275 watts may be correct, under two conditions, (1) The Bird Wattmeter
is a peak wattmeter, and the peak reading button is pressed in. (2)
The actual output of a class C modulated final (s) modulated by a
class B modulator is four times the carrier power.

Just a remark on Bird wattmeters:

- it is true that a peak wattmeter will correctly show the peak power of a 100%
amplitude-modulated carrier (4 times the unmodulated carrier power)
- conversely, a normal (i.e. non-peak) wattmeter will NOT correctly measure the
average power of a carrier 100% amplitude-modulated by a sinusoidal tone (that
is 1.5 times the carrier power).

Reason is that the (non-peak) wattmeter actually measures the average voltage
of a rectified RF signal sample and displays the measurement result in terms of
RF power by the use of a non-linear (quadratic) meter scale.

The average voltage of the rectified RF signal does not vary when modulation is
applied, as the positive peaks are perfectly compensated for by the negative
peaks. Such compensation does not instead occur with regard to RF power, as the
positive-peak power is, as already said, 4 times the unmodulated carrier power
and not just 2 times.

In conclusion the Bird wattmeter (and all other wattmeters working on the same
principle) will show the same RF power, independently of whether the carrier is
modulated or not. And that is clearly wrong.

Only measurement devices that actually measure RF power (e.g. bolometers) will
correctly show the modulated carrier power.

73

Tony I0JX