28 June 2013

A Scope test of an NE602 Osc in my DC Receiver

I had to do some basic tests using my newly acquired antique test instruments! The pics below show the scope trace and frequency meter readings when looking directly at the oscillator pin6 of the NE602 on my DC receiver. As you can see, the trace shows a nice sine wave with no 'visible' distortion. How cool is that! I am now motivated to take many more measurements of the NE602 in my DC Receiver configuration.

You will also notice that the frequency of oscillation is 6961KHz. With no probe attached the resonant frequency is 7020KHz. Meaning that the effect of the 10X probe and scope input impedance is to add capacitance that will pull the frequency down by 59KHz. This is approximately an addition of 5pf in my oscillator configuration. Assuming the capacitance is 269pf at 7020KHz then this represents a 1.9%error. Acceptable?

The following results were recorded:

Test configuration. Scope connected to the NE602 Pin 6 (collector) on Channel 1 using a 10X probe and set at 20mV/Div. The frequency meter is connected to channel 1 of the scope via a BNC connector on the rear panel.

1) Voltage reading is 900mV (p-p)
2) Frequency reading is 6961.2Khz.

Observation: The spec calls for at least 200mV (p-p) on Pin 6. What would happen if I reduced the size of the feedback capacitors on the Colpitts configuration? In theory this should reduce the phase noise on the oscillator. The problem is that by doing that I would have to redesign the rest of the capacitive components in the circuit. No trivial task and only worth it if it would result in more oscillator stability and less noise.

Next I will use the sweep B function to see if I can see any phase noise on the oscillator signal.

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