# Relationship between transmitter power and electrical characteristics of the signal

#### Denesius

Joined Feb 5, 2014
124
A question came up regarding transmitter power. If one were to compare (by measuring with an AC voltmeter) the signal at the antenna output of 2 transmitters, same frequency (say a simple sine wave at 150 MHz), one putting out 1 Watt, the other 10 Watts:
Since the frequency is the same, the only remaining variable is the RMS voltage. Is there a way to calculate what that would be for any given power output?
Will the voltage be 10 time greater for the higher power transmitter, or are there other determining factors?
Will the voltage be the same for transmitters of equal power, but different frequencies?
Finally, does the 50ohm transmission line impedance have any role in determining the measured voltage, if it were to be measured at the antenna input versus the transmitter output?

#### BobTPH

Joined Jun 5, 2013
6,074
Do you know the relation of power vs voltage into a fixed impedance?

For instance calculate the power of V volts into R resistance. If you can do this, you can answer your question.

Bob

#### joeyd999

Joined Jun 6, 2011
4,625

#### Denesius

Joined Feb 5, 2014
124
BobTPH:
The voltage is what I'd like to determine. The power is given, but the current is also an unknown. Resistance can't be as simple as the output impedance, since that changes with frequency.

#### Denesius

Joined Feb 5, 2014
124
Joeyd999:
I'm not interested in the radiated power, which has many variables. The question is: what is the relationship between the output power and expected voltage at the transmitter output, before line and antenna impedance and losses come into play?

#### MrChips

Joined Oct 2, 2009
27,670
...one putting out 1 Watt, the other 10 Watts:
Will the voltage be 10 time greater for the higher power transmitter...
Do the math.
Power = V x V / R

Bob gave you a hint:
Do you know the relation of power vs voltage into a fixed impedance?
For instance calculate the power of V volts into R resistance. If you can do this, you can answer your question.
Bob