[Amps] FW: Decent HF directional coupler for RF power meas.

[Phil & Debbie Salas]

Hi Paul - I haven't looked at the PowerMaster below 5-watts.  I don't 
believee it measures SWR much below 5-watts for that matter.  However, I'm 
curious.  I'll look at it tomorrow.  I have a Tektronix TDS-2022 that is 
NIST-calibrated.  I'll see what that indicates compared to my PowerMaster 
from 1-5 watts.

Phil - AD5X

"Phil,  Do you have a way to check the accuracy of your PowerMaster below 
2-watts?
Below 1-watt, my PowerMaster deviated substantially from the Alpha 4510,
LP-100, and a 200 MHz scope measured across a precision 50-ohm load, all of
which measured very closely against one another.  The PowerMaster showed the
typical signs of inaccuracy at low power due to diode detector
non-linearities as discussed here: 
http://www.arrl.org/members-only/tis/info/pdf/9002019.pdf

I am not stating with certainty that's the cause for the deviation with my
PowerMaster, only the behavior is identical to inaccuracies seen with other
common wattmeters using simple diode detectors.   And, as I recall, the
LP-100 and Alpha 4510 use more complex, temperature-compensated detector
designs.

Since this is the AMPS group, not too many folks here will care about
low-power results.  But I think it's important to note some limitations of
the PowerMaster that are not limitations with some of the other commercial
wattmeters.

Paul, W9AC"