[time-nuts] OT: Power level reference

[Bob Camp]

Hi

Boonton has made power meters (RF milivolt meters to be more precise) for a long time. They also make a calibrator for them.

If you tear into the calibrator, it's a very simple gizmo. They take the output of a buffered logic gate and feed it into a big low pass filter. A few resistors / pads here and there keep things from getting to crazy impedance wise. 

You can do pretty much the same thing with a cheap clock oscillator and a good set of buffer gates. Supply the gates from a very accurate supply and the square wave is going to be very predictable. The main gotcha is to not load the output to heavily. No direct drive into 50 ohms, no giant capacitors to ground ....

The same approach works for a low level signal source. They can be very useful to check calibration on things like signal generators and spectrum analyzers. 

Bob


On Dec 1, 2009, at 8:30 PM, J. Forster wrote:

> I do. Very well, in fact.  Unless you have swept a scope with a very well
> leveled sine generator, you are only guessing it is flat.
> 
> That's WHY Tektronix sells BOTH fast rise Pulse Generators and Leveled
> Sine Generators.
> 
> In fact, on the Tek 7704 or 7704A (I forget which) there were "No Cost"
> options of maximally flat frequency response OR best pulse response. OR!
> 
> -John
> 
> ================
> 
> 
>> At 07:00 PM 12/1/2009, J. Forster wrote...
>>> Scopes tend to have non-flat frequency response. I'd consider a
>>> precision
>>> load and something like an HP 3400A True RMS meter for up to a hunderd
>>> MHz
>>> or so.
>> 
>> You have to know your equipment. I have a Tek 485 350 MHz analog scope,
>> so I'm confident it's flat into VHF (at least beyond 100 MHz). I've
>> verified it exceeds the 350 MHz spec (i.e. < 3 db down @ 350 MHz) with
>> a tunnel diode pulser.
>> 
>> 
>> 
> 
> 
> 
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