Hej Ulf, On 2020-08-26 09:09, Ulf Kylenfall via time-nuts wrote: > Paul, > > A 60 MHz xtal oscillator divided by 12 and comparedwith the incoming 5 MHz. > Then there is this thing > how to acheive a good symmetrical FM injecting > the 137 Hz signal without affecting the loop filterparameters. > > Keeping the original design with modern typesof semiconductors is less > work/effort, provided that the > unit keeps working... > The A7 original design used a non selective2nd harmonic detector. And uA > 709's.That one was easy to motivate an upgrade. > > I am a bit lazy otherwise.
OK, If you do a PLL loop of 60 MHz oscillator, well then you can just inject the 137 Hz into the loop just at the phase detector, assuming it's above the PLL bandwidth. If you the PLL bandwidth is higher, then you are on a 6 dB/Oct slope, but sure, for smaller range you can just compensate with the drive level. This is a known technology to do phase-modulation. You can be pretty lazy doing it after you gone through the trouble of doing a PLL-loop. Using a higher frequency oscillator with low noise can reduce noise compared to the doubler/trippler chain. One could consider if not an even higher frequency should be considered. If one plays that game, one should also consider the strategy of synthesizing two frequencies that then is combined at 6.8 GHz, as the noise of the two signals adds. Synthesizing a single frequency would be preferred, but then again, working within the limits of the current system might just work well enough. We can improve however by leaving 60 MHz and see if we can find a more suitable higher frequency that would work equally well, as the need for low noise at higher frequencies has increased for similar enough purposes. > > As mentioned, the semiconductors that have failed > in A3 were all dated 1968. > At the time without knowing the exact types of the JFET'sI replaced them with > 2N4416 only to discoverthat that was the type HP specified in a laterrevision > of the A3. Good to know. Thanks. Cheers, Magnus _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.