Use a MV89 or something like it and lock it to the 5680A with a 10 to 100 Hz analog filter. You will like the results at 10 GHz. Bert Kehrenn In a message dated 2/7/2012 12:48:57 P.M. Eastern Standard Time, turner@ussc.com writes: Hello, As has been mentioned here before, the output of the "non-tunable" FE-5680A's has been noted to have low-level spurs in it - no doubt due to the way the various frequency loops are derived within, some using DDS techniques. It is for this reason that when I packaged my FE-5680A in its own, stand-alone enclosure I included a fairly narrow band (+/-6 kHz @ -6dBc) crystal-based bandpass filter in the output. After more recent testing of two FE-5680A's using two different 10 GHz microwave transverters, I've determined that this filtering just isn't enough. At first, it was assumed/hoped that the racket that I was hearing was coming from somewhere else - perhaps the switching up-converter or some other interaction - or just something "odd" about my homebrew 10 GHz transverter, but this is, unfortunately, not the case. In testing with a DownEast Microwave 10 GHz transverter fitted with an N5AC synthesizer, the CW notes sounded nice and clean when locked to the Z3801 and there was only a trace of modulation that I'd not really noticed before when I used the Efratom LPRO-101, but when the '5680A was connected, the incidental PM was bad enough that it was difficult to determine where, exactly, zero beat was! Since the synthesizer uses a fairly high reference frequency internally there was little impediment to the low-level phase modulation on the reference. I compared this with my own homebrew 10 GHz transverter. This unit uses an 18.4 MHz Butler VCXO that is multiplied to 110.4 MHz which is then fed to a "brick" oscillator with the 110.4 MHz being compared to the 10 MHz reference using a harmonic mixer, locking to the 400 kHz residual. Since this unit has a comparatively low loop bandwidth in the VCXO the grunge was considerably reduced, but still objectionable, giving some hope that a simple VCXO scheme might make the '5680A usable. I still have yet to do a more-detailed analysis of the phase modulation that is appearing on the 10 GHz signals, but I can clearly hear a low frequency modulation source (perhaps the lock-in amplifier) plus a myriad of other audio frequency components and their harmonics. Again, with the LPRO-101 was very "clean" by comparison and I could *just* hear some similar, very low-level noises in the background that I'd not really noticed before. As it is, the '5680A-based reference is unusable with the N5AC synthesizer and its wide loop bandwidth and "almost" usable with my homebrew transverter and its comparatively narrow loop bandwidth. I'm now bent on making the '5680A usable as a microwave reference, but my current plans are to build a simple 10 MHz Butler VCXO and then lock it to the '5680A using a very "slow" loop filter: In that way, I'm hoping that the phase noise will be largely that of the 10 MHz VCXO and its cheap CPU-type crystal rather than the '5680A! 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.