as you know the directional power meters like NAS from R&S and many others need to be connected to proper load for their correct measurement. If you have the Insertion units (Directional coupler) loaded incorrectly (different impedance from the nominal system impedance) then the detector + following RF voltmeter will be showing incorrect values.
As I would like to arrange as precise as possible RF power measurement setup in my lab using the calibrated (NIST) NAS Directional Power Meter NAS from R&S, see over here...
so I need to use also precise and characterized dummy load for that setup.
The first candidate in the lab was an Alusid 50Ohms/1-30MHz/500W dummy-load from S. Hari, DK9FN which I used for rough checks of the different trasmitters for several years in shack.
There are the results...
I used ENA Analyzer E5061B from Agilent Technologies with full range NIST calibrations. The calibrations are valid until 18.12.2016 and according to the calibration certificate all the values are SWT (distinctly in tolerance <=20% of tol.) with no Fails.
Equipment: ENA E5061B, Port 1, 50Ohms system impedance, 50Ohms jumper RL=>35dB, 1pc of N-PL adapter used, DUT Alusid dummy-load Hari 50Ohms/500W.
Remarks: This first measurement was done with NO coaxial jumper + N-PL adapter compensation.
Ambient temp: (23.0 +/-5)deg C
Relative hum: (45 +/-25)%
All certificates for national etalons are available.
The SWR measurement done for 1 - 30MHz range.
The Z measurement done for 1 - 30MHz range in Smith diagram.
The Z measurement in R +/- jX (Ohms) units for 1 - 30MHz range.
The Return loss in Log mag for 1 - 30MHz range done.
Unfortunately this dummy-load seems to be usable for lab RF power measurement up to 7MHz only... The RL is bad for frequencies above the 10MHz and even useless for 24/28MHz ham radio band.
There you can see complete test setup on the bench in lab.
After the characterization of this dummy-load I decided to remove it from the test equipment setup (it will be used just for TX check or not measuring applications up to 20MHz/500W out) and I have to find better one...
Also I will repeat again the same measurement with coaxial jumper + N-PL adapter full compensation (there is the ENA procedure to be used) but as the RL of the jumper itself is high enough I do not believe that the results will be much different.
The uncertainties were not calculated for these values yet.
73 - Petr, OK1RP