Electronics 27

The notches are actually a design error on my part that I still need to fix. I know what is causing it and how to fix it just haven't done it yet. The problem was created because I was trying to cut corners bypassing the BCB Filter when it was switched out.

Here's the BCB Filter and how I wired it to either switch it out or in. I wanted to only use one relay which I had on hand. There were several reasons for this, 1) relay I had was SPST, 2) I didn't want to use two relays as this meant more current draw from the power supply which was already at 1.2 amps and 3) this seemed like a ridiculously simple solution. Can you already see the flaw in the design.

Here's the problem. When the filter is switched out there is actually still reactive components left hanging on the input line. Above is the equivalent circuit when the BCB Filter is switched out. These reactive components still hanging on the line is what's causing the notches at 1.4 MHz and 19MHz. And it also explains why the notches go away when the filter is switched in.

Here's the solution. The filter needs to be completely bypassed on both sides, duh! And I thought I was being clever. This fix will require me to etch a new ckt brd. I will eventually get around to it but for now I am living with the notches, at least I'm aware they are there and I do know how to fix it. For now, I'm moving onto troubleshooting an R-1051 synthesizer problem. Yes, finally, back on the bench.


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