I am really a newbie here in Electronics and I'm into it as a hobby/passtime. I was going through this simple coil-less Shortwave Transmitter circuit on a blog.

enter image description here Q1 – BC548, X1 – 10.7 MHz ceramic resonator, 3 terminal, C1 – 10 nF, C2 – 100 nF, C3 – 100 pF, R1 – 10 kOhm, R2 – 150 kOhm, R3 – 1 kOhm

My questions are:

  1. Does circuits like this work? I want to know how this circuit oscillates at a shortwave frequency without LC Tanks. Is it entirely done by the ceramic resonator?
  2. Can I create a similar circuit to receive Shortwave audio signal, which won't use a old-days coil and ferrite rod? If someone could help me with a simple circuit diagram for a shortwave radio receiver which uses such ceramic resonator I will be grateful. I couldn't find it on the web.
  • \$\begingroup\$ Your circuit does have a tuning element which is a ceramic resonator which tunes at 10.7 MHz approx .It is possible to make a simple fixed freq SW receiver .Your circuit will also transmit . \$\endgroup\$ – Autistic Feb 4 '18 at 0:07
  • \$\begingroup\$ It's a bit unclear what exactly you are talking about. Ferrite rod antennas are used for longwave like broadcast AM or at most medium wave, not for shortwave bands. But do inductors in general, or for that matter transformers constitute "coils" in your meaning? It is probably possible to build a software defined receiver with neither, but the point of this restriction seems to be lacking (and would you have to use a piezo earphone, rather than one with a voice coil working in opposition to a magnet?) \$\endgroup\$ – Chris Stratton Feb 4 '18 at 0:40
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    \$\begingroup\$ A major problem here is finding a ceramic resonator whose frequency matches the short-wave frequency that interests you. Although a ceramic resonator can be "pulled" in frequency over a short span, it cannot be pulled far. A LC resonator can be varied in frequency over a wide range. \$\endgroup\$ – glen_geek Feb 4 '18 at 3:41
  • \$\begingroup\$ A 10.7 MHZ resonator is nowhere near as accurate as a crystal. Your drift could be +/- 10% \$\endgroup\$ – Sparky256 Feb 7 '18 at 20:27

Ceramic and Crystal resonators are very high Q resonators with equivalent circuits the same as an LC parallel tank cct here. ( Q= 5k to 10k ) They work by passing a bandpass where the phase shift is 180 deg together with C3 such that with the inverting transistor the result is some gain with positive feedback to become an oscillator.

Which won't use a old-days coil and ferrite rod?

You would need multiple stages of ceramic and crystal bandpass filters. Coils are good for the intial stage LC resonant band filter with high passive gain.

Coils are very useful and should not be ignored. enter image description here But here are some ways of finding more info by adding keywords

  1. Yes, a circuit such as you've shown can emit rf. It functions similar to a pierce crystal oscillator...something for you to Google. However, without "old days coils " to form a tank circuit, there's a good chance it emits not only at 10.7 MHz but on 21.4 and 32.1 MHz as well. I won't go into licensing aspects here.

  2. A receiver can be as simple as a diode, capacitor, and a good ground and antenna. No coil. Of course, it will receive only the strongest signal and no way to tune it. On the other end of the no old days coil design, a fast A/D, a processor such as a DSP, sprinkled with software, you can have what's called a software defined radio or SDR.

Coils have their place. They're not something that goes out of style.


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