Dear Rick,
> When asking questions such as this, it is helpful to know why you need to
> know the part number.
Basically to complete my documentation, but there is more to it...
Please let me start with a nut shell introduction. I'm going to build a GPSDO
and will use the following key building blocks:GPS receiver (Oncore UT+) with
an outdoor antenna for a precise 1PPS.HQ 10MHz oscillator with EFC (initially
the 10811, later switched to the E1938).Dividers (HC390) to come to 1Hz.PLL
(HC7046) to compare 1PPS & 1Hz and tune the oscillator.Power supply, to feed
the animals.
Nothing exiting so far. To check on the outside if the instrument is working
properly, I want to have some checks:Oven error LED, is the oven on temperature
(not too cold, not too hot). LED on = error.1PPS from GPS LED, only flashing
when at least five satellites are contributing.PLL Lock LED, on when 1PPS & 1Hz
are in sync.EFC voltage readout (3½ digit), to monitor excessive drift.
Now about the oven warning LED. The idea is to use the "Thermistor Bridge out"
pin (8) on the 15P 'Puck' D-sub and the "Them. Bridge Reference" (pin 15) for
this.So, I connected with two wires (40mm/1.6" length) both above mentioned
pins with the not used pins 19 & 20 in the special D-sub. Now I can connect the
oscillator board with one cable (20cm/8") to my own PCB and use two comparators
to make a small window for an alarm. The reference I only will use to determine
the 'on temperature voltage'.However, when reading your article "A LOW-PROFILE
HIGH-PERFORMANCE CRYSTAL OSCILLATOR FOR TIMEKEEPING APPLICATIONS" I noticed
that you talk about 'picking up noise due to a long path from reference to the
controller board'. That brought me to the schematics of the reference voltage
and the IC. My doubt now is that my leads will increase the chance on errors in
the delicate control system.Can you please elaborate on that, is there indeed a
risk?
> I do remember that I originally used some convenient reference which seemed
> OK from the data sheet, but turned out to be too noisy. I changed it to a
> different one.
That emphasises my earlier mentioned feeling, but also brings me to a next
questions:I have two different versions of the E1938. One contains two DAC
IC's, the other only one DAC.What is the reason for changing this?Was the noisy
reference IC ever used in production (so, might it be present in the two DAC
version)?Is it possible to publish an older revision of the schematics that
reflects the two DAC version that was produced (and if applicable the
oscillator unit)?
Best regards, Rob.
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