Hi,
I think you meant to say that the B-mode is anywhere between +6 dB or -6
dB from the C-mode.
Anyway, adjusting the 8,8 MHz and 10,7 MHz chains should help. Maybe put
a 47 nF in replacement of C5 of 100 nF? Possibly lower the "high" (which
will become low after the above mod) mode-suppressor somewhat.
Cheers,
Magnus
On 03/12/2016 07:27 PM, Bob Camp wrote:
Hi
The “suppression” of the B mode is variable. Depending on the exact rotation
and contour and plating on the blank, it can be anywhere from 6 db above the
desired B mode to 6 db below. Early crystals ran in the “above” range. As the
world got better at working out the variables, crystals generally run in the
“below” range today.
Early on, putting an oscillator on the C mode was indeed as simple as dropping
it into a standard AT cut third overtone circuit (you still need the
fundamental trap). Up came the unit on the “thermometer” B mode. It was simple
enough and (at the time) obvious enough .. no need to comment on how to do it.
With a modern crystal, randomly chosen from a lot, getting onto the B mode is
fairly tough. You need to reverse the selectivity of the trap. The trap (or
something like it) is still in there to keep the few percent of crystals that
need it happy. The issue being that when something “goes off” a whole batch
need the trap. That’s a big hole in the production schedule.
Bob
On Mar 12, 2016, at 11:24 AM, Richard (Rick) Karlquist <rich...@karlquist.com>
wrote:
Does anyone have a documented way to do this?
I asked the original designers of the 10811
(Burgoon and Wilson) about this a few years
ago and they couldn't remember what the circuit
mods were. I got hold of their lab notebooks
and it wasn't in there either. What I remember
them telling me 35 years ago was that you
remove the complicated mode suppressor between
the base and the emitter and replace it with
the equivalent capacitor. I tried this, and
guess what: it still oscillated in mode C!
All these years no one knew the mode suppressor
wasn't necessary. I tried to redesign the
mode suppressor to suppress mode C. There
wasn't any good way to make this work. I
finally had to finagle the tuned circuit
in the collector to force it to mode B.
My E1938A circuit does not use a mode suppressor
as such. The natural selectivity of the
tank circuit is sufficient.
Can anyone add anything?
Rick
On 3/12/2016 5:33 AM, Magnus Danielson wrote:
Hi,
For the 10811 you can modify it to change mode and then use that mode to
measure and trim the temperature oven.
There exists crystal oscillators where the 10 MHz is a traditional
SC-cut mode and then a 30 MHz mode is exercised which measures the
crystal temperature. In the Microprocessor Controlled Crystal Oscillator
(MCXO) one then measure the difference in frequency and uses this to
re-synthesize a correction on the 10 MHz. The benefit is that it is the
temperature of the oscillating crystal that is being measured.
Naturally, it could be used for oven control and/or EFC control too.
The MCXOs exists in manufacturing, but whenever you ask about them they
just wonder what military project are you working on.
I'd love to experiment with this form of temperature sensing one day,
when I have time... if that ever happens...
Cheers,
Magnus
On 03/12/2016 10:21 AM, ken hartman wrote:
Interestingly, the use of AC-cut crystals (high linear tempco of
frequency)
is found in the development of OCXOs. Using a reference AC-cut
resonator -
in place of the final AT/SC resonator - one can learn much about the
thermal characteristics of the oven loop performance. While not a
precise
temp sensor, it is a high sensitivity indicator of temperature
variations
of the resonator.
On Fri, Mar 11, 2016 at 11:44 PM, Bill Hawkins <bill.i...@pobox.com>
wrote:
It may be that the need for that kind of resolution died out.
The next step up from quartz thermometry is resistance thermometry.
The linearization equation for platinum has enough terms to make it
uncertain around .01 C.
Temperature calibration baths usually use platinum resistance sensors.
It may be that the triple point of water does not have the certainty to
reach '0.0001C'
Disclaimer: I only worked with industrial sensors from Rosemount, Inc.
as an employee.
Bill Hawkins
-----Original Message-----
From: Alan Ambrose
Sent: Friday, March 11, 2016 11:42 AM
Hi,
I hope this is still relevant and not too off-topic...but since it
involves crystals and tempco...
Quartz thermometers (e.g. the HP 2804A) with their 'linear cut' crystals
and '0.0001C resolution' seem to have been a thing from the mid-60's to
the mid-80's:
http://www.hparchive.com/Journals/HPJ-1965-03.pdf
There still appear to be some manufacturers making the crystals:
http://www.statek.com/products/pdf/Temp%20Sensor%2010162%20Rev%20B.pdf
Anyone know why they died out? Did a better technology replace them?
TIA, Alan
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