Hi Vic,
Vic K2VCO wrote:
> ...does the +/- 0.5 db accuracy of the W1 mean 0.5 db of full scale,
> or 0.5 db of the reading?
>
> So if I am measuring a 5 watt signal, is that 0.5 db of 5 watts or 0.5
> db of 14 watts?
The former. Here's the long answer (from the designer of the W1, Bob,
N6CM):
The accuracy of the W1 is determined by two factors: the underlying
accuracy of the directional coupler and detector system, and the
resolution of the display. When used with an attached computer and the
supplied software, the W1 accuracy is typically within 0.5 dB of the
displayed (not full scale) power. This is more accurate than most
available power meters. If a more accurate power meter is available,
then even this error can be reduced by adjustment of the CAL control.
When used with the built in bar graph display, the accuracy can degrade
due the resolution possible with the 10 LEDs that make up the bar
graph.
The bar graph is calibrated so that a LED just lights at its marked
power. So, when setting transmit power, if the operator increases
power until the desired power is first displayed, the 0.5 dB
specification applies. However, as the power is further increased
additional error is introduced until the next LED lights. For example,
if we consider a case where the error in the accuracy of the
coupler-detector system is zero and we are adjusting to 5 watts, the 5
watt LED will light when the power reaches 5 watts and the error is
zero. If the power is further increased to 5.9 watts, the 6 watt LED
will not yet be lit and the error introduced by the resolution of the
display is 0.72 dB. As the power is increased to 6 watts, the 6 watt
LED will light and the error is again zero.
73,
Wayne
N6KR
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