Nice job!! Rob
-----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of C. Turner Sent: 13 February 2012 21:03 To: time-nuts@febo.com Subject: Re: [time-nuts] FE-5680A's suitability for use as a 10 MHz reference for microwave transverters Last week I noted that the FE-5680A's "barefoot" output was found to NOT be a suitable 10 MHz reference for microwave transverters. Specifically, I tested it on two different 10 GHz transverters and found there to be objectionable levels of "grunge" on signals caused by low-level phase modulation internal to the '5680A and at 10 GHz the result of this phase modulation was a racket of audible and subaudible noises on CW carriers that made it difficult to find zero beat! In comparison, the 10 MHz outputs of the Z3801, Isotemp VCXO and LPRO-101 yielded results at 10 GHz that were quite clean. Related observations were also made by N8UR in his web page comparing various units. In order to clean up the output of the FE-5680A I did the obvious thing, disciplining a homebrew VCXO to its output - details are found here: http://www.ka7oei.com/10_MHz_Rubidium_FE-5680A.html While the comparison frequency is fairly high (1.25 MHz) the loop gain and bandwidth are quite low so it's pretty much the Butler oscillator VCXO that determines the phase noise of the 10 MHz output and I can't detect any audible artifacts from the '5680A at all. At the moment I don't have the means of generating a "pristine" test signal at 10368 MHz, but from what I can determine, the resulting CW notes from the transverter (being locked to the "regenerated" output of the the '5680A) compared to the other 10 MHz sources sound the same. At some point I hope to do a more-detailed analysis. Had I a low-noise "canned" 10 MHz VCXO around, I'd have probably used that rather than go through the hassle of building the oscillator, but none of the 10 MHz VCXOs that I *did* have on hand produced as good a CW note as the Butler built around a cheap microprocessor-type crystal. I also had on hand some 10 MHz ovenized VCXOs which would have worked fine, but not only were these too large to fit in the box, they would have added even more current consumption to an already power-hungry frequency source - an important consideration when operating from a battery! There are, no doubt, a number of ways one could do this same thing, but it's clear that this simple of a circuit will do an admirable job of extracting the frequency stability of the FE-5680A without the synthesis-related artifacts. Of course, the regenerated 10 MHz output will have a degree of variable phase offset with respect to the '5680A's "barefoot" 10 MHz output over varying conditions (such as temperature) but when used only as a frequency reference these rather slow changes are unimportant. 73, Clint KA7OEI _______________________________________________ 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.
