I've got a prototype thingo on the bench, a small part of which involves heterodyning two basically identical oscillators, one fixed frequency, the other slightly variable +/- some hertz. I'm using an LM556, the dual version of the 555. The idea of having both oscillators on the same chip is that they track nicely for temperature. However whenever the frequency of the variable oscillator gets within cooee of the fixed frequency one, the bloody things injection lock together, and that screws up the function of my system.
It's built on breadboard and I do know that that is not the best, but I've routed all of the grounds properly and have bypassed the thing to death - the DC potentials at VCC and the unused VCO inputs are clean and there is no ground bouncing/spikes of significance at my timing caps with respect to the GND pin.
Does anyone have comprehensive experience with this chip? Is this a special feature of the 556? I wonder if the independent oscillators in such close proximity on the same silicon chip pickup each others totem-pole output driver switching spike. Should I attempt a PCB board or would I be wasting my time?