# What Is The Power Output Of A Radio Transmitter?

#### Glenn Holland

Joined Dec 26, 2014
698
This question should have been posted in the physics section, but someone in the RF business might know the answer.

The energy (E) in a single photon is E = h X f where h = Planck's Constant and f = the frequency of the individual photons in a stream of electromagnetic waves.

So if a radio transmitter is outputting electromagnetic waves (photons) of a given frequency (F), then it seems the power would be the energy per photon X the number of photons/second. Therefore the power would be proportional to the square of the frequency.

#### crutschow

Joined Mar 14, 2008
24,125
Therefore the power would be proportional to the square of the frequency.
Only if you are radiating the same number of photons.
As the frequency increases, a smaller number of photons is radiated for a given radiated RF power.

• sagor

#### MrAl

Joined Jun 17, 2014
6,977
This question should have been posted in the physics section, but someone in the RF business might know the answer.

The energy (E) in a single photon is E = h X f where h = Planck's Constant and f = the frequency of the individual photons in a stream of electromagnetic waves.

So if a radio transmitter is outputting electromagnetic waves (photons) of a given frequency (F), then it seems the power would be the energy per photon X the number of photons/second. Therefore the power would be proportional to the square of the frequency.
Hello,

If we have 10 photons at point A each with energy of 1 unit and they move to point B, point B then has 10 units of energy and A has none.
Now if we increase the frequency of another 10 photons at point A to 2 times the previous the energy of the 10 photons is now 20 units. Now when the 10 photons move to point B then point B has 20 units of energy. In the second case the energy increased by a factor of 2 (twice the frequency) so the energy was proportional to frequency.
So how do you get more energy out of a photon just because it moves to a different place?

A beam of photons has power:
P=Phi*h*f

and when we increase frequency f by a factor of 2 the power P increases by 2.
The only way to get more power than two fold is to increase the flux Phi which means more photons per second have to be emitted in the beam.

I am not sure i understand what you are getting at entirely though. It sounds like you are suggesting that the photons can somehow move faster than light.

#### KL7AJ

Joined Nov 4, 2008
2,225
Planck's constant is such a teeny tiny little number that at "normal" radio frequencies, we don't even talk about photons....though we theoretically could. Unlike at atomic wavelengths where energy is proportional to frequency....at very long wavelengths amplitude and frequency are two very different things.