70 MHz bandpass filter

When working on the 144 MHz bandpass filters, these were tunable over such a wide range that 70 MHz was almost in reach. Changing the  3pF capacitor for a 22 pF version did the job. The tuning was not optimum, it would have been better to use 10 pF caps and maybe a 6.5 turn inductor. Anyway with the 6 turn inductor it was a nice filter.

 

The plot for this filter. Vertical is 10dB per division, horizontal each division is 4 MHz.

In this configuration 50 MHz could not be tuned.

If you want to see the original article click HERE

Click HERE for a 50 MHz version.