[NLRS] USB Power Meter

[Doug Reed]

A quick look didn't find any similar accuracy specs for a HP
8481-series power sensor so I don't know if the USB meter is better or
worse. I can say that a HP 435 analog power meter has a rated spec of
up to 1% error in the full-scale meter reading, but that isn't the
same as error in the power sensor. But the HP spec means the USB meter
is NO WORSE than a HP 435 with the power sensor of your choice at
frequencies below 4GHz. How they compare above 4GHz depends on the
accuracy of the HP power sensor itself.

Bottom line is that the USB sensor is probably no worse than a HP 436
digital meter for accuracy. Depending on the computer, it may be a
little clumsier to use. Another way to look at it is that upgrading
from a HP 436 single channel meter to a HP 438 dual channel meter is a
matter of buying a second USB power sensor and writing software to
compare the readings from two USB ports. And if you write the software
correctly you can calibrate out any(?) test setup errors.

Personally, I'm usually more interested in relative power than in
absolute power. If I can determine relative differences in power
readings I can measure gain or adjust for peak or null. If I want to
know absolute power I need a calibrated standard of some sort and you
always have to wonder if the cal standard is correct, or more likely
how far off it is. Since none of my test equipment is within any cal
date, it is a moot point.

Over all, I think I'm favorably impressed by the USB power meter
specs. The +-1dB and +-2dB specs don't seem too impressive, but after
looking at the HP specs I could find, I'm willing to bet that spec is
probably pretty reasonable for a piece of test equipment under $200.
If I already had a HP 436 with a good power head or could buy one for
that price, I probably would. I probably would not sell my HP 435 to
go out and buy the USB power sensor. But if I was considering buying a
HP 431/432 and power sensor from a used source, versus buying this USB
sensor, I'd give serious consideration to the USB sensor, assuming I
can live within the 11GHz frequency limit and didn't need the wider
selection of power heads available for the HP.

73, Doug Reed, N0NAS.