Turbo Boost causes CB buzz

[JamaicaJoe]

Wasn’t questioning that, just trying to figure out your logic for VSWR. That measurement has very little bearing on the OP’s issue.

Actually it could if the shield on the coax is damaged near the radio or the antenna is a magnet mount and has poor RF ground where mounted. The VSWR may be very high and the coax is acting as an antenna to conduct common mode noise directly into the receiver. Now you have gone and scared the OP away and we will never know. Or maybe he is testing those things right now. 90% of the CB radio complaints are crummy antenna installations, the others have to do with the DC wiring. Been doing this since 1970's.

 

[cmc3]

OK, Well there is no such thing as a Turbo Boost Pump...Just saying.

After a bit of investigation, you are correct. There is no electrical boost pump. I did find a electrically operated, "Turbocharger bypass valve."

 

[cmc3]

Actually it could if the shield on the coax is damaged near the radio or the antenna is a magnet mount and has poor RF ground where mounted. The VSWR may be very high and the coax is acting as an antenna to conduct common mode noise directly into the receiver. Now you have gone and scared the OP away and we will never know. Or maybe he is testing those things right now. 90% of the CB radio complaints are crummy antenna installations, the others have to do with the DC wiring. Been doing this since 1970's.

This could be it. I drilled a hole in the roof. The coax ground to the roof metal may have gotten flakey. I need to rework the antenna anyway. It has intermittent VSWR problems. Dry <1.4, wet >2.5 sometimes driving it changes.

 

[Yosemite Sam]

What does VSWR have to do with this? As long as the antenna line is not running parallel to a power line and insulated properly, it should not be part of this issue…

 

[Yosemite Sam]

After a bit of investigation, you are correct. There is no electrical boost pump. I did find a electrically operated, "Turbocharger bypass valve."

The first question(s) should be at what frequency is the noise being generated: Is it being received at the RF receive frequency (~27.00 MHz) or is it being heard at an audio frequency (20 Hz - 18,000 Hz).
To determine that, disconnect the antenna. Is the noise still prevalent? If it's gone then the noise is being generated at the receive frequency (~27.00 MHz). If the noise is still there, with the
antenna disconnected, then the noise is being generated at the audio
frequency (20 Hz - 18,000 Hz), in which case it's probably being
picked up on the power line (12VDC) in which case you should consider
bypass capacitors, chokes and definitely looking for bad grounds. In
the case of bad grounds it most likely would be loose or corroded
connections.
As far as VSWR is concerned, LokiWolf is absolutely correct; VSWR,
voltage standing wave ratio, is totally a function of a radio's
transmission ability and would have no bearing on the radio's
reception of noise, unless of course you're speaking of the affect
of a VSWR of 1 to infinity which would clearly be an indication of
no antenna connected to the radio!
As far as what's actually generating the noise you would have to
investigate what actually occurs when you engage the turbo boost on
your particular vehicle. "Something" is engaging electrically during
that sequence. Perhaps something to do with a change in the
transmission when it shifts into higher RPM's when you engage the
turbo boost?

Just my 2...and a half cents worth.

 

[LokiWolf]

After a bit of investigation, you are correct. There is no electrical boost pump. I did find a electrically operated, "Turbocharger bypass valve."

I knew I was correct, hence why I said it.

 

[LokiWolf]

Actually it could if the shield on the coax is damaged near the radio or the antenna is a magnet mount and has poor RF ground where mounted. The VSWR may be very high and the coax is acting as an antenna to conduct common mode noise directly into the receiver. Now you have gone and scared the OP away and we will never know. Or maybe he is testing those things right now. 90% of the CB radio complaints are crummy antenna installations, the others have to do with the DC wiring. Been doing this since 1970's.

Only been doing it since the 80's so you got me there, started when I was 10 helping my dad with his BaseStation CB, and HAM radios. Now I do modern RF(WiFi). I would put the 90/10 in the other direction. Most of the time when I help somebody it is CRAPPY wiring to the radio, and the antenna is not an issue. But either way we can agree, those are the causes.

 

[LokiWolf]

The first question(s) should be at what frequency is the noise being generated: Is it being received at the RF receive frequency (~27.00 MHz) or is it being heard at an audio frequency (20 Hz - 18,000 Hz).
To determine that, disconnect the antenna. Is the noise still prevalent? If it's gone then the noise is being generated at the receive frequency (~27.00 MHz). If the noise is still there, with the
antenna disconnected, then the noise is being generated at the audio
frequency (20 Hz - 18,000 Hz), in which case it's probably being
picked up on the power line (12VDC) in which case you should consider
bypass capacitors, chokes and definitely looking for bad grounds. In
the case of bad grounds it most likely would be loose or corroded
connections.
As far as VSWR is concerned, LokiWolf is absolutely correct; VSWR,
voltage standing wave ratio, is totally a function of a radio's
transmission ability and would have no bearing on the radio's
reception of noise, unless of course you're speaking of the affect
of a VSWR of 1 to infinity which would clearly be an indication of
no antenna connected to the radio!
As far as what's actually generating the noise you would have to
investigate what actually occurs when you engage the turbo boost on
your particular vehicle. "Something" is engaging electrically during
that sequence. Perhaps something to do with a change in the
transmission when it shifts into higher RPM's when you engage the
turbo boost?

Just my 2...and a half cents worth.

I would say that was worth WAY more than 2.5c! Thanks for picking up what I was putting down, and taking it MANY steps further.

Nothing that the "Turbo" is doing would generate electrical hum that would affect ANY radio. When the turbo is very "active", so is everything else, like RPM(Which means more electrical noise), because EVERYTHING involved with the engine Electrically is doing everything faster/stronger. The alternator is spinning faster, the plugs are firing WAY more, which means the coils are discharging more, the injectors are firing, MANY things.

@cmc3, sounds like you have MANY issues. SO many better ways to mount antenna's nowadays than drilling the roof, but I digress. Fix your grounding issues. Does the hum disappear if you change the wiring to the antenna with just a spare piece of cable? Have you verified a good ground at the radio itself? Does the hum happen if you just rev the motor without driving? Can you get a sound clip and post it? I can tell the frequency pretty quick, but you could do that with an app on your phone too.

 

[cmc3]

Thank's to all for the good suggestions. I think my next step will be to re-work my antenna mount to ensure good ground contact between the coax shield and car body at the mount point. Then use a spectrum analyzer to correlate noise with sources. The antenna is a loaded whip center mounted on the roof. When I installed it, I used a network analyzer to tune it. In the beginning I had better than 15dB return loss. But something seems to have changed. Possibly the ground has worked lose and become intermittent.

 

[JamaicaJoe]

Thank's to all for the good suggestions. I think my next step will be to re-work my antenna mount to ensure good ground contact between the coax shield and car body at the mount point. Then use a spectrum analyzer to correlate noise with sources. The antenna is a loaded whip center mounted on the roof. When I installed it, I used a network analyzer to tune it. In the beginning I had better than 15dB return loss. But something seems to have changed. Possibly the ground has worked lose and become intermittent.

If the antenna was tuned with one or more of the vehicle doors open and then checked later with doors closed, the tuning will change. Also if you have the vehicle near overhead wires, a garage door etc, the VSWR will be affected. At 27 MHz the wavelength is ~ 36 feet and within that distance anything can make an effect on the tuning, including yourself. If you have an old school analog ohmmeter with a needle, set it to lowest ohms scale and test the outer shell (part soldered/crimped to coax, not threaded loose nut) of the coax connector to the vehicle ground near roof. It should show much less than 1 ohm and should not vary when you move the coax and antenna whip around. If it does you have a loose connection in the shield or NMO mount. Do same from center pin to the antenna whip * or center button on the NMO mount. There should be continuity there as well. Now with antenna removed, check to make sure no continuity from center pin of coax to the outer shell. It should be infinite. For all tests, move stuff around while ensuring a good connection on the test points.

NMO mounts are designed to be installed with a special hole saw that takes a bit of paint off of the roof right around the hole. The mount itself should bite into the paint if tightened enough. But unless that electrical connection is made there may be resistance in that connection. The clamp on the bottom also makes a contact, but if there is paint or rust beneath, there may be a poor connection. Some bit of dielectric grease can provide a weather seal on the rubber O ring and brass to prevent rust from occurring.

* You may have to remove the antenna coil and whip. Some antennas have continuity from the whip to the center pin on the NMO . Some do not. Some may have continuity from the pin on the NMO mount to the outer threads for the NMO. These tests are directed at making sure your NMO mount and cable are intact and that the NMO mount has metal on metal contact at the roof sheet metal. If not, RF current and noise can travel the outer length of the coax and the noise can get into the receiver.