Radio Interference

[medic834]

We have been experiencing radio interference while transmitting from a Kenwood VHF TK-790 mobile radio which is installed in a 2010 Freightliner M2 ambulance. This problem has been on-going for the past three months and we have nearly exhausted all options and resources in determining the source of this interference.

The ambulance is equipped with a Kenwood VHF TK-790 radio with dual heads. The first radio head is installed in the cab of the ambulance with the second installed in the patient care compartment of the ambulance. The RF deck is installed in the cab of the ambulance behind the drivers seat. The cable for the radio head in the patient care compartment ran through the wire chase with many other electronic cables and wires from the cab to the box. A "wind noise" can be heard in the radio transmission when transmitting and seems to become worse when the engine speed is increased.This wind noise at times causes the crews radio traffic to be very difficult to understand. We have swapped RF decks, microphones, radio heads, and cables with unsuccessful results in eliminating the wind noise. There is an in-line filter installed on the power cables for the RF deck and that has also been replaced. The alternator has been tested by our Freightliner service center and is reported to be okay.

One radio service center believes the interference is being caused by engine, while a second believes it is from other electronic devices or equipment in the ambulance. Any ideas or suggestions?

 

[ramal121]

Wow,OK. some questions. Does this happen on all transmissions, or certain conditions (like code-3)?
Does it happen from both front and rear? Are you using headsets or anything other than the Kenwood palm mic.

I am in the midst of a weird problem with a dual head 790 in a fire engine. I have a band-aid on the problem by disconnecting the rear control and awaiting customer approval to do more testing. Anyway, assuming the front control head is head one, try removing the cable from the radio chassis for head two and test drive the rig to see if the problem is still there. Then switch the cable on the chassis so the rear is plugged into the head one slot(and the front head is left disconnected). Have a grunt do some radio checks from the back as you drive around. See if any of this makes a difference. Report back and we could proceed from there.

 

[radionerd13669]

I have had this problem a few times.

Have you tried a Kenwood Line filter?

 

[ramal121]

I have had this problem a few times.

Have you tried a Kenwood Line filter?

The OP said he had one and has been replaced. To tell you the truth, I've had problems with them in the past and have removed them. Not for "wind noise", but other clams that have popped up.

 

[radionerd13669]

The OP said he had one and has been replaced. To tell you the truth, I've had problems with them in the past and have removed them. Not for "wind noise", but other clams that have popped up.

I am aware what he said! I asked if they have tried a Kenwood in line filter , he did not specify.
I have tried numerous filters on these but the Kenwood filters are the ones that worked. We never had wind noise. We had engine noise and a constant static when plugged into shore line ect.

 

[medic834]

Yes, there is a Kenwood line filter installed. This does occur from both the front and rear radio heads. Were going to ground the alternator and engine hood this week in hopes of eliminating the noise.

 

[medic834]

We grounded the alternator and engine hood with braided grounding strap and the "wind noise" still exists. What else is left to try?