[time-nuts] OT: Levelled sine wave generator

Lux, James P james.p.lux at jpl.nasa.gov
Mon Dec 15 14:27:03 UTC 2008


>
>>>>> David C. Partridge wrote:
>>>>>
>>>>>
>>>>>> Sort of related, but only just - however the signal to noise ratio here
>>>>>> is
>>>>>> so good that I feel impelled to ask.
>>>>>>
>>>>>> For 'scope calibration I'm considering building a levelled sine wave
>>>>>> generator.
>>>>>>
>>>>>> Ideally the specs I'm looking for are:
>>>>>>
>>>>>>  o Close to DC (10kHz or 100kHz would be fine) up to at least 1GHz.
>>>>>>     more would be better but not critical
>>>>>>
>>>>>>  o Output levels from 0.5Vp-p(-2dBm) to at least 4Vp-p(+16dBm) into 50R
>>>>>>      (up to >6Vp-p(say +20dBm) would be better)
>>>>>>
>>>>>>  o Output flatness levelled within 2% of desired output level (+/-
>>>>>> 0.086dB)
>>>>>>     across the entire frequency range at the final connector to the DUT
>>>>>>     This will almost certainly mean an external levelling head.
>
>

This is somewhat of a challenge.  Have you considered the issue of the
mismatch? Are you leveling the "forward power" or the "total power" or
something else?

Over the past 10 years, I've been involved in several projects where I was
trying to very accurately measure or generate an RF power, typically with an
uncertainty (2 sigma) of better than 0.05 dB.  It is not easy, particularly
at microwave frequencies.

Not only do you have to stabilize your output, but you need some way to
calibrate it.  Fortunately, you're in a fairly high power application, so a
variety of calorimetric measurement schemes will work, which is nice,
because they tend to be pretty broadband (getting a resistor and mounting
hardware that's flat across a band is a lot easier than a diode...).

You might want to hunt down an IEEE Proceedings from about 30 years ago.. A
special issue on RF measurements or test equipment.

Jim




More information about the time-nuts mailing list