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

[Steve Thompson]

Not quite. They can calibrate the couplers all they like. Unless 
the directivity is high the readings are erroneous in the real 
world. The claimed directivity of their V/UHF couplers is awful 
and the data sheet contains a load of nonsense trying to explain 
why readings vary with cable length. The HF couplers are a bit 
better, but far from delivering the sort of accuracy they imply.

 From memory, HP436A measured with an accuracy of around 3%. The 
fourth digit in power reading in their prime photo is meaningless, 
the third isn't much better than 0 or 5.

Steve

> "The cable and attenuator errors can be known without error, all he has to 
> do is pay a
> cal laboratory to characterize each at the test frequencies."
> 
> I've watched the Array Solutions guys calibrate their PowerMaster couplers. 
> They use their VNA2180 to accurately measure their cables and attenuators. 
> So the only inaccuracy is the tolerance of the HP power meter.
> 
> Phil - AD5X