John Ackermann N8UR skrev: > 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?
It would, unless you are able to use a double-mixer approach of some sort such that it cancels out. I was expecting something simpler and quieter, but the usual suspect for such solutions has been quitet. A number of different approaches could be used naturally. I guess one would prefer a solution where a control loop could be created. Cheers, Magnus _______________________________________________ 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.