Transmitter causes siren to squeal

arlojanis · Post by **arlojanis** » Sat Nov 26, 2005 9:06 am

I have a CM300 radio and a Signal Vehicle Products Siren. The siren is a SS651 remote mount. When I key transmitter, the siren roars and squeals. Is there a modification or update for the siren?

wa2zdy · Post by **wa2zdy** » Sat Nov 26, 2005 1:43 pm

Make sure everything is properly connected, connectors are all well seated and such. Then make sure all the grounds are as they should be and are in fact connected to solid grounds.

After that I'd try some ferrite cores on each lead as it enters the siren and its control head. If that doesn't do it, your next step would be opening the siren up and installing bypass capacitors. But let's hope it doesn't come to that.

Let us know how you make out.

WB2IID · Post by **WB2IID** » Sat Nov 26, 2005 5:27 pm

You did not specify what band you're transmitting on, but I thought I'd tell of what I did.

One of our trucks (Dodge pick-up, around 2002 or so) was doing this same thing when the low band 110 W radio was fired up. I tried re-routing wires, grounding, ferrite beads (actually toroid cores with 2 or 3 turns) without success. The final solution was to take the siren unit apart and install .01 uF disc bypass capacitors on each of the connector pins. The problem was cured.

I don't remember what type of siren it is, I want to say Federal but I'm not sure. If I think of it I'll look tomorrow. I've never seen this problem in any other vehicles before or since.

The .01 uF discs are good at low band, if you are at high band I'd use .001 uF, and 470 pF for UHF.

Joe

arlojanis · Post by **arlojanis** » Sun Nov 27, 2005 10:56 am

VHF radio, 1/4 wave on top of cab, siren under driver seat, coax runs down passenger side, speaker in grill. Since siren has no off-on power switch it is powered all the time. Siren howl is worse at times and on some channels. Howl can happen when using siren or not.