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RFI

Wonder if anyone else has come across this. I just finished assy of my new NEScaf and all works gangbusters with my regen. Only problem is I'm getting RF into the receiver from what I can only think is harmonics from the clock. Other than putting it in a metal case, does anyone have other ideas to solve this ? I'm using a 9V battery as B+ so it's definitely not mains borne. Thanks, Paul zs2oe

Comments

Paul-

Mounting the NEScaf in a shielded enclosure may help, if the signal is being radiated into your receiver.

Are you sure it is from the NEScaf? If so, then varying the clock frequency (adjusting  the center frequency pot) should cause a shift in the received signal. The clock runs at 100x the center frequency desired: i.e. 60 KHz for 600 Hz filter center frequency.

Are you using a separate battery for the NEScaf? Or does the same battery power the regen? Another possible path for coupling is through the B+ line, if it is common to both devices. Additional decoupling of the power supply lines can help. Also, low-pass filtering of the audio output of the NEscaf can reduce any clock "bleed-through".

GL, Bruce N1RX

Thanks Bruce. Yes, it's definitely the NEScaf, received freq varies with clock freq adjustment. The battery is independent too. Any thoughts on RF decoupling at the clock itself ? Though naturally I wouldn't want to be eliminating the fundamental !  I'll try the LPF approach on the audio - perhaps at the input too, seeing as that is the part of the circuit coupled to the receiver. Regards, Paul zs2oe