>
>> Tom said:
>> > A good meter is more reliable than a scope.
>> What does that mean? Meters have a longer MTBF than Oscilloscopes?
>
>Well, they do but that isn't what I meant.You are supposed to read
>peak envelope power, a good meter will store the highest crest that
>comes along.
>
>It's incorrect to think you need to look at one cycle, or that a meter
>can't catch and register the envelope accurately. The rise time and
>fall time of the envelope is extended by the bandwidth of the
>transmitter. You have at least a few thousand RF cycles to
>"capture" the peak over, not just one.
>
>If we assume the highest modulating frequency is 3500 Hz with a
>sine wave (can be square, or it won't go through the SSB filter) the
>time from start to full to zero is 1/7000 second. The storage
>system in the meter has half the full rise time of that gradual slope
>available to charge the storage capacitor.
>
>1/14000th of a second is not real fast.
>
>> The waveform envelope is limited by filters to 3000 Hz, an audio limit.
>> But does not the FCC regulations state that the power is to be measured
>> over one RF cycle? At 30 Mhz = 33.3 nano-seconds At 1.8 Mhz = 555
>> nano-seconds
>
>FCC regulations say no such thing. You have 128 full RF cycles on
>160 meters to build charge to the peak, and over 2100 RF cycles
>on ten meters.
>
>The amplifier itself can not go from zero to full power in 555
>nanoseconds or less, let alone the restricted BW of the transmitter.
>
>> rectifier time-constant is 40 micro-seconds, then in 3 time constants most
>> of the prior information will be bled off and the circuit will be ready
>> for the next pulse. Some of the circuits I have looked at had 15
>> millisecond time-constants. Somehow either I am missing something very
>> simple or my logic is faulty! I think Rich is using a good system. The
>> bandwidth of the scope is more than adequate and will not miss in-between
>> pulses. The FCC says power is measured over one RF cycle.
>
>Where does it say that? They say peak ENVELOPE power, not
>cycle by cycle power.
>
? Oscilloscopes can be used to measure peak amplitude of virtually any
waveform. Peak amplitude of the RF sinewave and peak envelope amplitude
are the same thing. .
>Even if they did, what would it mean anyway?
? Knowing peak RF amplitude means that you can calculate PEP - provided
that you know R and you can remember that P=E^2/R. . .
> Even your amplifier
>can't respond that fast! If you had a nanosecond time frame
>envelope peak, your signal would be many megacycles wide.
>Violating a power rule would be the least of your worries with a
>signal like that!
? The calibrated 'scope is used to measure peak voltage of the RF
sinewave.
>
>When the FCC measures power, they use a regular peak reading
>meter. .....
? wanna guess how such meters are ultimately calibrated?.
- cheers
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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