John Ackermann N8UR wrote: > Hal Murray said the following on 12/23/2008 01:58 PM: > >>> 2. Several measurement techniques require a given phase relationship >>> (e.g., quadrature) between DUT and reference. For HF frequencies (ie, >>> 5 or 10 MHz) is there a *practical* phase shifter design covering >>> 180+ degrees that doesn't involve switching various lengths of coax >>> in and out of the line? >>> >> PLL up by a factor of N, use that to drive a DDS, then filter. Maybe a pair >> of DDSes will get better tracking. >> >> For each possible phase offset, you need N slots in the table. (N/4 with >> more work) >> > > If doing phase noise or short term stability measurements, wouldn't the > noise of the DDS impact the results? > > John
Split the signal to be measured, use 2 independent DDS circuits, 2 mixers and measure the cross power spectrum of the 2 mixer outputs. This should only measure the noise common to both channels. Should be easy to do with a sound card for example. The phase noise of other non common components such as isolation amplifiers should also cancel. Bruce _______________________________________________ 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.
