I'm working on project for school, and rather than simply buying a transceiver I want to build one. I'm studying Mechanical Engineering, so i virtually know scraps of signal transmission. All the schematics I have found want to convert an audio signal, from a mic, into a radio frequency. I just want to send a radio signal as a ping to another transceiver.

I'm hoping by removing the need for frequency conversion, the device will be smaller and require less power.

Less filtering and less amplification modules.


The idea is, if this represents a the block diagram of a transceiver, and I can remove the conversion requirements I can do away with the variable frequency oscillator, beat frequency oscillator, and mixers.

 

If you want to get to bare minimum, an oscillator is a transmitter, and a resonant LC circuit is a receiver.

 

If you want to get to bare minimum, an oscillator is a transmitter, and a resonant LC circuit is a receiver.

Yes, and it will have minimal range, and be interfered with by all nearby transmitters.

The simplest receiver is a super-regenerative circuit as used in the 315MHz and 433MHz remote control receivers all over EBay...

 

AM pulse code transmitter.

TRF receiver.Regenerative detectors are more sensitive but at a cost.
Note: Some would call the detector circuit a Reflex detector. It is not because the 22 uf capacitor filters out the baseband signal.

 

Radio Engineering is a very specialized field and signal transmission is just a part of it. That means you need years of studying and experience to design and build your own radios. The best choice for someone who doesn't possess this kind of expertise is to just stick with a reliable schematic used by others. DickCappels schematics seem legit and, even though I haven't tested them myself, I'll try to explain their function in broad terms.

In the transmitter, the attiny microcontroller creates pulses of 4MHz that feed a npn transistor which amplifies them. In that particular case, the transistor doesn't need to be biased in the active region because it acts as a Class C amplifier. This type of amplifier can create high-power sine-waves much more efficiently than a linear amplifier. Since a periodic pulse contains not only the fundamental frequency component but also its harmonics, the only frequency that will appear at the antenna (and amplified) is the one that resonates the LC tank. If this is an aircoil, the transmission frequency is about 40 MHz.

In the receiver, the input transistor is force biased to the active region by the diode and feeds a high gain amplifier made by the op-amps. The capacitor at the right op-amp's non-inverting input ensures operation only for the high frequencies. Then the signal just trigers the mcu and the rest is simple software.

 

Thank you all very much for your help. I was a bit overwhelmed trying to decipher all the schematics I found. I'm going to try and build DickCapples circuits and see where I go from there.

Thank you again.