Squelch and Noise Problems with engine

[KD7DXI]

I own the Yaesu ft-1500 and the Larson window mount antenna single band.  My power leads both go directly to the battery and my coax cable runs along the side of the car under the carpet.  This is all installed on a 1990 Isuzu Trooper.  Anyways, When the car is not running the radio works great and the antenna works ok.  Then when I start the car everything goes bad.  Static is coming from somewhere and so when I scan I have to have the squelch at 14 and the RF squelch at at least 4 to even scan without it stopping on every channel.  My Friend has same radio and it has no problems what so ever.  Also when I am recieving on a single channel I can hear a slight fuzzy noise which changes when the RPM of my vehicle changes.  This is becoming very frustrating.  My antenna is also top of the line running at $70 and it doesn't work at well as my friends older antenna with a ground plane wire.  Does the ground plane wire really make a difference or what? What should I do?  

[KC8AXJ]

I bought a Power noise filter from Walmart that wires inline with your power leads to the Radio. They are made for Car stereo systems so you'll find them in that department. I had to have this for my handheld to get the noise out of it. Something you could try before that is to have your radio on, squelch off and remove the coax and see if the noise(s) disappear. If they do the noise is most likely coming in through the antenna system, not the power leads. Normally these radios made for mobile have filtering (12 volt)built in . As far as Antenna "performance" Larson is a very good choice. Your vehicle roof should be MORE that enough ground plane for your antenna if it is mounted high enough so it can "see" metal beneath(most of) it.
Did you check SWR ??
Good Luck
Steve kc8axj@arrl.net

[KL7IPV]

There are a number of things you can do. Radio Shack sells a filter that runs about $20 (last time I looked) and handles about 20 amps. It takes the AC component off the DC line and routes it to ground thru a capacitor. If you haven't fused or used a circuit breaker on each side of the DC lines do it NOW! It wont help the noise but will protect the radio. Be sure all wiring connections are TIGHT. The battery, the regulator, the altenator. Everything! You can also be sure you are using RESISTIVE spark plugs in the engine too. I also have run DC wiring thru grounded braid to lessen the noise. You should also take the vehicle to a battery shop and have them do an electrical check on the altenator to be sure no diodes are blown. It will run but make lots of noise if a diode is bad. Sometimes moving the antenna to another spot on the vehicle will cure a noise problem too. If all fails, it may be time to buy a BRAND NEW vehicle. Heck, any reason for that can be a good reason, huh? LOL
73
Frank
KL7IPV

[W3GEO]

Hello,

You have received some good advice on curing the noise problem and the only thing that I could add to it is that you make sure that you are using the right surpressor plugs and good quailty 8mm or thicker ignition wire.

The Larson antenna is a different situation. I have two of these which work ok on some vehicles, somewhat poorly on others and not at all on vehicles which have passivated glass installed. I do not know if the Trooper has that kind of glass but if it does, that is probably your problem area. Your dealer's parts department can tell you if it is. I had this problem some years back on a 91 Chevy Lumina Mini Van.
Correspondence with Larson brought the passivated glass problem to light. It has been my experience that any through the window VHF / UHF antenna does not work as well as an antenna mounted either to the vehicle body or a rooftop magnet mount.

73,
George
W3GEO