Triple Tuned Band Pass Filter Measurements

As a learning exercise I measured the characteristics of a Triple Tuned Circuit Bandpass Filter in my junkbox. This is a board that came from the now retired kit from the company Kits and Parts.com. This kit is called the multiPig+. Details of this kit can be found in the retired kits section of the aforementioned website. The measurement details are in my notes below. The 40M filter seems to be within spec and was relatively easy to align. Minimum IL = -5.8dB. However the 20M filter was difficult to align as can be seen from the Sweeperino measurements. Try as I might I could not eliminate the 'second hump'. I assume this is one reason why the IL = -9dB.

The experiment also illustrates the utility of the Sweeperino to understand exactly what the filter shape characteristics are in a fast efficient way.

http://hfsignals.blogspot.com/p/sweeperino.html

Next I will try to calculate the theoretical IL and BW for a triple tuned circuit and compare the results.

Characterization of a 14.5MHz low pass filter

 I built a Chebyshev n=5 filter and then tried to characterize it. Since I am using an 11MHz sine wave generator for calibration I started out with the aim of realizing a 13.2MHz filter. Refer to EMRFD Chapter 3 for filter design. Since I didn't have any 330pf caps on hand I ended up with a 14.5MHz (peak cutoff) filter using 300pF capacitors.

I was unable to detect the ripple in the filter. Instead it showed a flat response until about 9MHz with an insertion loss and ripple that I could not measure with my power meter.

The following results were obtained.

RL = 22dB
-3dB cutoff point = 15.61MHz
-5dB Passband = 16.4MHz.