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Please read the description first. A video where I show how to test ceramic (“crystal”) filters in the 455 KC range, used as IF filters with a bandwidth of (often) 10 KC (KHz) or 8 KC.
It is only a VLOG, but everything is told & showed in the video.
There are, by the way, many SW & MW radio circuits on my YT Channel. These are analog circuits for MW and SW. Thus: TRF, Superheterodyne and more, say a more simple heterodyne.
You can see, via everything showed in this video, if such a filter “works” and on what frequency and whether the ceramic (or coil filter) is ”active” (thus usable for a IF amplifier on, say, 455 KC) or “dead” (=not usable).
When the ceramic or coil filter does not want to oscillate in the FET test oscillator and (thus) does not show its resonance frequency (somewhere between 450 KC and 460 KC) it is dead and not usable.
The schematic & demo of this test oscillator is here:
• FET test oscillator si...
When you bridge the input of this test oscillator with a tuning capacitor in the order of 20-300 pF the circuit gets more versatile (=better tunable for test coils or test ceramic filters).
Though, of course, that extra capacitance will bring the frequency of the coil or ceramic filter that you are testing down or up (…! ). In general down, btw.
Apart from the stray capacitance in the FET test oscillator circuit and the cables. That is all classical radio theory: idea of parallel tuning, adding extra (or smaller) parallel capacitance to a tuned coil or ceramic filter.
The effect is, in general, in this circuit, not so big.
More important and the crux of the circuit is this: get the coil filter or the ceramic filter into resonance to see if it is healthy and usable.
In a definite circuit, where you want to put the crystal or coil filter on say 455 KC in, there is always input and output parallel capacitance, from all kinds.
Just like here in this test circuit. Thus, in practice, such an IF amplifier setup must/can be tested with a sine wave generator (the one showed here), with which you can tune the complete IF amplifier to its frequency, with that 10 KC or 8 KC bandwidth.
So this test gives a very reliable idea about the usability of IF ceramic filter X or Y or IF coil filter X or Y, when put into a definite IF amplifier in the 455 KC range, with its 8 or 10 KC wide (say) audio band, it is the “window” through which we look at the different (radio) signals that we receive on our antenna.
NB: the idea here is/was to receive AM modulated radio stations, though any IF amplifier can also be made to receive FM radio signals, with another type of detector, say the ratio detector. More about that on the www.
My You Tube channel trailer is here: • Radiofun232 on KZbin...
Type there the keywords that you like (e.g. radio/audio/amplifiers/test/filter/) in the “looking glass” = search function” and give “enter”. Via that you can find specific video’s (under the say 1500 published).
When you search, search always “NEWEST FIRST” to get the right overview.
You can also search via the “looking glass” on my Channel trailer via keywords like ”audio”, “radio”, “amplifier”, “filter”, “Shortwave”, “transistor”, “FET”, “oscillator”, “generator”, “switch”, “schmitt trigger” etc; so the electronic subject you are interested in.
My books about electronics & analog radio technology are available via the website of "LULU”, search for author “Ko Tilman” there. www.lulu.com/search?adult_aud...
I keep all my YT videos constant actual, so the original video’s with the most recent information are always on KZbin. Search there, and avoid my circuits that are republished, re-arranged, re-edited on other websites, giving not probable re-wiring, etc. Some persons try to find gold via my circuits. I take distance from all these fake claims. Upload 18 May 2024.
More info here (wobbulator for 455 KC) • how to make a 455 KHz ...