[email protected] wrote on 12/01/2009 07:00:21 PM: > From: > > "J. Forster" <[email protected]> > > To: > > "Discussion of precise time and frequency measurement" <time- > [email protected]> > > Date: > > 12/01/2009 07:10 PM > > Subject: > > Re: [time-nuts] OT: Power level reference > > Sent by: > > [email protected] > > 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 -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/ > listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
