[time-nuts] SMD TADD-1 distribution amplifier - seeking comments and suggestions?

Anders Wallin anders.e.e.wallin at gmail.com
Thu Dec 17 14:44:27 EST 2015


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 <bruce.griffiths at xtra.co.nz
> 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 <
> anders.e.e.wallin at gmail.com> 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 -- time-nuts at 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 at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



More information about the time-nuts mailing list