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@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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>
>
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