[Amps] RMS VS Peak VS Average power and the Bird 43 wattmeter

[Gary Schafer]

I can see some people getting nervous already. :>)

Not being an expert either, I believe what happens is the time constant 
in the meter is setup to respond to RF frequencies. When the audio is 
introduced with an AM signal the low frequency audio envelope voltage 
swings above and below the carrier reference. The meter tends to average 
things out. As you remember the average voltage of a sine wave is zero. 
This is what it is trying to see with the modulation envelope.

On SSB there is no such envelope. It is only the rf frequencies present 
that go from zero to maximum peak.

73
Gary  K4FMX


Dennis12Amplify at aol.com wrote:
> For the EXPERTS.....,
>  
>  I have a question which I believe will combign the two most  interesting and 
> informative threads we have had going here on the reflector  for quite some 
> time.
>  
>  Why is it that a Bird 43 with a calibrated peak reading kit only  reads 
> THREE times the power for a peak reading of a 100% modulated AM  waveform, instead 
> of FOUR times the power as the textbooks all say it  should?
>  
>  Is it because the 43 is responding to a Half wave  rectified signal but 
> 'calibrated' to read as though it was responding to  something else?
>  
>  I believe I have an answer, and it is directly related to both  threads, but 
> I was hoping for some open discussion of the subject to see where  it goes, 
> and if it goes in the direction of my solution or not...
>  
>  Hint: It is a mathematical relationship between the average response  of the 
> 43's analog meter movement and the FCC's definition of power  output.
>  
> Regards,
>  
> Dennis O.
>  
>  
>  
> It is surely the best thread we have seen on this reflector in a long long  
> time. Very comprehensive, informative and lots of fun to  follow.
> 
> Thanks to all,
> Alek. VK6APK
> 
> At 08:33 PM 27/03/2005,  David Kirkby wrote:
> 
>>John and Mary Powell wrote in a different  thread:
>>
>>
>>>Is there a body of opinion out there that considers  the above subject 
>>
>>has gone on far too long, or got out of hand. To me  it appears as if 
>>academic intransigence has got in the way of the  Reflector dealing with 
>>it's core business. I noted an earlier plea for  an end to of 
>>this  uninteresting topic, which evolved from a  simple enquiry as to 
>>accuracy of the Bird 43 Wattmeter.
>> >
>>
>>>Cheers
>>>John Powell.  ZL1BHQ
>>
> 
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