is there a "best bet" advanced hobbyist buildable GPSDO design?
On Dec 13, 2007 12:00 PM, Scott Burris slburris@gmail.com wrote:
Continuing the design discussions, anyone have opinions about powering
the HP 10811 oscillator?
I'm thinking that you want voltage regulators that are pretty quiet so
as to minimize jitter introduced
via the power supply. To that end, I'm looking at a LT1761 for the +12v
OSC voltage and an LT3080
for the 24v heater supply..
You might try ebay for a +24 / +12 volt switching supply, problem/s solved.
I have bought them for as little as 3 bucks.
Phil
Bruce Griffiths wrote:
Data delay devices (http://www.datadelay.com) also do programmable delay
lines their minimum order is $US75 which isnt too bad particularly if
more than one sawtooth corrector is to be built.
They even do ECL programmable delays as do Micrel (http://www.micrel.com).
However these ECL programmable delay devices dont have enough range for
this application.
There is also a good programmable delay line from Dallas/MAXIM that is
less expensive (see http://www.maxim-ic.com/appnotes.cfm/an_pk/107).
Rick Hambly uses the DS1020-015 in his CNS Clock (see
http://www.cnssys.com). See slides 20, 26, 29 & 30 at
http://gpstime.com/files/tow-time2007.ppt for some details.
One comment on the Dallas/MAXIM DS1020 parts: we (Rick & I) found that
Motorola (in the M12 GPS receiver) and Dallas (in the delay line chip)
have a slightly different (~10%) definition for the nanosecond; it
appears to us that the Dallas/MAXIM definition is wrong, and the same
error shows up in many samples. Rick now uses the 150 psec/step Dallas
chip after finding that the ½ & 1 nsec versions had a scale error (see
slides 16-18 in ftp://ftp.cnssys.com/pub/PTTI/PTTI_2006.ppt which
represents slightly earlier work than presented at the 2007 TOW). The
"true" scale factor with the ~10% correction is contained in a look-up
table that converts the M12M binary sawtooth error output into the value
sent to the delay line.
Season's Greetings to all -- Tom
phil wrote:
On Dec 13, 2007 12:00 PM, Scott Burris slburris@gmail.com wrote:
Continuing the design discussions, anyone have opinions about powering
the HP 10811 oscillator?
I'm thinking that you want voltage regulators that are pretty quiet so
as to minimize jitter introduced
via the power supply. To that end, I'm looking at a LT1761 for the +12v
OSC voltage and an LT3080
for the 24v heater supply..
You might try ebay for a +24 / +12 volt switching supply, problem/s solved.
I have bought them for as little as 3 bucks.
Phil
Can you get switching power supplies with really low noise
characteristics? The LT3080
is rated for 40uV of noise, and the LT1761 is rated for 20uV. The 10811
manual
suggests less than 100uV of noise for the oscillator supply and less
than 30mV for the
heater.
I'm not saying you couldn't get down into the uV range with switchers
with some aggressive
filtering of some sort, but I'm not sure why one would go that route
over a linear supply,
which can hit those numbers with the right regulators. Here I'm valuing
noise characteristics
over efficiency and size.
Scott
Scott
Scott Burris wrote:
Continuing the design discussions, anyone have opinions about powering
the HP 10811 oscillator?
I'm thinking that you want voltage regulators that are pretty quiet so
as to minimize jitter introduced
via the power supply. To that end, I'm looking at a LT1761 for the +12v
OSC voltage and an LT3080
for the 24v heater supply.
How does the output noise of an LT1761 compare with the 5uV rms (100Hz
to 10KHz) output noise of the recommended LM723 regulator?
In reading the 10811 manual, the heater and oscillator are isolated, yet
the example power supply ties
both together in a common ground. That certainly would make things
simpler, as a 24VCT transformer
could be used, and +12 and +24 volts could be made pretty naturally that
way.
The important thing is to regulate the oscillator supply at the
oscillator supply pins and the oven supply at the oven supply pins.
With judicious application of Kelvin sensing the oven and oscillator
supply grounds can be connected together (or heater GND = -12V, Heater
supply = +12V) without significant interaction between the oven current
variations and the oscillator supply voltage. Similarly use Kelvin
sensing techniques (just use a conventional difference amplifier) to
control the EFC voltage between the EFC input and the common oscillator
EFC ground point within the OCXO.
How important in a GPSDO application is it to keep these two sections
completely isolated? I figure I would
either have to use a small HF transformer with a chopper circuit or a
separate 60hz transformer for the second
voltage.
Don't add noise unnecessarily unless you can live with the resultant
OCXO sidebands (or the cost/complexity of a suitable filter to remove
high frequency noise from the power supply).
Scott
Bruce
For low noise Zetex has a nice roll your own option, AN51
Steve
Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
Scott
Scott Burris wrote:
Continuing the design discussions, anyone have opinions about powering
the HP 10811 oscillator?
I'm thinking that you want voltage regulators that are pretty quiet so
as to minimize jitter introduced
via the power supply. To that end, I'm looking at a LT1761 for the +12v
OSC voltage and an LT3080
for the 24v heater supply.
How does the output noise of an LT1761 compare with the 5uV rms (100Hz
to 10KHz) output noise of the recommended LM723 regulator?
In reading the 10811 manual, the heater and oscillator are isolated, yet
the example power supply ties
both together in a common ground. That certainly would make things
simpler, as a 24VCT transformer
could be used, and +12 and +24 volts could be made pretty naturally that
way.
The important thing is to regulate the oscillator supply at the
oscillator supply pins and the oven supply at the oven supply pins.
With judicious application of Kelvin sensing the oven and oscillator
supply grounds can be connected together (or heater GND = -12V, Heater
supply = +12V) without significant interaction between the oven current
variations and the oscillator supply voltage. Similarly use Kelvin
sensing techniques (just use a conventional difference amplifier) to
control the EFC voltage between the EFC input and the common oscillator
EFC ground point within the OCXO.
How important in a GPSDO application is it to keep these two sections
completely isolated? I figure I would
either have to use a small HF transformer with a chopper circuit or a
separate 60hz transformer for the second
voltage.
Don't add noise unnecessarily unless you can live with the resultant
OCXO sidebands (or the cost/complexity of a suitable filter to remove
high frequency noise from the power supply).
Scott
Bruce
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steve heidmann wrote:
For low noise Zetex has a nice roll your own option, AN51
Steve
Steve
They "stole" that circuit topology from the Super regulator circuits
developed by Walt Jung among others.
One of the better sites with info on such regulators is:
http://sjostromaudio.com/joomla/index.php?option=com_content&task=view&id=26&Itemid=27
http://sjostromaudio.com/joomla/index.php?option=com_content&task=view&id=26&Itemid=27
He appears to have a good idea of what he's doing unlike most of the
fanatics in the audio community.
Bruce
On Fri, 14 Dec 2007, Bruce Griffiths wrote:
One of the better sites with info on such regulators is:
http://sjostromaudio.com/joomla/index.php?option=com_content&task=view&id=26&Itemid=27
http://sjostromaudio.com/joomla/index.php?option=com_content&task=view&id=26&Itemid=27
-
This is an unnecessarily complex design. You can achieve the same performance
by cascading the "normal" regular with an integrated low noise regulator. I
prefer Linear Technology ICs for this. -
Bruce and others, you should really check your links before posting them. On
this page was a link to get the full PDF of the schematic. When you click on
that, you get a 404 not found plus you get a popup ad. Worse still, if you
click on the schematic to "enlarge" it, instead of getting the schematic
you get a full page PORN ad.
73,
Jeffrey Pawlan WA6KBL
Pawlan Communications
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Content preview: On Fri, 14 Dec 2007, Bruce Griffiths wrote: > > One of the
better sites with info on such regulators is: > > http://sjostromaudio.com/joomla/index.php?option=com_content&task=view&id=26&Itemid=27
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On Dec 13, 2007 6:24 PM, Bruce Griffiths bruce.griffiths@xtra.co.nz wrote:
They "stole" that circuit topology from the Super regulator circuits
developed by Walt Jung among others.
Bruce can post all the porn links he wants. I'm already going to have to
install a new hard drive to archive all the useful schematics and design
notes he's been contributing! Might as well fill up the remaining space
with SOMETHING.
In case the message isn't clear enough, I really appreciate these pointers,
especially low-noise supply ideas. It's surprising how few off-the-shelf
regulator ICs these days are even as good as the old uA723 from the 1970s.
-- john, KE5FX
-
This is an unnecessarily complex design. You can achieve the
same performance
by cascading the "normal" regular with an integrated low noise
regulator. I
prefer Linear Technology ICs for this. -
Bruce and others, you should really check your links before
posting them. On
this page was a link to get the full PDF of the schematic. When
you click on
that, you get a 404 not found plus you get a popup ad. Worse
still, if you
click on the schematic to "enlarge" it, instead of getting the schematic
you get a full page PORN ad.
John Miles wrote:
Bruce can post all the porn links he wants. I'm already going to have to
install a new hard drive to archive all the useful schematics and design
notes he's been contributing! Might as well fill up the remaining space
with SOMETHING.
In case the message isn't clear enough, I really appreciate these pointers,
especially low-noise supply ideas. It's surprising how few off-the-shelf
regulator ICs these days are even as good as the old uA723 from the 1970s.
-- john, KE5FX
- This is an unnecessarily complex design. You can achieve the
same performance
by cascading the "normal" regular with an integrated low noise
regulator. I
prefer Linear Technology ICs for this.
Actually you cant, which is the point.
- Bruce and others, you should really check your links before
posting them. On
this page was a link to get the full PDF of the schematic. When
you click on
that, you get a 404 not found plus you get a popup ad. Worse
still, if you
click on the schematic to "enlarge" it, instead of getting the schematic
you get a full page PORN ad.
I usually do check the links, the extraneous link to a porn site is
relatively recent "feature" as it wasn't there a few days ago.
I've even seen such transient links appear on the Oscilloquartz site.
For some reason this problem appears to be more prevalent with European
sites, however this may be an indavertent selection effect.
Bruce