Very sharp audio bandwidth filter with a 741 Opamp, demo & schematic and more ideas to develop it
The video & demo tell everything that is necessary. Music: copyright free by the 127 ers, e.g. "in Albany New York". Very good music to do audio tests, by the way. Correction to the video: I did not use the bandwidth filter in the past to detect FAX signals but RTTY signals (FSK-mode), so to discriminate "mark" and "space" (two different audio frequencies) in such a Shortwave transmission.
An experimental circuit to make a very sharp bandwidth audio filter. I don’t know whether there are nowadays (2019) RTTY (mark and space )signals on Shortwave transmissions, perhaps Radio amateurs use them still.
By the way: nowadays all Shortwave modes (say Morse, Fax, SSB, LSB, RTTY, FSK, etc.) can often in an easy way be detected/discriminated by Software/Software defined Radio: cheap & easy, you don’t need a 1000’s dollar analog radio any longer.
Anyway, the sharp audio band filter in this video is usable for all kinds of electronic applications, say in audio applications and more, say in driver circuits that drive (power) transistors on 1 specific frequency over a line that carries more audio frequencies, etc.
The audio effect that you hear in this demo is (as far as I know) sometimes described as “phasing effect”.
Take your time and (say) replace the two 10 N capacitors by 100 N (0,1 uF) capacitors or 4N7 (4700 pF) to get an overview about what this circuit can do for you in electronic practice in the audio band, say 20 Hertz up to 20 KHz.
I only tested it with these components and 10 N capacitors, so there is no “guarantee” that it will work properly on higher or lower frequencies (bandwidths), used with higher or lower values capacitors. Anyway: with a few experiments you can get the circuit easily under control for other audio bandwidths. Oscillations can easily be damped by varying somewhat with the resistors.
All the videos hat I have published on You Tube can be found via my Channel Trailer: Link is
• Radiofun232 on YouTube, find working & tes...
In thematic order you can find these video’s under the “comments” section.
Important: to find all the links to the (+/-700) video’s on my YT Channel, select, in the comments section, “NEWEST FIRST”
My books about electronics are available via the website from “Lulu”, search for author “Ko Tilman” there.
https://www.lulu.com/shop/search.ep?k...
There is an important video via which you can buy a document where I give links to many of my video’s, published between 2010 and 2018.
Link is: • Radiofun232: Links to my You Tube videos 2...
My books are also available via Barnes and Noble and via Amazon.
Regarding all my video’s: I constantly keep them actual, so the original video’s with the most recent information are always on YouTube. That is the source, and search there. When my video’s are reproduced or re-edited on other websites/channels you can not (!) be sure about the original content (=really working electronics) and important adaptations to the circuits.
Be aware of that, I saw on the internet many of my circuits reproduced in a poor or even not proper way. I can not help that, sorry. Upload 10 April 2019.