RF noise gremlin
August 19th, 2020, 06:18 PM
#1
Registered User
Thread Starter
Join Date: Jul 2019
Location: Cincinnati, Ohio
Posts: 92
RF noise gremlin
Hi Guys,
What's the best way to track down where radio frequency noise may be coming from? I have a 72 Supreme (H/O) that has modifications. I have installed a Gear Vendors OD, HEI and an Atomic EFI system. My OD control box shuts itself off at times. The Gear Vendors tech squad told me that RF noise and/or voltage swings were what was causing my unit to shut down. The fix they say is to put a switch on the hot source and just turn it off and on to reboot it. I installed a SS voltage regulator and it seemed to help a lot but not the final answer. My voltage gauge rides between 12 and 14 now. But when I installed a radio the sound/signal is interrupted every 2 seconds or so with dead air. When the engine is turned off the stereo is perfectly fine. All suggestions welcome. I am thinking that I should first bench test the alternator? Then maybe isolate the distributor like GM did on Corvettes. Thanks in advance for your time
What's the best way to track down where radio frequency noise may be coming from? I have a 72 Supreme (H/O) that has modifications. I have installed a Gear Vendors OD, HEI and an Atomic EFI system. My OD control box shuts itself off at times. The Gear Vendors tech squad told me that RF noise and/or voltage swings were what was causing my unit to shut down. The fix they say is to put a switch on the hot source and just turn it off and on to reboot it. I installed a SS voltage regulator and it seemed to help a lot but not the final answer. My voltage gauge rides between 12 and 14 now. But when I installed a radio the sound/signal is interrupted every 2 seconds or so with dead air. When the engine is turned off the stereo is perfectly fine. All suggestions welcome. I am thinking that I should first bench test the alternator? Then maybe isolate the distributor like GM did on Corvettes. Thanks in advance for your time
August 20th, 2020, 04:18 AM
#2
Running On Empty
Join Date: Jul 2018
Location: Earth
Posts: 19,280
The issue is probably contained within the radio power supply wire. Since you installed a radio, I'm guessing you installed an aftermarket radio and it's not the stock OEM radio? Consider finding an alternate power source for the time being so as to hopefully rule out the source of the noise e.g. go directly to the battery, go directly to the fuse panel instead of your current power source. You didn't mention your current power source but you're most likely wiring through the ignition so the radio turns ON/OFF with the vehicle. It could be the EFI, HEI, SS VR and/or quite possibly electric choke wiring (if installed) depending on how you wired those systems. Many aftermarket radios come with a filter built into the power source lead wire which acts as an RF trap. You can purchase these from Radio Shack or other electronics stores. You might consider installing an RF trap (filter) into the power source lead wire. However you installed the radio try to ensure the power source lead wire is not running next to another known system if possible. Again, my first attempt to isolate the source would be to find an alternate power source to see if that in itself removes the noise and thereby isolates the issue to the radio power source lead wire then move on from there. Drop by an automotive electronics store who performs automotive sound system installations good chance they're familiar w/ your situation and might provide some helpful advice.
August 20th, 2020, 05:19 AM
#3
Moderator
Join Date: Jul 2007
Location: Edmond, OK
Posts: 16,273
How do you have your OD box wired?
August 20th, 2020, 06:30 AM
#4
Registered User
Join Date: Jan 2010
Location: central Indiana
Posts: 5,367
I had the same issue when I first installed my gear vender. After moving wires and trying a bunch of other things they suggested might help, they sent me one of the old school analog control boxes. It’s much smaller than the newer control module. Since then, it’s worked as expected.
You might consider removing the original alternator with external regulator and upgrade to a newer CS style. I’m guessing the new electronics would be much better shielded against noise.
What ignition system are you running? Is the ignition condenser in place? Do you have alternator or ignition noise on the radio?
You might consider removing the original alternator with external regulator and upgrade to a newer CS style. I’m guessing the new electronics would be much better shielded against noise.
What ignition system are you running? Is the ignition condenser in place? Do you have alternator or ignition noise on the radio?
August 22nd, 2020, 09:57 AM
#5
Registered User
Join Date: Sep 2010
Location: Norfolk, Va
Posts: 1,388
90% of engine and ignition noise issues are ground plane related. I installed stereos for 15 years and there are some very simple steps to isolate the cause.
First- make sure the battery to engine ground is clean and secure. No corrosion around the ends of the cable, no major grease around the bolt at the engine end.
Make sure the ground strap between the engine and the body/firewall is also clean and tight. This one causes a LOT of problems! If you have an amplifier with the stereo, you may need to increase the size or add another one.
The factory radio power lead is perfectly acceptable for powering a low-power aftermarket stereo. The factory lead is routed from the ignition switch to the fuse panel and then to the radio so unless the wiring has been horribly mutilated it will not introduce noise. If you have a high-power stereo, you will have one larger power wire that feeds the internal amp. This is usually the constant lead and should be connected to the battery or horn relay. Make sure you have a good solid ground wire to the metal dash structure! If you have an external amp, keep the ground wire nice and short. Scrape the paint away from the grounding point. Try isolating the amp chassis from the car body and do not run the RCA cables next to the battery power lead, run them down opposite sides of the vehicle.
Antenna! This one can be a big source of noise! Make sure the base of the antenna is tight. There are usually "teeth" on the bottom of the antenna to dig into the metal of the fender when it is tightened. Make sure the inside of the fender is clean and makes a good connection to the antenna. Make sure the coax from the base of the antenna is in good condition, no kinks, scrapes, or exposed shielding. Also, make sure the antenna coax does not go through the engine bay, it needs to be routed down through the factory hole locations through the kick panel area to the inside of the car.
Corvette's shield their ignition systems because they have fiberglass hoods. If you have a steel hood, there is no need to add more shielding. If you are running solid core plug wires you need to make sure EVERY component of the ignition system has a good solid, CLEAN ground.
Charging system noise can be a real beast to isolate, but again, there are some simple items to look for. Make sure you have a good capacitor/condenser on the regulator. Make sure the alternator case has a good ground, freshly painted brackets and engine blocks don't usually have a clean path to ground so make sure there is clean metal at all connection points between alternator case and engine block. Have your alternator tested to make sure it doesn't have a leaky diode. Make sure the charging lead from the alternator to horn relay is in good shape. Not frayed or spliced. I have seen some really corrupted charging leads! Make sure the charging lead is big enough to handle your charging system needs, if you have upgraded the stereo and other accessories so that they exceed the factory charging system you may need to get a higher amperage alternator and charging lead.
Adding a "noise suppressor" should only be considered after all of these things have been checked. They do work, but it is best to have everything else in good shape first.
First- make sure the battery to engine ground is clean and secure. No corrosion around the ends of the cable, no major grease around the bolt at the engine end.
Make sure the ground strap between the engine and the body/firewall is also clean and tight. This one causes a LOT of problems! If you have an amplifier with the stereo, you may need to increase the size or add another one.
The factory radio power lead is perfectly acceptable for powering a low-power aftermarket stereo. The factory lead is routed from the ignition switch to the fuse panel and then to the radio so unless the wiring has been horribly mutilated it will not introduce noise. If you have a high-power stereo, you will have one larger power wire that feeds the internal amp. This is usually the constant lead and should be connected to the battery or horn relay. Make sure you have a good solid ground wire to the metal dash structure! If you have an external amp, keep the ground wire nice and short. Scrape the paint away from the grounding point. Try isolating the amp chassis from the car body and do not run the RCA cables next to the battery power lead, run them down opposite sides of the vehicle.
Antenna! This one can be a big source of noise! Make sure the base of the antenna is tight. There are usually "teeth" on the bottom of the antenna to dig into the metal of the fender when it is tightened. Make sure the inside of the fender is clean and makes a good connection to the antenna. Make sure the coax from the base of the antenna is in good condition, no kinks, scrapes, or exposed shielding. Also, make sure the antenna coax does not go through the engine bay, it needs to be routed down through the factory hole locations through the kick panel area to the inside of the car.
Corvette's shield their ignition systems because they have fiberglass hoods. If you have a steel hood, there is no need to add more shielding. If you are running solid core plug wires you need to make sure EVERY component of the ignition system has a good solid, CLEAN ground.
Charging system noise can be a real beast to isolate, but again, there are some simple items to look for. Make sure you have a good capacitor/condenser on the regulator. Make sure the alternator case has a good ground, freshly painted brackets and engine blocks don't usually have a clean path to ground so make sure there is clean metal at all connection points between alternator case and engine block. Have your alternator tested to make sure it doesn't have a leaky diode. Make sure the charging lead from the alternator to horn relay is in good shape. Not frayed or spliced. I have seen some really corrupted charging leads! Make sure the charging lead is big enough to handle your charging system needs, if you have upgraded the stereo and other accessories so that they exceed the factory charging system you may need to get a higher amperage alternator and charging lead.
Adding a "noise suppressor" should only be considered after all of these things have been checked. They do work, but it is best to have everything else in good shape first.
Last edited by cjsdad; August 22nd, 2020 at 10:04 AM.
August 22nd, 2020, 01:04 PM
#6
Registered User
Thread Starter
Join Date: Jul 2019
Location: Cincinnati, Ohio
Posts: 92
The power line for the overdrive I wired directly to the ignition tab on the fusebox. I will go over all the different grounds and hopefully find the culprit as I did repaint everything including the engine block. I used the cars original dash harness and wanna kick myself for that tightwad decision. American Autowire made an engine harness for me that had the HEI conversion but I'm thinking somewhere something is not grounded very well. The car does have the metal framed fiberglass hood and the windshield antenna.
Thanks for all of these suggestions, very helpful everybody and the satisfaction of fixing stuff myself is well worth the effort to me.
Thanks for all of these suggestions, very helpful everybody and the satisfaction of fixing stuff myself is well worth the effort to me.
Last edited by EdwardB; August 22nd, 2020 at 01:27 PM.
August 22nd, 2020, 01:19 PM
#7
Running On Empty
Join Date: Jul 2018
Location: Earth
Posts: 19,280
The simplest test would be to run a hot wire directly to the (+) battery and run a ground wire directly to the (-) battery. You would not expect any noise. If you get noise, the positive lead to the horn relay or generator might be suspect, the ground wire to block could be suspect, or the antenna could be suspect (disconnect the antenna see if it makes a difference). Next, leave the ground hooked up to the battery ground, and run the hot wire lead to your ignition tab on the fuse box - see if there is noise. Run the test again w/ the hot wire directly connected to the (+) battery but change the location of the ground and see if you get noise. Through a process of elimination hopefully you'll resolve the issue; and as cj pointed out, ensure all your connections are clean and tight.
Thread
Thread Starter
Forum
Replies
Last Post
BSiegPaint
Electrical
26
May 30th, 2018 07:16 AM
