On Freitag, 18. Februar 2022 22:52:27 CET Attila Kinali wrote:
> Quick side note: On modern, cheap TCXO systems, expecially those
> for RTCs, frequency control is being done by a bank of switched
> capacitors. This is mostly because capacitors can be implemented
> in a standard digital CMOS
At that time the synth was set to one frequency and the code went into
sleep , so any buffering resistors etc would have served no purpose.
The TCXO really was hopping over four frequencies in a PN way at intervals
of a little under one second per hop.
Andy
www.g4jnt.com
On Sat, 19 Feb 2022 at
Erik,
What you describe is a classic problem. Especially oven controlled
oscillators will have GND and VCC issues.
I recommend you to look att both frequency and phase deviation plots.
Systematics like these is mangled up in a ADEV plot.
Regardless of what isuse you really had, I hope you
Andy, do you have the PIC and the synthesiser chip data control lines
well buffered/isolated (nice big resistors etc on the data lines ?)
Any sort of current you inject into the synth chip will find its way
onto the output
On 19/02/2022 7:55 pm, Andy Talbot wrote:
A while back I
Magnus, others
My previous mail was not very clear but the jumping problem was solved.
It was not caused by the TCXO but by small current fluctuations in the TCXO
causing small VCC fluctuations causing feedback into he Vtune input because
the Vtune was derived from the VCC.
I just did not realize
Erik,
So, your pick of VC-TCXO is one that obviously seems to use the
fractional synthesis to both set the output frequency as well as
compensate for temperature. The modulations you have will be intrinsic
to the pick.
As you lock your VC-TCXO to a GPS, the average frequency will be locked
Hi
Sounds like you might want to try a different TCXO. Or even
try an OCXO. Even with a good TCXO, 1x10^-9 accuracy is
a stretch. I’m assuming we’re talking frequency accuracy so
the usual “one sigma” time accuracy not the overriding number.
GPS module “output jitter” forces you to a fairly
A while back I purchased a low cost TCXO which I then used as the reference
for a synthesizer generating 10GHz. Listening to the output on an SSB
radio, the tone was hopping in a random fashion over four frequencies,
spaced a few tens of Hz apart. This was surreal! I had, at that time,
been
Thanks for all the excellent info
The TCXO is actually a VC-TCXO at 10MHz intended for use in a cheap
GPSDO where the ambition is to have 1e-9 frequency accuracy so the 2e-9
jump was just too high.
The VC-TCXO had its own low noise voltage regulator but the Vtune was
connected to a variable
I have used the switched capacitor type, with direct control over the
switching caps .
We were able to high speed dither the switch settings to get 1/2 and 1/4
and 1/8 steps of the minimum capacitor switch step. This way, we got
high control resolution.
BUT- this only works for requirements
Hi Erik,
I only saw that thread later, and I will have to return to that as I
have a little more energy.
I'm trying to get you up to speed with the many variants there is, and
there is plenty experience here to feed from. What may be true for one
device will not make any sense for another.
On Fri, 18 Feb 2022 11:56:02 +0100
Magnus Danielson via time-nuts wrote:
> I think you have yourself a digital TCXO controller. Those use a
> tempsensor, use the reading to calculate the compensation and the use a
> normal varactor control to steer the frequency.
Quick side note: On modern,
Hi
If it’s a sub $1 device, it’s pretty much guaranteed that it has digital
“stuff” inside it. That circuitry will generate blips and pops totally
independent of any attempt it makes at compensation. If it “wakes
up” this or that digital sub section every 107.34 seconds, you get
an internal
Hi Magnus,
Tom also replied to my question and suggested a 107.34 seconds interval
related to dithering with a 1e7/2^30 interval
Unfortunately the datasheet is rather short (sub $1 device) and does not
provide any hints to being a digital implementation.
Thanks to all for helping!
Erik.
Bill,
To test I removed the thermal insulation to increase the heat loss
requiring more heat to be generated.
The jump pattern did not change!
Erik.
On 18-2-2022 11:26, bill wrote:
Hello,
My guess is that it is a quirk of the temperature compensation network
inside the TCXO. I have seen
Hi Erik,
I think you have yourself a digital TCXO controller. Those use a
tempsensor, use the reading to calculate the compensation and the use a
normal varactor control to steer the frequency. Older TCXOs use a
resistor/thermistor network to do the same work. You can probably read
up on the
Mike, the counter resolution was 40ps with am RMS resolution of 120ps
Erik.
On 18-2-2022 11:36, Mike Ingle wrote:
Hi Erik.
What is your counter resolution/gate time? At 1second, the interval
difference from 10MHz + 5mHz is 500ps. --mike
On Fri, Feb 18, 2022 at 11:20 AM Erik Kaashoek wrote:
Hi Erik.
What is your counter resolution/gate time? At 1second, the interval
difference from 10MHz + 5mHz is 500ps. --mike
On Fri, Feb 18, 2022 at 11:20 AM Erik Kaashoek wrote:
> During long term testing of some 10 MHz TCXO the output frequency seems
> to jump within one second 20 mHz (
Hello,
My guess is that it is a quirk of the temperature compensation network
inside the TCXO. I have seen similar behavior in commercial TCXOs as
temperature changes as a result of "break points" in the compensation
network. It is difficult to know exactly unless it is possible to
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