21 September 2016

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.

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

18 September 2016

Revisit AD8307 Power Meter Calibration

This year at our club, annual pig picking BBQ and show-n-tell I had a chance to borrow the kind services of fellow Knightlites member OM John, KU4AF and his brand new and beautiful digital spectrum analyzer.

Connecting the Si570 based oscillator from my Sweeperino   into the Spectrum Analyzer and measuring the power level of the fundamental frequency we measured a -4dB difference in power when compared to measuring the squarewave on the AD8307 based wideband (~500MHz) Power Meter. Using a Low Pass Filter to filter out the odd numbered harmonics I resolved to measure the power in the fundamental on my work bench.

For the experiment I used the well known 10MHz calibration source as developed by K3NHI. This source can be used to establish the -10dBm point on the power meter through the measurement of a DC voltage level at the DC port. This reference is easy to build and is recommended for any homebrew starting out with a basic 50 Ohm bench.

Indeed my result showed a 4.1dB difference in power reading of the fundamental vs the wideband signal.

Herewith below are my Lab Notes of the procedure adopted.