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Ok guys I can't understand something.

Say that I have this circuit:

enter image description here

Assuming that I apply at the antenna 5V, how can I calculate how much power I will trasmit?

I found on internet that the current that will flow on the antenna radiation resistance, but if for example I go on ebay for try to find antenna no one quote the antenna radiation resistance, so how can I choose my antenna?

Moreover I want to know what capacitor C1 and C2 do in this circuit.


marked as duplicate by Dave Tweed Jun 10 at 20:00

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  • \$\begingroup\$ The antenna will only radiate when an AC voltage is applied. So 5V DC will not work. The circuit generates such an AC voltage with some base frequency and some additional frequency deviation providedby MIC1. \$\endgroup\$ – Stefan Wyss Jun 10 at 18:42
  • \$\begingroup\$ You're overthinking this. 1) you should not apply 5 V to the antenna connection but at the top of L1 otherwise this circuit isn't going to work. 2) This is an extremely simple circuit, how much power it transmits will depend on many factors including the antenna. If you worry about "transmitted power" then you're not grasping the fact that this circuit is too simple to talk about that. 3) usually the antenna is just a piece of wire like 30 cm long. Buying an "antenna" for this crappy circuit is a waste of money. \$\endgroup\$ – Bimpelrekkie Jun 10 at 19:23
  • \$\begingroup\$ The circuit is a variation of a Colpitts oscillator, read more here: wiki.analog.com/university/courses/electronics/… But again: this isn't a serious circuit, it is a "toy" circuit. Also note that using it might be illegal in your country as most of these transmit in the FM radio band which is usually prohibited. \$\endgroup\$ – Bimpelrekkie Jun 10 at 19:24
  • \$\begingroup\$ @Bimpelrekkie in any case, if I buy an antenna which factor I have to look, that will let assimilate the antenna as resistor, so I can easily calculate the Transmitted Power? \$\endgroup\$ – student-a4 Jun 10 at 19:31
  • \$\begingroup\$ Antennas aren't "assimilated as a resistor", antennas have an impedance. But that's irrelevant here as this circuit is too simple, it does not have a proper output impedance that you can match to an antenna. You have two options: 1) You use a piece of wire (30 cm) as the antenna or 2) you study RF circuits to better understand what I'm trying to explain above. Then you'll learn that what you insist on doing now (improving the antenna) is pointless and "silly". \$\endgroup\$ – Bimpelrekkie Jun 10 at 19:38