Radio Noise

[Lonnie Wiggins]

My '69 L68 has all the ignition shielding in place, but there's still considerable noise on the radio.

The car is equiped with the TI ignition. Would the TI unit take a special condesor? I simply haven't been able to find any info in my reference material.

[Jack H.]

Re: Radio Noise

If you're talking about the capacitor used on the ignition coil to 'hush' broadband RF noise, I'm pretty sure it was NOT used on TI equipped cars. TI was accomplished by using a monster amplifier to 'blow up' a magnetic image of the pulse wave train associated with distributor's rotation and firing order, then stuff a current based replica of this waveform back into the coil. Hanging an RF reducing capacitor on the coil changed/interfered with the process.

On 'noise' you need to be a bit more specific and get prepared to do some sleuthing to track down the source(s). Is it 'popping/crackling' in lockstep to engine RPM/plug firing? Is is a 'whine' that varie with RPM. Is it constant/broadband 'hiss'? Is it AM or FM specific? All these symptoms point to the source(s) of the problem.

Noise in radio can be conducted (along power supply line and into the radio that way) or transmitted (airborne and into the radio by way of antenna). Fault isolation varies with source. The typical starting point for troubleshooting is with the antenna.

Unplug car's existing banana plug antenna lead-in from the rear of the radio chassis, substitute any fresh Wal-Mart/Radio Shack antenna and see if problem goes away. Note, Corvette antenna is INTENTIONALLY mounted on the rear of the car to get far back/away from engine compartment. So, when you install the temporary substitute antenna, it's handy to have a 'helper' walk it out the door, toward the back of the car, and move antenna through a positional arc as a cockpit observer monitors radio reception.

This simple $5 diagnostic should help fault isolate between conducted and radiated noise. If this solves the problem it's time to replace your worn out antenna lead-in cable and make sure the antenna's body mount ground plate and ground strap are installed properly. In rare cases, the antenna open circuit fault can lie in the antenna itself, but this is the exception rather than the rule.

If you determine the problem is NOT radiated, now you're into Pandora's Box because there are umpteen places where conducted noise can be at fault INCLUDING the radio's own internal power line noise trap components....

[Lonnie Wiggins]

Good Grief!

Now I know why about the only thing I know about electricity is how to put a plug in a wall socket.

Well, the noise is the static/poping type that is rpm dependent, on AM band only. FM is clean.

Thanks for the input - It'll give me a place to start.

Right - capcitor, not condensor. The reason I thought one belonged was because there was an old case of one attached by it's bracket to the coil bracket. So I figured it belonged there. I won't replace.

Thanks.