Alternator Whine Help Kenwood TK-790

[Q12]

Hello! I have alernator Whine issue on my Kenwood TK-790 Mobile Radio Setup.

The Vehicle Everything is in Is a Ford Expedition 2000.

I have it configured in a Dualband Setup with a TK-890. Both Radios Controlled with a Single Control Head.

The TK-790 Is Radio 2 in the setup and is Connected to a Kenwood Filter (KLF-2) and then to the Car battery with Fuses on both Positive and Negative.
Antenna Setup is an NMO with a Dualband Comet in the center of the roof.

Same thing with the 890 but a Magmount Antenna instead.

When I would Transmit on UHF with the 890 there is No Alternator Whine in my Transmission or Recieve Speaker.(It used to have it Untill I Ungrounded my Control Head and Problem Solved.)

But On the VHF Side, When I Transmit and Just receiving audio, I hear the whine and it correlates with my Engine RPM.

It goes away when I run the Car on Accessory Mode.

The 890 Is set-up with Ignition Sense and Gets the Ignition sense from the Control head with a Fused and Tapped Wire coming from the Fusebox.

https://imgur.com/a/w0vGugK

Things Ive Tried already.

-Disconnecting the Mag Mount Antenna to make sure it's not That that's causing the Ground Loop.

-Grounding the Radios to the Cars Chassis.

-Using a Magmount Antenna for the VHF Radio.

-Removing the Ground from the Control Cables of the Radio 1 to Radio 2

-Setting up my Base TK-790 in place of my Mobile and no Whine when this happens.

https://imgur.com/a/Wj7llH0

I'm guessing it has to do with the Control Cable to Radio 1 that is causing a Ground Loop.

Any Help is Appreciated!

 

[mmckenna]

I had something similar happen a long time ago.
I had run both the positive and negative power leads direct to the battery. It was plagued with alternator whine.

On most commercial radios, they'll instruct you to ground the negative power lead directly to the vehicle body as close to the radio as you can.
I'd recommend doing that with both radios. You should be able to ditch those KLF filters, with a proper installation, you should not need them. I've never used one in 30 years of install work.

That should clean up your noise. If it doesn't, then you need to start working through the rest of the system. I've had trouble cases like this and found running a separate ground wire from the radio chassis direct to body ground can solve some issues.
Get rid of the mag mounts and use permanent NMO mounts on the roof. Mag mounts do not provide DC grounding at the antenna base.

 

[AK9R]

I'm guessing it has to do with the Control Cable to Radio 1 that is causing a Ground Loop.

On the TK-x90 mobile radios, there's a ground wire in the control cable that terminates with a ring terminal. Next to the socket for the control cable is a screw that goes into a threaded hole in the steel chassis. That ground wire is supposed to be secured under that screw head. Not grounding that wire properly at both ends could cause some unpredictable problems.

 

[mmckenna]

Yep, good point.

Also, most modern vehicles use a sensor on the cable that runs between the battery negative terminal and the chassis/engine. Those sensors monitor power usage.
Connecting your negative power lead from the radios that is also grounded through the NMO mount, and maybe any mounting screws, gives an alternate return path to the battery that bypasses the sensor.
Not sure if the 2000 Expeditions have that or not, but newer vehicles will. Usually there's something in the owners manual telling customers not to connect the negative lead directly to the battery.

 

[AK9R]

Not sure if the 2000 Expeditions have that or not

I don't recall my 2002 Expedition having any kind of battery monitoring. My 2011 F-150 did have battery monitoring.

 

[Q12]

Thank you for the Replies

I have since Redone the ground for the control Cable as without it whine was still heard.

Next step I'll be looking at is Removing Antenna from the Radio and Opening the Squelch and Tunung into a NOAA Transmitter and see if any Whine is heard still.

If so then It is the NMO Antenna Reaching ground before the Negative Cable and I think using Chokes would solve that.

And also was thinking of using Chokes on the Control Cable Connecting Radio 1 and Radio 2.

I'll Try the Grounding Both radios to The Vehicle Body Route aswell, Would they need fuses on that Line to the Body Ground?

 

[mmckenna]

Would they need fuses on that Line to the Body Ground?

No. No fuses needed on the negative side.

 

[tweiss3]

Friend had this issue pop up on his accord all of a sudden. Everything was grounded, ended up being a pre-indicator to a failing voltage regulator in the alternator. Pulled the alternator, tested and it showed just below acceptable specifications. Replaced with new remanufactured and the whine is gone.

 

[Q12]

Friend had this issue pop up on his accord all of a sudden. Everything was grounded, ended up being a pre-indicator to a failing voltage regulator in the alternator. Pulled the alternator, tested and it showed just below acceptable specifications. Replaced with new remanufactured and the whine is gone.

I think this is the Route I will be going with

I grounded Both Radios to the Body instead of the Battery.

Put RF Chokes on the control Cable Leading from Radio 1 to Radio 2.

Still noise.

 

[TGuelker]

alternator

As a retired mechanic, the alternator seems to be a likely culprit. If you have a scope, check for AC voltage at the battery terminals with the engine running. Whatever you do, don’t EVER disconnect a battery cable with the engine running unless you have an older vehicle with a generator.

 

[thesoundman]

If you have a multimeter you can check for any voltage differences between +/+ or -/- from the terminals of one radio to the other. Ideally they should be matched. Have you tried connecting (-) from both radios together, or are they already grounded to the same spot on the body?

 

[mrweather]

The vehicle is over 20 years old. If it's still on the original alternator, it may be failing.

 

[AK9R]

Good point about the alternator. I had a 2002 Expedition and the alternator failed at around 80k miles.

 

[thesoundman]

Probably also worth making sure your battery isn’t dying, since it acts as a giant capacitor. If its charge is reduced its capacitance would be as well, potentially affecting its ability to filter normal alternator noise.

But of course that could either be the problem (battery itself is dying) or a symptom (alternator dying —> less able to keep battery charged), and as others have pointed out the alternator is definitely a suspect.

 

[Q12]

If you have a multimeter you can check for any voltage differences between +/+ or -/- from the terminals of one radio to the other. Ideally they should be matched. Have you tried connecting (-) from both radios together, or are they already grounded to the same spot on the body?

I've not Tried Grounding them Together or to the same spot on the body but will do so later today.

And by what you mean on checking for Voltage differences , Stick both probes in the two Power leads and see if there is any change?

 

[prcguy]

The fact that when the control head is ungrounded there is no alternator whine means the alternator is fine and not producing excessive noise. It also means there is a difference ground potential between the radio chassis and control head and the cable shield between the radio chassis and control head is trying to equalized the ground potential and some minor current is flowing on the shield of the control head cable. You need to provide equal ground potential to the radio chassis and control head so I would take the advice of running both power and ground cables from the radio chassis direct to the battery and try a ground cable from the battery to the control head ground. That will sometimes fix the problem. Or you may have to float the control head from ground.

If you try this advice try disconnecting the DC line filters as they can put resistance between the radio chassis and ground.

 

[Oa_Wrekt]

Do not run the grounds back to the battery. Ground the radios, control heads (if required) and power filters to the vehicle chassis within a few feet of the radio to a good location on the vehicle. Also check the vehicle grounds under the hood to make sure they are intact and sufficient.

 

[thesoundman]

I've not Tried Grounding them Together or to the same spot on the body but will do so later today.

And by what you mean on checking for Voltage differences , Stick both probes in the two Power leads and see if there is any change?

You want all equipment that’s operating together to see the exact same power (~+14.4V) and ground (0V) conditions. If that’s happening, you should see 0V when connecting your meter across radio1(+) -> radio2(+), as well as when connecting across radio1(-) -> radio2(-).

Coming from the car audio world I’m not super familiar with radio setups but the principles are similar. Does the control head have its own power connections or is it powered by the connection to the radio units? @prcguy ’s comments about equal potential are spot on.

Although I’d disagree on grounding directly to the battery. Just make sure you have a solid chassis ground, and all equipment is ideally grounded together.

 

[Q12]

[SOLVED]

After Emailing K0BG, Master of Mobile Installations.

Just treat the Radios as one.

By That, Ground both to the Body of the Vehicle at the same Point and Voila! No Alternator Whine!

It was such an Easy fix I couldn't believe my ears.

Thank you to all who chipped in to help!

Hopefully Someone in the future stumbles on this Information Finds the solution to their Issue here!

https://imgur.com/11ApY8a

 

[AK9R]

there is a difference ground potential between the radio chassis and control head and the cable shield between the radio chassis and control head is trying to equalized the ground potential and some minor current is flowing on the shield of the control head cable.

On the TK-x90, there's only one power connection even with a separate control head. The head gets its power from the RF deck. In the case of dual-deck single-head, I'm not sure which deck powers the head so that could be a potential issue if both decks don't have the same power supply and same ground.