First prototype assembled today, tested with 12 VDC SMPS wall-wart supply and with 12 V lead-acid battery. Compared against a SRS FS710 and a Symmetricom 6502 and John Ackermann's 2007 plot: http://www.anderswallin.net/2015/12/frequency-distribution-amplifier-first-tests/
What does the 6502 do differently? It is maybe 5 to 8 dBc/Hz better both in PN and AM from around 1 kHz and out. My 'ultra-low-noise DC-supply' in the form of a lead-acid battery improves things somewhat, but some spurs still remain: http://www.anderswallin.net/wp-content/uploads/2015/12/2015-12-17_fda_spurs_and_comments.png interpretations and explanations are welcome! The board was not enclosed in a metal can for these tests. The regulator is an LP38798 http://www.ti.com/lit/ds/symlink/lp38798.pdf Anders On Tue, Dec 1, 2015 at 12:54 AM, Bruce Griffiths <[email protected] > wrote: > Anders > U101 only needs to have a gain of 1 at dc so replace R104 and R105 with a > capacitor connected to ground. > Adjust the other components of the gain determining network > accordingly.Also the junction of the power supply divider R102 and R103 > should be heavily capacitively bypassed to ground and a resistor placed > between this junction and U101's noninverting input. > > Excess Sub Hz PN is usually due power supply noise or thermal fluctuations > due to air currents/ convection. > Most of the so called super regulator circuits should be more than quiet > enough with an LM329 reference.A damped LCR filter at the input will > improve the PSRR at switchmode output frequencies. > > Bruce > > > > On Tuesday, 1 December 2015 9:02 AM, Anders Wallin < > [email protected]> wrote: > > > HI all, > I need to build a few distribution amplifiers (>90% for 10MHz, sometimes > maybe 5MHz) and instead of reinventing the wheel I decided to try to > modernize the TADD-1 into an all (almost) SMD design. Here are some draft > sketches: > > http://www.anderswallin.net/2015/11/frequency-distribution-amplifier-plans-a-k-a-smd-tadd-1/ > > Does this sound/look reasonable or crazy? > Any suggestions for op-amps to try and/or compare to the AD8055? > What causes the extra phase-noise below 1 Hz offset in John A's result: > https://www.febo.com/pages/amplifier_phase_noise/amplifier_phase_noise.png > > Suggestions for a low noise DC-regulator circuit? The 12-24VDC supplied to > this board will most likely come from a switched-mode PSU, so filtering of > common-mode noise is mandatory. > I found the TI LP38798 shown in the schematic by googling - if someone has > a proven a measured design that would be a safer choice. In any case more > filtering (e.g. ferriites) is probably a good idea. > > This design will be available on my blog or on github when it is done - if > anyone is interested. > > Thanks, > Anders > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
