Chevy truck AM radio reception annoyance

[Elkins45]

I inherited my dad’s 98 Chevy K1500. It has a conventional fender mounted antenna. It also had a radio/cassette player. AM radio reception has been terrible for years plus I wanted something with Bluetooth, so I had Best Buy install a new modern digital receiver. AM reception was still terrible, so I replaced the antenna base. No improvement so I replaced the antenna mast. The only component I haven’t replaced is the section of coax between the fender and the radio. Replacing that most likely involves removing at least part of the dash and Who knows what else.

Anybody ever replace the radio antenna coax on a Chevy truck? How hard is it?

 

[Kansas_Ron]

There might be something in this article which will help.

Car audio noise suppression guide — diagnosing and treating noise problems in your car audio system

Diagnosing and treating noise problems in your car audio system

www.crutchfield.com

 

[Elkins45]

Th

There might be something in this article which will help.

Car audio noise suppression guide — diagnosing and treating noise problems in your car audio system

Diagnosing and treating noise problems in your car audio system

www.crutchfield.com

Thank you for that, but the problem isn’t noise. It‘s actually the opposite. The signal drops to nothingness momentarily then returns to normal without any observable cause or pattern.

 

[SubieRubyRoo]

I inherited my dad’s 98 Chevy K1500. It has a conventional fender mounted antenna. It also had a radio/cassette player. AM radio reception has been terrible for years plus I wanted something with Bluetooth, so I had Best Buy install a new modern digital receiver. AM reception was still terrible, so I replaced the antenna base. No improvement so I replaced the antenna mast. The only component I haven’t replaced is the section of coax between the fender and the radio. Replacing that most likely involves removing at least part of the dash and Who knows what else.

Anybody ever replace the radio antenna coax on a Chevy truck? How hard is it?

BEFORE you do that, pull the radio and check one thing… I know on Subies the antenna requires TWO wires hooked up to +12V, believe it’s the red and also the line that says “power antenna” (blue w/ white stripe) which one is oils think is for motorized… but antenna itself requires power. Linked it up with the red wire and ALL fuzziness went away. May want to check that out first

 

[Jimmy9190]

Intermittent or no AM is usually due to a bad antenna ground and/or bad coax cable. When the FM is not working is when you would likely have a bad tuner in the radio. The fix for this problem will most likely be to replace the entire antenna base, mast and coax cable. Given the age of the truck it would also be a good idea to either remove the fender liner for access or reach in through the access holes in the fender under the hood and clean the underside of the antenna mounting hole on the fender itself down to bare metal with a wire wheel or sandpaper so the new antenna will get a good ground. The antenna gets its ground from the metal base contacting the metal of the underside of the fender. Be sure to route the new coax cable away from other wire harnesses, electrical parts or power sources to avoid any radiated noise with the new antenna.

Best Buy may be able to replace the antenna, but it is pretty easy to DIY. Once you get the new base mounted to the fender just follow the old coax down to the grommet where it enters the cab. On a full size Chevy I seem to remember the grommet is kind of low on the passenger's side of the firewall below the HVAC box. From there it is super easy to route the coax to the radio. You don't even need any tools to do it. The dash panel just snaps off and the new radio should be mounted in a plastic installation kit that has a plastic snap on each side, just push those down and pull the radio/kit out of the dash and swap out the antenna connector.

Your new radio uses a larger standard Motorola style antenna plug. There will be an antenna cable adapter for the GM mini-antenna plug that Best Buy would have installed on your existing OEM coax, but you will not need that with a new antenna unless you are replacing the old antenna with a new OEM Chevy antenna with the smaller connector on the coax. Best Buy or Auto Zone or any good independent car audio store should have a good aftermarket replacement GM antenna on hand or they should be able to order one for you.

 

[Elkins45]

Intermittent or no AM is usually due to a bad antenna ground and/or bad coax cable. When the FM is not working is when you would likely have a bad tuner in the radio. The fix for this problem will most likely be to replace the entire antenna base, mast and coax cable. Given the age of the truck it would also be a good idea to either remove the fender liner for access or reach in through the access holes in the fender under the hood and clean the underside of the antenna mounting hole on the fender itself down to bare metal with a wire wheel or sandpaper so the new antenna will get a good ground. The antenna gets its ground from the metal base contacting the metal of the underside of the fender. Be sure to route the new coax cable away from other wire harnesses, electrical parts or power sources to avoid any radiated noise with the new antenna.

Best Buy may be able to replace the antenna, but it is pretty easy to DIY. Once you get the new base mounted to the fender just follow the old coax down to the grommet where it enters the cab. On a full size Chevy I seem to remember the grommet is kind of low on the passenger's side of the firewall below the HVAC box. From there it is super easy to route the coax to the radio. You don't even need any tools to do it. The dash panel just snaps off and the new radio should be mounted in a plastic installation kit that has a plastic snap on each side, just push those down and pull the radio/kit out of the dash and swap out the antenna connector.

Your new radio uses a larger standard Motorola style antenna plug. There will be an antenna cable adapter for the GM mini-antenna plug that Best Buy would have installed on your existing OEM coax, but you will not need that with a new antenna unless you are replacing the old antenna with a new OEM Chevy antenna with the smaller connector on the coax. Best Buy or Auto Zone or any good independent car audio store should have a good aftermarket replacement GM antenna on hand or they should be able to order one for you.

Since I already replaced the antenna base the only culprit remaining is the section of coax between the fender access hole and the radio. Thanks for the tip on the antenna ground: I didn’t scuff up the underside of the mounting point when I replaced the antenna base but that’s an easy enough thing to try.

Amazon has a magnetic base antenna for $10. I’m going to buy one of those and try it as a temporary to see if it fixes the problem before I try to replace that section of coax.

 

[PontiacHO]

Disconnect the antenna coax at the back of the radio. Securely tape mechanic’s wire to that end. Pull the old coax through the antenna mounting hole on the fender. Securely tape the new coax to the mechanic’s wire and pull the coax though to the inside of the cab. As was mentioned above there is a firewall grommet or plug. Find it and you’ll see how it is ran before beginning…

 

[JohnnyG]

Are there other radios in the house that get good AM reception in the same locations.
AM was always pretty terrible to begin with, and as a mostly neglected technology, I doubt that there's been any improvements.
AM signals are blocked rather easily by buildings and hills, Kentucky, unless in the city, wouldn't be the best location for good AM reception IMO.

 

[Elkins45]

Are there other radios in the house that get good AM reception in the same locations.
AM was always pretty terrible to begin with, and as a mostly neglected technology, I doubt that there's been any improvements.
AM signals are blocked rather easily by buildings and hills, Kentucky, unless in the city, wouldn't be the best location for good AM reception IMO.

The reception is much worse in this vehicle than any of our others when driven in the same locations. It’s a problem with this specific vehicle.

 

[MolaKule]

1) The radio should have an antenna tuning capacitor that is accessible from the outside. Check the radio's manual for this adjustment.

2) Most older radios require a coax with a 93 ohm impedance. Check the radio's manual for its required input and coax impedance.

 

[brianl703]

2) Most older radios require a coax with a 93 ohm impedance. Check the radio's manual for its required input and coax impedance.

93 ohm coax was known as RG-62. It's most common use, aside from car radios, was for IBM 3270 terminals and Arcnet (a LAN technology that was made extinct by Ethernet).

Newer (for the last probably 25 years or more) radios don't use trimmer capacitors for the AM radio section, they have an automatic tuning network that does the same thing automatically.

 

[MolaKule]

I inherited my dad’s 98 Chevy K1500. It has a conventional fender mounted antenna. It also had a radio/cassette player. AM radio reception has been terrible for years plus I wanted something with Bluetooth, so I had Best Buy install a new modern digital receiver. AM reception was still terrible, so I replaced the antenna base. No improvement so I replaced the antenna mast. The only component I haven’t replaced is the section of coax between the fender and the radio. Replacing that most likely involves removing at least part of the dash and Who knows what else.

Anybody ever replace the radio antenna coax on a Chevy truck? How hard is it?

What does the manual state wrt the coax and antenna impedance? What brand of radio and model?

Here's the problem, with the advent of Spiral, Fin, and Fractal antennas in automobiles the current coax impedance to the radio may not have the proper value, thus insuring a loss of signal level to the radio.

And even if the radio does have an internal antenna matching circuit, those circuits may only be able to span a narrow range of antenna and coax impedances.

Some of the newer antenna designs are actually six antennas in one housing:

Automotive Hexband Antenna for AM/FM/GPS/SDARS andAMPS/PCS1900 Cell Phone in an only 65 mm high Housing, IOP Conf. Series: Materials Science and Engineering 44 (2013).

 

[Elkins45]

This wouldn’t explain why it had the same problem with the original antenna and radio which were presumably matched from the factory. It also doesn’t explain why it is intermittently good with no identifiable pattern as to time or location.

 

[MolaKule]

This wouldn’t explain why it had the same problem with the original antenna and radio which were presumably matched from the factory. It also doesn’t explain why it is intermittently good with no identifiable pattern as to time or location.

Some possible reasons:

1) Rust at base of antenna not grounding properly to chassis, since chassis forms a ground plane for antenna,

2) coax center conductor (thin wire for 93 ohm coax) is broken somewhere, either between antenna and plug, at antenna, or at the plug itself.

 

[brianl703]

2) coax center conductor (thin wire for 93 ohm coax) is broken somewhere, either between antenna and plug, at antenna, or at the plug itself.

Should check it with an ohmmeter one probe on the antenna (alligator clip leads make this easier) and one probe on the center conductor of the Motorola plug. Move coax cable around while testing.

Broken coax would be expected to cause problems with FM too.

1) Rust at base of antenna not grounding properly to chassis, since chassis forms a ground plane for antenna,

My experience with car radios is that they'll get decent AM and FM reception even with a wire jammed into the antenna socket, no ground plane present.

 

[jhellwig]

On that series of truck I believe there is a connector in the antenna wire somewhere between the fender and firewall. Dad had an 89 salvage title truck that had bad radio reception till he had TV repairman fix the connector. Don’t know if the 98 still had it but if I recall it wasn’t that hard to get to although that was 25 years or more ago.

 

[Elkins45]

On that series of truck I believe there is a connector in the antenna wire somewhere between the fender and firewall. Dad had an 89 salvage title truck that had bad radio reception till he had TV repairman fix the connector. Don’t know if the 98 still had it but if I recall it wasn’t that hard to get to although that was 25 years or more ago.

Yes, there’s a short section from the antenna base that plugs into a connector inside the fender well. That co-ax section goes thru the firewall somewhere and goes to the radio. Since that’s the only original component remaining I think it’s the likely culprit. I’m just not looking forward to the bodily contortions and potential collateral damage involved in replacing it.

 

[meep]

Great suggestions already. Clean connections for ground and feed are super important. enjoyment of AM signals and programming is a rare thing, though with all of its disadvantages, there are still some technical advantages of AM, inckuding propagation and sunset transmission power rules remaining from a forgotten era, and unique cultural holdbacks that made radio special, still found in some places.