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

Tim Shoppa tshoppa at gmail.com
Fri Dec 18 18:33:55 EST 2015


All the inputs and outputs were deliberately transformer isolated. Why
break the isolation by using capacitor from coax shield to chassis ground?

I do realize that some isolation transformers have "extra floating turns"
to give transformer action that cancels stray capacitive coupling. I don't
think the capacitors tying coax shield to chassis ground can serve that
purpose.

Tim N3QE

On Mon, Nov 30, 2015 at 3:02 PM, 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
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