pictures

All modules connected

This pictures shows the spectrum from 1 to 100 MHz


I found out why the shown signal strengths are dependent on the center frequency.
The problem is that the sweep speed is too high. The faster the sweep the lower the amplitude. The sweep speed is not constant so the amplitude of the measured signals changes. For low sweep speeds the problem does not occur. I can use 2 MHz/div using a sweep frequency of 32Hz. So I have to decrease the sweep frequency. I will use 1 Hz. as sweep frequency.

testing new analog board

The new analog board works. Blanking caused some problems but I was able to solve them. Now I can see a spectrum. Pictures will be posted soon. Still a lot of work has to be done.

The analog board integrates the signals from the DAC. The DAC generates 2 ramp signal that consists of 10 steps. One is linear. It is integrated by the analog board. This signal goes to the x input of the scope. The other ramp signal is not linear. It is adapted to compensate the non linearity in the tuner. This signal is integrated. Then it is used to sweep the tuner.

I had a problem with the blanking of the tuner sweep signal. The integrator is a RC lowpass filter. During the blank the value of R must be very low. This way the voltage over the capacitor quickly drops to the input voltage of the filter. I use a j310 FET as a bypass switch over the resistor of the RC filter.

I have a few problems to solve:
-Sweep speed is too high for a span of 50 MHz per division. I may have to use a wider filter for this span. Tonight I'll try that.
-Measured signal changes when center frequency is changed. This is probably caused by changes in sweep speed.
-Alignment has to be done.