[time-nuts] OT: Power level reference

Bob Camp lists at cq.nu
Wed Dec 2 22:39:27 UTC 2009


Hi

I think that spending some time with a *good* reflection bridge at the specific frequencies of interest would be time well spent. 

Of course that heads us of to the subject "OT: 50 ohm Standard Reference". I have some nice HP cal kits running around, but none of them really agree with each other without going back to the calibration data. For low frequencies you can do pretty well with a set of precision thin film SMT resistors. They fall apart as frequency heads up past a few hundred MHZ. 

Bob


On Dec 2, 2009, at 7:47 AM, Poul-Henning Kamp wrote:

> In message <BA422CF5-53F0-443C-8AD1-EDC91A58464A at cq.nu>, Bob Camp writes:
> 
>> The accuracy / flatness of the detector is only one part of the problem. 
>> 
>> In an RF system, the match to the detector can be a significant
>> part of the error. If some of the power is reflected it messes up
>> the reading ....
> 
> No disagreement from here on that.
> 
> What I played with, was a 50 Ohm termination a rotating mechanical
> shutter and a IR sensor to see if it would be possible to level
> three different frequencies to the same power-level, for calibration
> of a HP3458A.
> 
> For this particular _relative_ power measurement, I think
> the method has merits, it it may be possible to use it
> to calibrate relative to DC as well, thus making the
> calibration absolute, but I need to work on the mechanical
> setup some more.
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
> 
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