In a message dated 1/5/2008 16:58:01 Pacific Standard Time, jmiles@pop.net writes: >That's a good point; how are you (Said) calibrating the system? >For simplicity I'd drive the mixer's LO port at its full spec and start with >the RF port unsaturated, at (presumably) 0 dBm. Hi John etc, I've been reading all the posts and greatly appreciate the help. I may end up getting a 11729C, these seem to be reasonably priced. I've tried two ways to calibrate my setup: one was to detune the OCXO's by >20Hz, and measure the resulting beat frequency level. Another was to use our FireFox signal generator to add a 10.0001MHz signal -30dB below the carrier into the DUT output using a power combiner, and measuring the resulting 100Hz spur. Both methods result in output spurs that are within <2dB of expected. I will try the hints from everyone, thanks, Said **************Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489

SAIDJACK@aol.com wrote: > In a message dated 1/5/2008 16:58:01 Pacific Standard Time, jmiles@pop.net > writes: > > > >> That's a good point; how are you (Said) calibrating the system? >> > > >> For simplicity I'd drive the mixer's LO port at its full spec and start with >> the RF port unsaturated, at (presumably) 0 dBm. >> > Hi John etc, > > I've been reading all the posts and greatly appreciate the help. I may end > up getting a 11729C, these seem to be reasonably priced. > > I've tried two ways to calibrate my setup: one was to detune the OCXO's by > >> 20Hz, and measure the resulting beat frequency level. >> > > Another was to use our FireFox signal generator to add a 10.0001MHz signal > -30dB below the carrier into the DUT output using a power combiner, and > measuring the resulting 100Hz spur. > > Both methods result in output spurs that are within <2dB of expected. > > I will try the hints from everyone, > thanks, > Said > > Said Another issue to consider is mixer dc offset and mixer induced phase shift. Both of these effects will cause the PLL to lock with the RF and LO signals not in exact phase quadrature (unless the correct dc offset is used at the PLL input amplifier). The phase relationship between the RF and LO signals at lock is easily determined with a time interval counter or an oscilloscope. When selecting a mixer low dc offset is desirable however this is usually not stated in the datasheet except for those mixers specified for phase detector operation. However the dc offset can be estimated from the mixer port to port isolation specs see: http://www.wj.com/documents/Tech_Notes_Archived/Mixers_phase_detectors.pdf There are also other effects such as mixer induced phase shift which can be more significant at higher mixer input frequencies. The ideal is to adjust the mixer operating point to minimise its AM sensitivity, this doesn't necessarily correspond to phase quadrature between the RF and LO signals at the RF and LO ports. Saturating both mixer ports can help minimise its AM sensitivity. Bruce