[Amps] Measuring RF Power

[R.Measures]

On Mar 22, 2005, at 8:16 AM, Gary Schafer wrote:

>
>
> R.Measures wrote:
>> On Mar 21, 2005, at 10:06 AM, Gary Schafer wrote:
>>>
>>> R. Measures wrote:
>>>
>>>> On Mar 21, 2005, at 9:08 AM, Gary Schafer wrote:
>>>>
>>>>>
>>>>> Tony King - W4ZT wrote:
>>>>>
>>>>>
>>>>>> Harold B. Mandel wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>> <snip> PEP is different
>>>>>>> than RMS, and RMS is different than Average. <snip>
>>>>>>>
>>>>>>>
>>>>>> It may be worth mentioning that RMS is the usual method of 
>>>>>> defining a DC
>>>>>> equivalent which, given a pure waveform, will be about the same 
>>>>>> as the
>>>>>> average. With distorted waveforms RMS will not define the average
>>>>>> properly.
>>>>>
>>>>>
>>>>> It may also be worth mentioning that there really is no such thing 
>>>>> as
>>>>> "RMS power". The proper term is average power. RMS is only valid in
>>>>> terms of voltage or current.
>>>>>
>>>>> You can find an RMS value of power but it is not useful for 
>>>>> anything.
>>>>
>>>> It's fairly useful for heating water.
>>>
>>> Only average power is useful.
>> Average power is not a measure of heating ability.  RMS power is a 
>> measure of heating ability.
>> cr
>
> That's a common misconception.
> Only RMS voltage or RMS current through a resistor produces the 
> equivalent heating that the same value DC voltage or current provide 
> into that same resistor. When calculated for power they are all 
> average power.
>
> 2 amps DC into 1 ohm = 4 watts average power.
> 2 amps RMS into 1 ohm = 4 watts average power.
>
> You can not find RMS power by multiplying RMS voltage by RMS current.

I disagree. .

> That gives average power.
>
> If you square RMS voltage and divide by resistance that gives average 
> power.
>
> If you square RMS current and multiply by resistance that gives 
> average power.
>
> 73
> Gary  K4FMX
>
>
>
>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org