[Milsurplus] Quick n dirty crystal selectivity - it no workee

[Hubert Miller]

"Series Resistance

Series resistance is the effective resistive component in series with the LC model of the crystal itself (see Figure 1). Oscillator circuits can tolerate some degree of series resistance, but not too much. A typical range is 25Ω to 100Ω for most crystals. The crystal vendor usually characterizes this resistance and specifies typical or maximum values for series resistance. Excessive crystal series resistance can lead to oscillator startup failure, so sufficient margin must be built into the oscillator design.

 

An exception to the above guideline is 32.768kHz wristwatch crystals, where series resistance can be in the tens of kilohms. Consequently, for this application the oscillator circuit must accommodate this high series resistance. Failure to address this will result in a 32.768kHz oscillator that does not oscillate. You should not expect to use an oscillator designed for a 10MHz crystal with a 32.768kHz crystal. It will not work."

 

Quoted from:  https://www.maximintegrated.com/en/app-notes/index.mvp/id/726            

 

I can see that since i don’t know the ESR of the crystal i put into the Command Sets receiver cathode, and it is shunted by something like a 300 ohm resistor, it looks like i will need an RFC in series

with the resistor to  have the crystal ‘work’ as a selective bypass. Otherwise the low resistance of the cathode resistor just negates the crystal. 

-Hue 

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