Home
New  Equipment
Used Equipment
Our Office
What We Do
Web Links
Tech Tips
Engineer's Log
Friends
Personal
Contact Us

Radio Broadcast Technical Consulting and Sales
 
10032 Island Drive, Brainerd, MN  56401

 


Technical Tips from Mark W. Persons
AM Radio Noise in GMC Savana Van


Summer 2009:  That's me, Mark Persons, squinting into the sun next to my 2009 GMC Savana service van.  With all wheel drive, it is an excellent vehicle for getting to and from transmitter sites in the middle of nowhere.  Sometimes on a farm.

Unfortunately the vehicle also comes with plenty of electrical noise that causes considerable interference to normal AM radio reception even with the factory installed radio.  The pop-pop-pop of impulse noise could be plainly heard even in the 1 mv/m signal contour of almost-local radio stations.  

A service tech at the local GMC dealership said he has thrown up his hands on trying to solve the same problem for other GMC car and truck owners.  He tried replacing the radio, the antenna, and more without success.    

A Potomac Instruments FIM-41 AM Field Intensity Meter confirmed that the electrical noise is definitely coming from the engine compartment and is related to engine speed although my take on it is that the noise is coming from the fuel injectors rather than the ignition system.

Since the engine compartment is difficult to get into I started by experimentally touching copper braided cable between body parts and the exhaust system under the van.  This showed immediate improvement so I mad it permanent.  Here you see the braid that is tin coated copper braid.  This coating helps slow down corrosion, which is inevitable especially on salt covered Minnesota roads in the winter time.     

 

Because the van has a Vortec V8 engine, there are two exhaust manifolds, which combine to a common exhaust pipe about half way back under the vehicle.  The photos show this braid going to the frame and some sheet steel as well as to the exhaust pipes.  I used steel wool to clean the area of the exhaust pipe to be connected to and then stainless steel external star lock washers to make sure a good electrical connection is made under the bolts and under the hose clamps.  I drilled and tap two holes in the frame, one for each exhaust manifold connection.  The hardware is 1/4-20 brass.  Most hardware is chrome plated.     
The result is about a 15 dB reduction in electrical impulse noise on the high end of the AM radio broadcast band and about 10 dB reduction on the low end of the band.  This is NOT the complete solution, but just a beginning of the quest to fix the problem that General Motors has apparently not addressed. 

Engine electrical noise can still be heard in the factory installed radio.  I know the noise is not conducted by the 12 VDC power line to the receiver because the noise goes away completely when the antenna is unscrewed from the fender mount.  

If YOU have any more information that might help solve the radio noise problem in GMC vehicles, I would like to hear from you about it.  Please e-mail me: teki@mwpersons.com 

 

September 19, 2009, a month or so from the first attempt, I am still looking at the problem under the hood.

 

 

This photo shows bonding the computer to the van body on the driver's side, under the hood.  Silver plated copper strap, the same as we use in AM broadcast work, worked well here.

 

More strap, this time on some kind of control module on the driver's side under the hood.  Bonding this and the previous module made a noticeable improvement in noise suppression.
As long as the hood was open, I bonded the hood to the vehicle frame using tin coated copper braid next to the radio receive antenna as shown here and on the driver's side as well.  This did not completely solve the problem, but it helped.  

If YOU have any more information that might help solve the radio noise problem in GMC vehicles, I would like to hear from you about it.  Please e-mail me: teki@mwpersons.com 

 


October 29, 2014:  Mark, I ran across your great website full of tips and tricks this week and have been spending time looking at them. Just wanted you to know that your tip on reducing AM noise on your GMC van worked on my 2006 Chevy HHR. Since I got this car two years ago Ive been having lots of ignition noise while listening to distant (100 mi) AM stations. Couldnt figure it out since the spark plug wires on this thing are something like 6 inches long! I read your tip to ground the hood and did that yesterday when I got home, also ran a braided wire from the body to the engine and NO MORE NOISE!  Ive enjoyed looking at your other tips on the page too, lots of great info there! Dave Land, Ponca City, Oklahoma.

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 
Mark W. Persons   Ham WMH
  

  Questions?  Email Mark Persons:  teki@mwpersons.com     

   Return to Home Page

page last edited 02/24/2016