[time-nuts] OT: Power level reference

[Joseph M Gwinn]

time-nuts-bounces at febo.com wrote on 12/01/2009 07:00:21 PM:

> From:
> 
> "J. Forster" <jfor at quik.com>
> 
> To:
> 
> "Discussion of precise time and frequency measurement" <time-
> nuts at febo.com>
> 
> Date:
> 
> 12/01/2009 07:10 PM
> 
> Subject:
> 
> Re: [time-nuts] OT: Power level reference
> 
> Sent by:
> 
> time-nuts-bounces at febo.com
> 
> Scopes tend to have non-flat frequency response. I'd consider aprecision
> load and something like an HP 3400A True RMS meter for up to a 
> hunderd MHz or so.

Scopes are optimized for fidelity of waveform shape, which requires a 
Bessel response curve.

So, the response to pure tones will vary with frequency, but this can be 
compensated for mathematically.

Joe 



> 
> Above 10 MHz the HP 432A would be my choice.
> 
> FWIW,
> -John
> 
> ===============
> 
> 
> > At 11:41 PM 11/30/2009, Joseph Gray wrote...
> >>We all have our various highly accurate frequency and perhaps time
> >>references. Is there a relatively simple and inexpensive method of
> >>making an accurate RF power level reference?
> >>Joe Gray
> >>KA5ZEC
> >
> > Since you're a ham, I'll assume you're primarily concerned with the
> > simple case (50 ohm source impedance, sine wave, HF-VHF). Use an
> > o-scope to measure the p-p voltage across a precision 50 ohm load (I
> > use the Caddock thick film resistors available through Digikey, which
> > are 1%, with minimal inductance).
> >
> > The power is then W=((Vpp/2)^2)/100
> >
> > Not time-nuts precision, but good "bang for the buck," and you can get
> > better accuracy than a Bird wattmeter (which is only 5%), assuming you
> > have a decent scope. Without an o-scope, you can make a peak detector
> > and use a voltmeter, with some loss of low level accuracy.
> >
> > You asked for "simple and inexpensive." For higher frequencies,
> > different impedances, non-sine waves, the other more expensive
> > solutions are needed.
> >
> >
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at febo.com
> > To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
> >
> 
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/
> listinfo/time-nuts
> and follow the instructions there.