HHS2200 - vehicle FM radio interference

[militarymedic23]

Would anybody be able to comment on possible causes for FM radio interference when the siren unit is on (not activated for tones, just powered on)?


I'm guessing with the more recent models of Whelen's siren units, the Cantrol, Cencom, newer 295 and the HHS are probably all designed/created around a similar circuitry, so the question would probably apply to any of these products.


I never noticed the FM interference when using an older 295HFS unit and separate lighting switchbox, but today I was able to determine that the 2200 unit just being powered on was generated very random sessions of FM radio interference. Turning off the unit made the radio audio crystal clear, turn it back on and there is a noticeable


difference.


The current installation has power for the unit coming right off the battery, through a fuses distribution box and grounded on the same metal frame point as the battery.


The interference seems somewhat minor at times, but randomly will generate enough interference it's like trying to listen to a station at the very fringe of the broadcast area, a lot of static.


If anybody can spell out suggestions/words of wisdom on techniques that may help address this...


Thank you

 

[Solvarex]

Bad ground would be the first place I'd start looking. My HHS has never interfered with my FM radio. Maybe try grounding closer to the unit.

 

[OutofCantrol]

Check your ground. Make sure you have a solid body ground. Try for a clean factory grounding point.

 

[militarymedic23]

I have some wiring supplies arriving in a few days and I'll tear everything apart then.


Currently I do have the ground wire running to the same bolt used for the vehicle's main grounding wire. I'm not on the electrical engineering side, but considering the vehicle body is the common ground, when trying to isolate noise by using a different grounding point, it is still a common/connected 'ground.' Or is the principle that the ground connection is being dispersed throughout the entire frame and therefore another ground point will experience only a fraction if any effect from the primary ground?

 

[wilsonbr90]

I would note more of the vehicle itself. Most of these new cars have internal FM antennas with poor coax. A break in the shielding on the coax or a headliner antenna might pick up the unwanted RF. Just my .02

 

[militarymedic23]

very true, but considering all this never happened until the 2200 was installed, there must be something in the wiring or unit. Looks like all my supplies will be here by the end of the week. then we'll see!

 

[bobbyj]

what else is on your fuse block?

 

[militarymedic23]

Actually nothing else right now. I favored the box since it took care of all the fuses instead of having a bunch of in-wire fuses.


I do have two ULF44 flashers that are powered through the 2200 unit and grounded to the same point as everything else. Those are only powered/activated through the 2200 and are not on when I'm hearing the static. Thought they were at first since when on I can here the flash pattern equivalent through the radio.