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Dear All,<br>
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<p class="MsoNormal">As promised, I would inform you about the working
principle
of Demeter (as it is proposed now!)</p>
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<p class="MsoNormal">It is based on two thoughts:</p>
<ol style="margin-top: 0cm;" start="1" type="1">
<li class="MsoNormal" style="">A switching power supply is more
energy efficient compared to a lineair power supply.</li>
<li class="MsoNormal" style="">A linear power supply provides a
cleaner voltage and a nicer current limit behaviour (something which is
important when things go wrong during experiments).</li>
</ol>
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<p class="MsoNormal">The configuration consists of a switching
pre-regulator and
a linear post-regulator. This combines the best of two different types
of
regulators.</p>
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<p class="MsoNormal">The Demeter proposal as it is now is based on
almost all the
wishes. E.g. it is possible to power the HPSDR through Demeter from the
mains,
the shack power supply and a battery (mobile/emergency operation). On
the other
hand, the implementation will be quite flexible. E.g. people who don’t
need the
battery option can leave out the charger. People who will not use the
mains
supply can reject the transformers, rectifiers and some other
components.</p>
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<p class="MsoNormal">Working principle:</p>
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<p class="MsoNormal">The “Heart”of Demeter is based on a switching
converter
(step-up) with number 10. (The numbers refer to the schematic on: <a
href="http://hpsdr.org/wiki/index.php?title=DEMETER">http://hpsdr.org/wiki/index.php?title=DEMETER</a>)
What it does: It boosts the voltage of an external power supply or the
battery
to a level which is high enough to ensure proper operation of the
12Volt linear
regulator. The output of this step-up converter is used as well as
input for
the 5Volt step down converter and the –12V inverter. (The mentioned
DC-DC
converters have no isolation function!).</p>
<p class="MsoNormal">In case the mains power is used: This voltage will
be the
proper level for the linear regulator. So the DC-DC converter (#10)
will be put
in a power feed-through state.</p>
<p class="MsoNormal">During mains-supply use a negative voltage is
derived from
the transformer at the same time, so DC-DC converter (#17) will be in
feed-through state as well. The only switcher active will be the 5Volt
converter #14.</p>
<p class="MsoNormal">Blocks #3, 9 and 18 are used as “switches”to
choose the
“best”available voltage. Probably the implementation will just consist
of a
Schottky-diode.</p>
<p class="MsoNormal">Each output will be protected with a crow-bar
circuit. This
will probably be a crow-bar using transistors instead of thyristors
(sturdy
thyristors are difficult to get in SMD-housings).</p>
<p class="MsoNormal">The mains supply part consists of two transformers:</p>
<ol style="margin-top: 0cm;" start="1" type="1">
<li class="MsoNormal" style="">Small transformer used for a
“standby-voltage”. The GPS and the OCXO will be powered. To allow
software power-up the USB-hub and the PIC will be powered as well.</li>
<li class="MsoNormal" style="">The main transformer will be switched
on by means of an (electronic) relay. </li>
</ol>
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<p class="MsoNormal">N.B. The main transformer will be a single
secondary winding
transformer.</p>
<p class="MsoNormal">N.B.2 The transformers will be normal
transformers.
Allthough a switcher could be build by amateurs there is a high risk of
an
electric shock or worse. Furthermore, a conventional transformer is
more
tolerant to input supply changes (like a brown-out).</p>
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<p class="MsoNormal">Control and monitoring of the power-supply is done
by a PIC.
Through a multiplexer and a single DAC it will read the various voltage
and
currents. This will be helpful for (remote) monitoring and
trouble-shooting the
power supply. Furtermore, the PIC will be controlling certain parts of
the
power supply (e.g. switching the DC-DC converters in a pass-through
state when
necessary). This will be based on the raw voltage inputs which are
measured as
well.</p>
<p class="MsoNormal">The PIC can act as a frequency reference of the
switchers as
well. This will concentrate the “noise” at a defined frequency, which
can be
electronically adjusted as well. This might be convenient when “noise”
is
within the frequency band of interest.</p>
<p class="MsoNormal">The FAN will be controlled from the PIC as well.
This allows
a more intelligent control of the fan. E.g.<span style="">
</span>a delayed switching off after using the radio and a variable
speed
control.</p>
<p class="MsoNormal">Another suggestion was to add a display read-out
on Demeter
as well. This will make Demeter and the rest of the HPSDR less
dependant on a
PC. E.g. when used with Sasquatch.</p>
<p class="MsoNormal">The USB-hub is incorporated because Demeter will
consume a
USB port. Probably ;-) extra USB-ports will be necessary to control the
HPSDR
and some other periphery. </p>
<p class="MsoNormal">The hub will be arranged in such a way that it has
a
PC-input which will be distributed to four ports. One port will stay
internal
for Demeter, the other three will be available for external use.
Standard IC’s
are available for building an USB-hub so implementation will be quite
easy.</p>
<p class="MsoNormal">As an extra a V++ is available for powering some
power-amplifiers or other circuitry which needs a (slightly) higher
voltage
which might be a bit noisy.</p>
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<p class="MsoNormal">For those who are scared by the switchers in the
deisgn: By
using a proper lay-out and filtering on the right places it must be
possible to
make the power-supply noise-free enough for HPSDR use. Maybe whe need a
Pandora-II…. A Pandora-II will keep out the heat and some noise of the
HPSDR.</p>
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<span style="font-size: 12pt; font-family: "Times New Roman";">From
Henry Vredegoor I/we received an extensive E-mail
with some nice suggestions which I will be looking into.<br>
<br>
73, have a nice weekend, Jeroen PE1RGE<br>
</span>
<pre class="moz-signature" cols="72">--
Ing. Jeroen Bastemeijer
Delft University of Technology
Department of Electrical Engineering
Electronic Instrumentation Laboratory
Mekelweg 4, Room 13.090
2628 CD Delft
The Netherlands
Phone: +31.15.27.86542
Fax: +31.15.27.85755
E-mail: <a class="moz-txt-link-abbreviated" href="mailto:J.Bastemeijer@TUDelft.nl">J.Bastemeijer@TUDelft.nl</a>
GPS: Lat N52.00002 Lon E4.37157 Alt 46.2m</pre>
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