This question is about pros and cons of making an RF transmitter (eg in the FM band) in the classical way (eg. with a "transistor based" oscillator circuit, like this one which is very classic and simple ) or, instead, using a VCO module like this one.
About the first solution, making a transmitter with a transistor and a bunch of components, I know that most of the times, could be quite hard, the tuning of the transmitter: we have to make a precise coil, if we put our hand near the circuit the frequency will drift (also if we change the antenna length or position), and if the circuit is very basic, I guess that will also transmit some harmonics. Obviously I know that an oscillator transmitter could be more stable with some "trick": would be better make short connections (eg to avoid parasitic capacitance), we can put the circuit in a metal case (and connecting the ground to the metal case), provide a stable power supply, avoid the heating of the transistor and so on.
But I'm asking myself if starting with a VCO module would be more simple from the beginning. Taking again as example the POS-150 VCO Module I see that if I provide 7V to the V-TUNE pin the module will be tuned to 103.66 Mhz. So the main questions are here: a VCO module will assure more stability o will suffer of the same trouble of a classic transistor transmitter? Since the module is inside a metal case I guess that at least will not suffer of the frequency drifting if we put our hand near the module: but about the emiting power? Will also need a power amplifier on the output? The POS-150 claims an output power of 9.5dBm.
And just for starting to transmit a frequency, is enough just connecting the V+, ground connections, providing a clean VTUNE and connecting any kind of antenna? (eg a simple piece of wire).
Can someone explain me if a VCO module has some advantages and the correct ways to wiring it as transmitter? (will also need some external components, eg using some capacitors as filter, maybe on the power supply?)
Many thanks.
Best Answer
It will take considerable skill to make a transistor oscillator as good as Mini-Circuits can.
As a bonus, it can be frequency modulated by simply adding a few mv of signal onto the tuning voltage. The "Tuning Sensitivity" spec suggests you get close to the max 75kHz deviation for the FM band with only 10mV.
Obligatory notice : make sure that whatever you do applies with the rules for transmitting signals on your chosen band in your jurisdiction...