The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Hello All:
I have a noise problem that I require help with. I’ve researched the problem but became more confused on what to do. I hope someone can help. Below I have listed the symptoms and my equipment.

Symptoms:
1) No noise with ignition off.
2) Noise with ignition on-engine not running.
3) Noise with engine running.
4) Noise does not change with engine speed, It is a constant sound.
5) No noise with coax disconnected from radio during #2 or 3.
6) Also I get sporadic noise with the engine running and standing still or driving down the road. It will read
up to ½ on the signal strength meter.
7) Noise does not change in with speed of the motor or truck. It is a constant sound.

Equipment:
Truck: 2006 Freightliner Century Class S/T has fiberglass body.
Radio: Connex 3300 hp.
Microphone: Road King 56B.
Coax: Belden RG-8X 14’-11/2”.
Mount: Firestik stainless steel mirror mount and stud.
Antenna: Wilson 2000 with 10” extension.
Power is connected to the battery terminal at the fuse box.
Ground is connected at the windshield post.
Ferrite core (snap on one’s) are used on coax & power cords.
Magnum power filter is also used..

I have all good grounds and continuity in the antenna system.

SWR is as follows:
CH1 1:5
CH19 1:3
CH40 1:2
Any advice would be greatly appreciated.

It seems like your car computer box is causing interferences in your radio. I experience the same with my VHF walkie when I connect the external ant.

Do you have a fuel pump relay on that Freight thing..?
If so pull it while you have the radio on and engine running..
Dose the noise go away while you have the relay in your hand.
The engine will run for a second or two while you do this .
this is the easyest way too test for fuel pump noise..
Gas or diesel it dosn't matter..

good idea, but you don't want to run a big truck out of fuel, they are a collossal pain in the ;;;; to re prime and get running. 2 filters to remove, fill, and replace. try a ground wire from the door itself to the frame of the cab. being your cab is on air bags, rear, and pivots, front, try grounding the whole cab to the frame. sand or grind a bare spot free of rust and paint and bolt on a ground wire or strap. don't forget there is a difference between electrical, mechanical, and radiated ground. there is no sutch thing as too much ground.

i believe, m & p audio sell a power cord with a noise reducer in-line. may or may not help, but might be worth the try.

As A truck Driver myself I can tell you there is no such thing as to much ground I had this problem with a Volvo 770 and had to drill a hole under my bunk and install a ground to the frame from experiance try and find any other electrical ground on the frame and ground to it or as close as possible. If this doesn't work try grounding your antenna also I had to do that also. Make sure to check your SWR's several times as they may drop or rise depending on the grounding...