New England QRP Club : The Excitement is Building....

I have two NEScaf filters mounted side by side in a small aluminum enclosure. The object of this project is (was) to give the CW operator the ability to split received audio into two signals either side of the CW offset. In theory the idea was sound but in practice I have two deamons I have to slay to make it practical. The same power source is used for both filters and a single audio input applies to both filter inputs.

1. Hum. I've tried several power sources at this point. This maybe due to the headset I am using being too sensitive. I am goiong to pass on this one for now.

2. 555 chip oscillations! This is a show stopper for sure. There seems to be only one sweet spot for the R9/R10 combo where filter self-oscillation stops. Moving away from that sweet spot generates varying oscillations heard almost as loud as the desired signal.

3. The separate filters oscillations are interacting. I can tune out the heard oscillations in either headphone with either combination of R9/R10. It is like the actual osciallation path is circular between the two boards themselves.

4. Repositioning (touching) the wires (parallel conductors molded together) to R9 effects the unwanted oscillations. These wire sets are approximatel 3" long to one filter and about 5" long to the other.

Decoupling of some sort is necessary I am sure. Other than removing one filter.... which defeats the project.... what might be done to break the path of oscillation? Other than the hum and the incredibly annoying self-oscillations the filters appear to work. Suggestions?

73,

Jerry, KG6TT

Fairfield, CA