How to build a transmitter using a VCO module

Question

this question is the consequence of my previous questions, since I am learning how RF transmitters works. In past I have also built some oscillators (using little transistors and a bunch of components), but now I wish to use a VCO module.

Please also consider that obviously I follow and respect the jurisdiction about the power of these transmitters, firstly because I don't wanna infringe the laws (where I live, in Italy, we can however quietly use low-power transmitters) and last but not least, because I don't need to transmit high power. I also bought a spectrum analyzer and I have fun to learn and see that the circuits that I build are able to give me a signal that I can practically see with this new instrument.

Well, I am interested to build an RF transmitter using a VCO module (this one): for now, for me will be enough and satisfying just to measure and check the output using the spectrum analyzer: I don't want modulate any kind of input signal (eg audio or voice). Looking at the datasheet I can see the pinout: 3,4,5,6,7 to ground, 1 is for VCC, 8 for V-TUNE and 2 is the output.

My plans, for now, are to buy this VCO module and solder it on a common matrix board: then, using some wires, make the connections (grounds, VCC, V-TUNE and another piece of wire as antenna): in this simple way I can expect to see something on my spectrum analyzer? Or I will need some external components? (eg a capacitor to filter the power supply - However I plan to use a battery). And what about the power/distance? The POS-150 claims a power output of about 9 - 9.5dBm. I will also need a particular antenna or a simple piece of wire will be enough? Eg I know that the length of the antenna is related to the frequency that I aim to transmit, and if I go higher with the frequency, there will be the need for short connections on the board, right? And I will also see some harmonics?

Consider that I am a novice and I wish to learn; so would be fine give me a detailed answer for every point (If will be enough make simple connections with wire on the matrix board, using or not extra components, which kind/length of the antenna, which distance of transmitting I can expect and if I will see some harmonics) and obviously any explanation/consideration/advice/tricks.

Many thanks.

Answer 1

An antenna needs to be some fraction of the wave length of the signal being transmitted or received. Quarter length, half length or single length work the best. A wire should work just fine at the beginning.

To calculate the wave length the formula is Speed = Length X Frequency. Radio waves are regarded as moving at the speed of light 2.997 meters/second.

I'm not an RF guy but all of the RF equipped boards I've dealt with recently have a series capacitor in the path between the transmitter and antenna.

The oscillator itself is going to need some bulk/decoupling capacitance at the power input across VCC and GND. A mixture of aluminum and ceramic capacitors is best, at least one of each and as close the the oscillator as possible.

Finally don't let the V-Tune pin float. At the very least use a potentiometer between VCC and GND and connect the output of the pot to the V-Tune pin.

Good luck.