[time-nuts] OT: Power level reference

[Bruce Griffiths]

Since a  levelled generator requires a detector with a flat frequency 
response, calibrating a scope so that it can in turn be used to measure 
power is a somewhat circular process.

In the 1970's NBS used a matched pair of schottky diode detectors 
mounted in the same temperature controlled heatsink to compare RF and dc 
signals.

David C. Partridge wrote:
>> 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!
>>      
> I think you may find the option was best pulse response OR an increased 3dB
> frequency of 275 MHz.   The difference is just an matter of adjusting the
> compensation in the vertical amp.   The best pulse response in terms of
> least overshoot etc, also gives a flatter response in the pass band (which
> it should as this is effectively adjusting to give a pure Bessel response).
> The higher 3dB frequency version gave considerable overshoot on the pulse
> response, and a "bumpier" pass band.
>
> I was quite surprised to find quite HOW bumpy the pass band can be the first
> time I did a check on my 7904 using an SG504.
>
> Dave
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of J. Forster
> Sent: 02 December 2009 01:31
> To: Mike S
> Cc: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] OT: Power level reference
>
> 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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