Analog Radio tech: test with a Local Oscillator the "book type" tuning capacitor of the 1920s (5MC)

Описание: Please read the description first, for the best and most complete information.

Final video 2 oct. 2025 (book capacitor project closed) is here
   • Book Capacitor Superheterodyne radio (pure...  

NEXT video (17 sep 2025, proper sine wave of a L.O. in the 7 MC band) is here
   • VLOG & Schematic & demo of a local oscilla...  

With a difference of 100 KC with the Local Oscillator on Shortwave (receiving radio stations between 2 MC-10 MC- or even higher, 10 MC-30 MC) it means that ideally 10 radio stations (each with a bandwidth of say 8 KC) fit into that (a certain) frequency band of 100 KC wide somewhere in the frequency spectrum on SW. Needs testing!

This is only a VLOG, though I show the schematic of the LO ( = Local Oscillator for a Superhet radio). Can also be used for many other purposes: testing radio coils, etc.

The Local Oscillator (LO) in a Superheterodyne radio generates a radio frequency that is somewhere between 450 KC and 460 KC apart (that is to say: difference!) from the radio signal received on the antenna coil.

The "book type" tuning capacitor where I am working on now for Shortwave is in this video
   • The "Book type" Radio tuning capacitor of ...  

Via the so called “mixer” (= frequency transformation, nothing is mixed up) we derive an IF frequency in the order of (say) 455KC, with a bandwidth of (say) 10 KC (or 8 KC or 4 KC or 3 KC or even smaller), through which we “look” to all the frequencies received on the antenna coil.

Say we "peep through" a hole of 10 KC (or 4 or 8 KC) wide to all the frequencies where radio stations work in the frequency bands, somewhere between 2 MC and 30 MC.

Especially on Shortwave this works very nice (2MC-30MC). It gives an enormous (!) selectivity.

For proper functioning, that LO must be good stable, otherwise the radio station received on the antenna “fades away” and not because of the (say) propagation on SW on frequency “X” in our earth atmosphere, but because of the instability of the LO.

But, because for the normal radio stations on SW (broadcast types) there is a bandwidth of say 8 KC, so it could be not too critical, that LO frequency, to receive radio stations on SW properly.

This is, by the way, only a first test about how the “book” capacitor from the 1920’s can work in this case, or helps us to tune the LO (Local Oscillator).

It is only a VLOG, though I also show the schematic of a properly working radio oscillator (Local Oscillator for a Superhet) for MW or SW, made with a FET. The BF 256 a or BF 256 b. Schematic is showed in the video.

Please note this is very important: that “book” capacitor with its capacitance in the order of 50 pF - 110 pF, is paralleled to the capacitor inside that (canned) coil, with its red core.

More info is in earlier video’s on my YT Channel. When I have time I will give relevant links, perhaps tomorrow or in the coming days.

My You Tube channel trailer is here:    • Radiofun232 on YouTube, find working & tes...  

Interested in certain electronic circuits? (Radio’s, audio amplifiers, audio pre-amps, audio filters, measuring devices to test transistors and (say) mosfets or (radio) coils or Shortwave and MW radio’s?

Go to my Channel Trailer (“Radiofun232 on YouTube”).

Via that (the "looking glass" = search) you can find specific video’s (under the say 1600 published). In almost all video’s a schematic is showed, if so: it is a working and well tested electronic circuit.

Keywords: ”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. Or https://www.lulu.com/search?adult_aud...

I keep all my YT videos constant actual. Search on YT and avoid my circuits that are republished, re-arranged, re-edited on other websites, giving not probable re-wiring, etc.

I take distance from all kinds of fake claims, made via people that are republishing my circuits via the www.

Upload 16 september 2025.

NB: Another relevant video is here.

   • TRF Radio for MW/SW. Can it work with all ...  

I show there "canned" coils, testing them on their oscillation properties. These coils can be used to generate frequencies with the help of this FET circuit (now & here, 16 sep 2025).

Test, try, experiment. The capacitors (I mean their values, of course) between Gate and Source and Source and ground of the FET form a capacitive voltage divider. That is extremely important (these 2 cap. values) in combination with the coil value (in Micro Henry, say 470 uH is a good start) in the source lead of the FET.

Do some experiments with these capacitor values (related to the frequency where the LO works) and/or a properly winded coil for MW or SW, to get the best sine wave on HF out of it. Say between 100 and 10 or 20 turns.
Upload 16 sep. 2025