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Measuring filter shape factor
http://www.lazygranch.com/images/radio/cwfilter.gif
I did this test as follows: 1) radio in AM 2) AGC turned off 3) RF generator connector to antenna input 4) distortion analyzer connected to earphone output Pick a frequency. I used 10Mhz. Set the RF generator and radio to that frequency. Leave the radio dial alone. Sweep the RF generator manually and measure the audio level from the distortion analyser. Plot the results. This was a crystal filter, so you will need a RF generator with 1Hz steps. This is an in-situ measurement, i.e. this is not the same as just testing the IF filter by itself. You need the distortion analyzer to get the audio signal level independent from the noise. All that said, Bush should be impeached. Michael Thorpe wrote: Amongst all these political propaganda posts, I wonder if there is a little room for a technical question related to radio please? If so, here goes: How does one measure the IF filter shape factor in a shortwave radio? I am technically minded and do have a signal generator, etc., but I am not sure of the exact procedure. Do I get the audio level at the peak frequency, then detune both sides off the peak for -3dB of the demodulated audio, note down the width between these points, then detune to obtain for -50dB of the demodulated audio, get the width at these points, and then the ratio of the two widths is the filter shape factor? I would appreciate a link to the exact procedure if there is one (don't seem to be able to find this in Google) or an expert advice please. I would also appreciate advice as to what actual values of filter shape are considered poor, good, excellent, etc... Thanks in advance, Michael |
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