them and discovered that most condensers ranged anywhere from 0.47µF to 4.7µF and were not the polarized electrolytic type capacitors but literally tin foil plates with a wax paper dielectric. I looked around my house and found some ceramic or tantalum non-polarized capacitors of different values ranging from 0.47µF to 6.0µF all of them rated at 250 VDC that I am going to try.

I have an old computer power supply with some of those 16,000µF 35 WVDC electrolytic capacitors. I know they work well with DC filtering post rectifier but will they work with noise filtering?

 

[LtDoc]

The only thing I'd say to be careful with is the polarity of that electrolytic capacitor. Those sizes should make some difference. If the small ones don't do it, use the larger ones, or just parallel them.
- 'Doc

 

[oft]

Ding Ding Ding Ding Ding:

I had some daylight tonight to play around and experiment. I located the positive wire on the blower motor connector and was able to jam one lead of the tantalum capacitor into the connector and took the other lead of the tantalum capacitor to the front fender right beside the blower motor. I found that noise elimination started around 0.68µF and optimized between 2.7µF to 4.0 µF before somehow degradating again with increased capacitance 6.0µF and above.

I then tried the same process with the aluminum electrolytic capacitors starting with a 1.0 µF and increasing up to a 16,000µF and did not get as good of a result when compared to the tantalum capacitors. I now believe that the capacitor construction is also in play especially when others state that they used old ignition condensers which I found through research that they were literally tin foil plates with a wax paper dielectric.

This weekend, I will make the solution more permanent. and I thank everyone who contributed for their help.

--------

 

[kb2vxa]

"I now believe that the capacitor construction is also in play especially when others state that they used old ignition condensers which I found through research that they were literally tin foil plates with a wax paper dielectric."

You're on the right trail but first I don't understand why you tried electrolytics, they were never intended for arc suppression. That's the specific purpose of those old ignition caps, the value was never marked (it would only confuse mechanics) but it was chosen for optimum performance. Then the physical construction plays two parts, the body surrounds the cap for shielding and the ground tab short for a solid connection so the cap itself won't radiate. The second part is they're impervious to moisture, dirt and petroleum found in the engine compartment.

Ignition condensers, you called it right down to the old name, before capacitors they were called condensers. Condensed electricity? (;->) For the kids born too late to work on an old Kettering ignition system here's a simplified schematic to show you how it worked. My '57 Chevy was SO simple to work on. <sigh>

Oh before I forget the question much earlier, I worked on more car heaters than I care to remember. I found out early the bolts that hold the end bells on the motor go all the way through end to end so if you're not careful you have to take the motor off the blower to tighten it up again. Simple in old cars but today's are anything but mechanic friendly! <groan>

 

[oft]

kb2vxa:

The reason I tried an electrolytic was because I was thinking in terms of DC (since 12 VDC went to the blower motor) and filtering after rectification where increased µF would also increase filtering of ripple. After figuring out by trial and error and finally understand what was going on in the blower motor with arcing of the brushes backfeeding/radiating , I realized that it was acting more like transient high frequency AC.

Based on what you told me about the construction of the condensers plus the under the hood environment, I will probably end up getting a condenser with the metal clamp on order from the auto parts store (Advance Auto Parts said they can have it overnight) and go that route instead of using the tantalum cap I played with because of the 100°C / 212°F rating of the tantalum cap and with the high heat in the summertime, may eventually break down.

I will have to tap the positive lead with a line splice near the connector that mates to the blower motor. I did take the blower motor out and it has four bend tabs from the housing to the end bells with one spotweld holding the tab to the side of the motor. Why??????? I guess the modern age of disposability and to keep you from rebuilding the motor and replace the brushes.

When I became a teenager, most of the 10-15 year old used cars in my budget had already migrated over to the electronic ignition modules like GM H.E.I.. The only thing I now see points / condensers on now is old riding lawnmower engines and now when you get repair parts (because the condensers do degrade and decompose) are now retrofitting with these small quazi-electronic ignition boxes.