Hi For a one time frequency response check, a directional coupler and a signal generator do a pretty good job of creating a useful test tone.
Bob On Aug 24, 2010, at 4:03 PM, Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote: > Having a simple method of determining the preamp frequency response can be a > useful diagnostic tool during development, particularly if one uses componets > like super capacitors in the amplifier signal path. > > If one doesnt have a suitable offset source handy the mixer ports can be > driven in near quadrature by the same signal and the dc output as a function > of the relative phase shift between the 2 mixer inputs can be used. > > However neither method calibrates the phase noise frequency response of the > system. > Adding RF noise to one of the mixer inputs can be used to measure the > frequency response of the system. > If the RF noise source is uncalibrated but stable then it can be used to > measure the relative frequency response. > The results of a dc (or beat frequency) measurement of the gain can then be > used to correct the results to obtain a calibrated frequency response. > > If one is using a capacitive or other non conventional mixer IF port > termination, then knowing the relative frequency response can be vital. > > Bruce > > Bob Camp wrote: >> Hi >> >> I've always calibrated my phase noise setups to the phase slope of the mixer >> I'm using. It does involve switching gains, but it's a direct system >> calibration. Beat note is 360 degrees, so this chunk is x degrees and you >> got y mv over that chunk. Check the slope on the other side of the beat note >> to make sure it's the same. Do some math and you have a radian to volt >> transfer function. >> >> If you are sorting junk box OCXO's it's a pretty good way to do it. The only >> added steps are an independent measurement of the switched gain / gain >> flatness and a short circuit input check to estimate the noise floor. Both >> are an initial setup / one time only sort of thing with most amps. >> >> Bob >> >> -----Original Message----- >> From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On >> Behalf Of Bruce Griffiths >> Sent: Tuesday, August 24, 2010 3:25 AM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] Phase noise measurement (was - no subject) >> >> Bob Camp wrote: >> >>> Hi >>> >>> >> < CHOP> >> .... >> Being able to calibrate the preamp + sound card frequency response using >> the thermal noise of a resistor is convenient. >> This is more difficult to achieve with a bipolar input stage as the >> amplifier input current noise is significant. >> >> Bruce >> >> >> > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@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@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
