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# Determining AM transmitter power output

#### Lajči Revaje

Mar 19, 2020
4
How do I measure/calculate the power output of an AM transmitter?

#### davenn

Moderator
Sep 5, 2009
14,085
or just buy a RF power meter

#### Nanren888

Nov 8, 2015
623
If you buy a meter, such as a bird, some measure power into a load, so you need to installl them in line, with a matched load, or the normal load, eg antenna.

#### Lajči Revaje

Mar 19, 2020
4
Acknowledging my current situation, buying or building an RF power meter seems like a bit of an overkill. However, I may consider doing either or both in case I get myself a normal transmitter with the intent of using it regularly. I happen to own a certain type of low power transmitter which I don't use for obvious reasons but I'm still curious what is its power output anyways. The said transmitter would need to have an inductive coupling installed because otherwise putting anything conductive across the output would short the transmitter power suply, resulting in false reading at best or a damaged meter.
So for now, is there a way how to calculate the power without directly measuring it?

#### duke37

Jan 9, 2011
5,364
You could measure power in and then estimate an efficiency of say 50%.
Put the power into a dummy load such as a Heathkit cantenna and measure the rate of temperature rise. Put DC into the camtenna and adjust the voltage to get the same rate of temperature rise.

It is a strange transmitter which will not take a 50Ω load without shorting.

#### Lajči Revaje

Mar 19, 2020
4
You could measure power in and then estimate an efficiency of say 50%.
That would give me an estimated output power of 0,04314 W for the little transmitter. I also put together a more powerfull version of it, with which I briefly experimented back in 2019, and measured it's input power at 1,03056 W, giving the estimate of 0,51529 W at the output. I then disassembled it immediately, again for the same obvious reasons. I don't know if these figures are mediocre or laughable. Just to give me a sense of scale, could anyone, please, tell me what commercially available transmittes (or RC controllers or Wifi routers or whatever) operate at these power levels?

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