R. Measures wrote:
>> 2) People who were wrong, and don't wish to admit it.
>
>
> chortle
It's just childishness to hang on to an argument if you know you are wrong.
There is nothing wrong with not knowing that RMS power and mean power
were the same. I have freely admitted that I'd never considered the
issue before.
Furthermore, had someone asked me, then I too would have no doubt
thought that the I_rms*V_rms=P_rms. It seems most natural to me. Others
have said it is a widely held misconception.
I know an ex-colleague of mine, went to a local HiFi shop to buy some
HiFi. The guy in the HiFi shop was giving it all the sales talk on the
power of this amplifier, thinking she was a dumb blonde. She was blonde,
but not exactly dumb as she had a PhD in physics.
So she questioned him if the power was RMS, or some musical thing with
no basis. At this point he realised she was not so stupid. But it seems
she was wrong to question if the power was RMS, but mean would have been
the technically correct term. (I'm also aware that for music, there is
some logic in having an amplifier capable of producing high peak powers
for short periods with little distortion, but not be capable of
producting such powers on a continuous basis).
But I can't help but feel it was childish to send a one worded reply of
"bananas" when I asked you to substantiate what you were saying, or find
a fault in my analysis. It would have been much better to either
a) Substantiate your argument.
b) Find a flaw in mine.
c) Admit you did not follow my maths - I would have had more respect for
you doing that, than you gained by silly one word responses.
>> 1) Relevant to amplifiers. They do produce RF power, so measuring it is
>> a pretty good idea.
>
>
> As I see it, a more meaningful measurement is what effect an amplifier
> has on S-meter readings. Experience has taught me that a 20db change
> in PEP does not always produce 20db more or less signal at the receiver.
I'd have to disagree, as personally, I would have thought the effect on
readability is far more important than what the S-meter says.
There are techniques, such as coherent detection, where you can reduce
the power dramatically, so the S-meter will not move, yet improve
readability considerably.
I know some had a theory about the non-linear relationship between
transmitted power and received power since the power from his
transmitter is affecting the ionosphere. Personally, I don't believe
it, but that is another matter.
But in order to draw any meaningful conclusions from experiments of
coherent detection, non-linear effect, you need to make measurements.
All measurements will be subject to some calibration error, but if the
calibration is based on a fundamentally flawed technique, then that is
another matter altogether.
There difference between RMS and mean power for a sine was is about
22.5%, which is not huge, but for all you or I knew it could have been
200000%.
>>
>> 2) There is a 22.5% difference between the mean and RMS values of power,
>> so the replies by some of "who cares anyway" seem odd, when there are
>> quite a few who would care about a 22% difference in power levels.
>
>
> I have conducted many tests on 40m during daylight hours where I
> increased PEP by 40%, and, thanks to QSB, so far no one has been able
> to consistently detect the change on a S-meter at the Rx end.
Agreed. But that does not mean that meters should be calibrated by a
method which is fundamentally flawed.
>>
>> 3) Within their grasp to understand.
>>
>> To follow the paper written in Laymens terms
>> http://www.eznec.com/Amateur/RMS_Power.pdf
>> you need the level of maths and electronics any radio ham should be able
>> to handle if they put their mind to it.
>>
>> To understand the formal definition of RMS (using integration) a level
>> of mathematics that I had learnt at school by about the age of 16 will
>> suffice.
>>
>> 4) A new topic discussed, and not the same old arguments being used
>> about a topic that comes up again and again, year in and year out.
>>
>> It's also possible the topic has greater implications that some of you
>> think. ...
>
> ... ... ...
> Indeed, David, indeed. I see a connection with Freudian psychohistory
Sorry I don't know what you mean by this. I done a quick web search on
Freudian psychohistory, and whilst there are 100's of documents with
both words in them, it is not too clear to me what it means. Perhaps you
can put it in Laymen's Language, as I really don't understand it.
> and also what Andy Warhol said about 15-minutes.
Well, it would not surprise me if there was something useful in RMS
power, so the discoverer of it might be famous for a little more than
the 15 minutes that Andy Warhol said everyone would be.
The well written article in Laymens language on mean and RMS power
http://www.eznec.com/Amateur/RMS_Power.pdf
dismisses RMS power as having no value. That might be a valid thing to
do, but there *might* be some point in computing it under some
circumstances.
Could an instrument able to measure the ratio of RMS and mean powers
give us a measure of distortion or some other useful parameter? Clearly
the ratio is different for sine and square waves. Does that tell as
anything useful? I suspect the answer is probably not, but that does not
mean my suspicions are correct.
Fleming has been famous for a little more than 15 minutes over this
discovery of Penicillin, which was found by his critical analysis of a
petrie dish, when many would have thrown that dish in the bin and
started again.
Critical analysis is often beneficial.
--
Dr. David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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