[GPS_Standard] VE2ZAZ

[Bob Bownes]

Sounds about like what I have except the 24V for the oven is fed from
the switcher because I can't get 24V otherwise w/o building a new
supply. Interestingly enough, the switcher uses 79xx regulators on the
-tve side.

The amount of trouble I could save by moving my test bench/shack all
of 20' on the Z axis nearly makes the move worth it. But I'd miss the
sunshine. :)

Debugging a bad oven will be problematic without a spare and I'm
reluctant to spend the $80 for a new 10811 on ebay. I suppose I could
use one out of one of my tek counters, or better, modify it to take a
correction input...Hmmm. Yet Another Project.



On Wed, May 26, 2010 at 9:10 PM, Dave Platt <dplatt at radagast.org> wrote:
> Bob Bownes wrote:
>> Indeed, I'm shocked at how temperature sensitive this oven is. If,
>> after trying some of Dave's methods and tests, I find the oven is
>> good, I suspect I will be placing everything in a very temperature
>> stable environment, possibly thermally bonding it to a Very Large
>> thermal mass, aka a 12" thick concrete slab ~90" below grade. :)
>
> Maybe you could adopt the approach of the Icecube neutrino
> observatory... a cubic kilometer of Antarctic ice ;-}
>
>> What are words of wisdom on a power supply? I have dozens of switchers
>> about that will do the job, but what of any noise?
>
> If you're going to use a switcher, I'd recommend having additional
> filtering and (if at all possible) linear pre-regulation, before
> you let the power near any of the components in a frequency standard
> of this sort.  Don't put switcher-regulated power directly into
> any of the boards or oscillator, for just the reason you cite -
> noise.
>
> My own box does use a switcher (originally for a Sony laptop)
> which delivers up to around 2 amps at 16 VDC.  Its output seems
> relatively clean, but I don't really trust that.  Immediately on
> input to the box, it goes through a multi-stage filter to snub out
> RF and some lower-frequency noise (a monolithic cap directly
> across the power socket pins, several turns of wire wrapped through
> a ferrite toroid, and a big 'lytic).  Power for the VE2ZAZ board
> and the GPS/serial-port "schmoo" adapter board then goes through
> a 7809 preregulator and is fed out to these boards.  The filtered
> +16 supply is also fed to an oscillator interface board, which has
> the two 7812 regulators for the oscillator and oven, and the
> DAC-control-voltage coarse-adjust/padding circuity and 7805
> voltage regulator/reference.
>
> The telco board I salvaged the oscillator from, seemed to use
> a somewhat similar approach - it took in +24 VDC from a power
> bus (which I strongly suspect was switcher-regulated) and
> used 7812/7815 regulators to power the oscillator and oven.
>
> The 78xx regulators seem to have pretty good supply-side
> rejection, and so should be attenuating whatever residual
> hash is present on the switcher-generated "raw" DC power
> fairly well.
>
>
>
>