Spectrum Stalker

Posted on Feb 7, 2014

For one thing the Krohn-Hite 5100A VCO takes Zero to -17 VDC to drive the VCO output frequency. But the O-Scope X-axis wants 0 to +5. 7 volts to have the X-axis represent increasing frequency to the right. So, the O-Scope frame had to float to get -Volts into the KH 5100A and use same signal to get +Volts into the O-scope. Too confusing for a quick

Spectrum Stalker
Click here to download the full size of the above Circuit.

ie hookup. To facilitate easier setup, the above Spectrum Stalker box is under construction. This box will create 0 to +5. 7 VDC triangle and saw tooth voltage waveforms to drive the O-Scope X-axis. Internal Op-amps provide offset and gain to make the O-Scope X-axis Grid calibrated in frequency. In addition, the sweep range can be bracketed via HI & LO-LIMIT front panel knobs to display any portion of the frequency range. The KH Model 5100A Generator VCO has a response that may be in the 10`s of Hertz range so too high a VCO slew rate will cause the resonance bloom to shift from the correct frequency (x-position) on the O-Scope CRT. The Spectrum Stalker internal oscillator will sweep the O-Scope x-axis from a couple Hz to about 30 Hz. In the triangle mode, the resonance bloom will be seen with advancing and declining VCO drive volts. If the VCO output frequency is not tracking fast enough, the spectrum `bloom` will be seen to shift left and right. The higher the scan rate, the more the shift. The HI-LIMIT and LO_LIMIT knobs will permit bracketing the `resonance bloom` to increase repetitive scan rate while using slower VCO slew rate. This trick can minimize phase shift of the apparent resonance position for increasing versus decreasing VCO frequency. Saw-tooth waveform will also cause shift of the apparent spectrum, but just in one direction which makes a better picture. May have to do a O-Scope Z-axis blanking during...

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