Bruce Griffiths wrote: > Esa Heikkinen wrote: > >>> Since retrofitting an improved oscillator circuit isn't really an option >>> you will need to filter the output to reduce the harmonic content. >>> Try a bandpass filter driven by the buffer and terminated in 50 ohms. >>> >>> >> Well I have to decide what to do, get another oscillator or try the >> filtering. The difference to another oscillators (like tbolt ocxo or >> LPRO) is so huge that I do not know how hard it would filter the 10544A >> to the same level, which parts to use and how much it will cost. >> >> >> >>> Should you retrofit an improved oscillator circuit you may as well >>> replace the oven controller to eliminate the oven switching frequency >>> related sidebands. >>> >>> >> Infact the switcher sidebands are now gone: >> http://www.amigazone.fi/files/gpsdo/544-13.png >> http://www.amigazone.fi/files/gpsdo/544-14.png >> >> It was like thios earlier: >> http://www.amigazone.fi/files/gpsdo/544-1.PNG >> http://www.amigazone.fi/files/gpsdo/544-2.PNG >> >> It was easier than I expected... When I took the output directly from >> OSC pins without using the coax connector like you suggested the >> switcher peaks was gone! >> >> So I had a closer look to the PCB today and noticed that it has only 2 >> layers and the ground net is too thin and goes around PCB totally wrong >> way so that switcher current seems to flow via the signal flow. It's PCB >> layout design fault, I think that with correct layout design this could >> be done even with 2-layer PCB correctly. >> >> But this is not a problem of course because I will design my own PCB for >> the final system anyway, having SMA connectors for 10 MHz and EFC. I'll >> also create separate power supply for ovens and signalling stages. >> >> >> > Esa > > The switcher sidebands will still be there, they are just buried in the > spectrum analyser noise floor. > > Does the board use the recommended LC filters and regulator for the > oscillator supply as depicted in Figure 3 on the 10544A data sheet? > > Reducing the harmonics by 40 dB shouldn't be too difficult. > However any amplifier after the filter will need to be carefully > designed to keep the distortion below -60dBc. > > Its better to use a multi section LC filter rather than trying to do it > with a single LC filter. > The filter phase stability will be better with a multi section LC filter. > > Alternatively you could use a bandpass filter combined with some series > tuned shunt LC circuits to short out the 2nd and 3rd harmonic components. > > The required parts shouldn't be too expensive, however you may need to > wind your own inductors for the series tuned LC circuits. > Air core or powdered iron core inductors should be OK as long as you use > shields between filter sections etc. > > > Bruce > > _______________________________________________ > 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. > > Esa
Another option (which I used several decades ago with a 10544A) was to use a double tuned critically coupled RF transformer driven by a unity gain buffer with another unity gain amplifier buffering the output across the secondary tuning capacitor. NB the Q of the primary and secondary tuned circuits should be the same (need to insert a resistor in the secondary to set the Q). The inductors were hand wound and trimmer caps were used for tuning. Bruce _______________________________________________ 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.