Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages and
the disadvantages and which the extension of spectral harmonicas.
In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Anticipated thanks.

73's de IK6GQC Rocco

From: Mario Bros on Jul 17, 4:34 pm

Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages and
the disadvantages and which the extension of spectral harmonicas.

The TTL and HCMOS outputs will have (generally) square waves
which are rich in odd harmonic content. Clipped sine waves
have less overall harmonics...but the harmonic content depends
on the amount of clipping (presumably off the peak of the sine).


In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Depends entirely on the designer's choice. If this is a
purchased TCXO unit then a clipped sinewave output would
probably come through a buffer stage directly from the
internal oscillator output...which resembles a clipped
sine wave. For the purchased unit, having that output is
a convenience to the customer.

TTL and HCMOS outputs would be made from internal digital
devices, again a customer convenience to allow easy interface
to external TTL or HCMOS circuitry.

bit bit

The clipped sinewave is the simplest output for a TCXO, it's usually just a
capacitor connected between the emitter of the oscillator and the output pin.
You have to be careful what you connect to it, it's possible to throw the temp
compensation out of tolerance. Most CMOS PLL chips have a reference frequency
input that handles it well. If you're rolling your own PLL from SSI or MSI
chips, you probable want to build up a buffer to make the clipped sinewave into
TTL or HCMOS levels, or pay extra for a TCXO with the needed circuit built in.




On Sun, 17 Jul 2005 20:34:25 GMT, "Mario Bros" wrote:

Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages and
the disadvantages and which the extension of spectral harmonicas.
In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Anticipated thanks.

73's de IK6GQC Rocco

Thanks for the answers.
I have one TCXO 40Mhz 1Vp-p 10K//15pf Clipped Sine Wave.
My idea is of:
1) to gain 40Mhz Sine Wave through buffer with resonant circuit come
to an agreement for 2nd the IF (40.455)
2) to gain 20Mhz with a divisor x2 for the 16F877
3) ..and last.. to gain before 120Mhz (40x3) and then 480Mhz with
helical filter for clock the AD9954.
Thoughts are possible? It is one bad solutions??
Thank you again.



ha scritto nel messaggio
...
The clipped sinewave is the simplest output for a TCXO, it's usually just
a
capacitor connected between the emitter of the oscillator and the output
pin.
You have to be careful what you connect to it, it's possible to throw the
temp
compensation out of tolerance. Most CMOS PLL chips have a reference
frequency
input that handles it well. If you're rolling your own PLL from SSI or MSI
chips, you probable want to build up a buffer to make the clipped sinewave
into
TTL or HCMOS levels, or pay extra for a TCXO with the needed circuit built
in.




On Sun, 17 Jul 2005 20:34:25 GMT, "Mario Bros" wrote:

Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages
and
the disadvantages and which the extension of spectral harmonicas.
In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Anticipated thanks.

73's de IK6GQC Rocco

It all sounds possible to me. It is not very different from some of
the schemes we use commercially to generate internal frequencies (in
spectral analysis equipment). Your idea of good filtering at 480MHz
(and also, I hope, at 120MHz) is a good one, to keep out other
combinations of multiplication. The one other thing I would be careful
about is the phase noise of the oscillator. The AD9954 should be
capable of very good phase noise performance, but you MUST feed it a
clean reference to keep the output clean. I have recently tested some
TCXOs which are very stable and accurate, but whose phase noise is not
as good as I would really like. It is important to feed the oscillator
from a very clean supply, but that alone is not a guarantee of good
phase noise. See http://www.techlib.com/electronics/finesse.html for a
nice idea to make a very clean supply for circuits that draw
essentially constant current.

Cheers,
Tom

Hi Tom,
Thanks for the councils. An alternative could be an oscillator (480 Mhz)
with 1/4 coax resonator and IC
PLL TSA5511 I2C Bus clocked by 40Mhz/10 (4mhz)...
I must think to us...

Ciao IK6GQC Rocco

"K7ITM" ha scritto nel messaggio
oups.com...
It all sounds possible to me. It is not very different from some of
the schemes we use commercially to generate internal frequencies (in
spectral analysis equipment). Your idea of good filtering at 480MHz
(and also, I hope, at 120MHz) is a good one, to keep out other
combinations of multiplication. The one other thing I would be careful
about is the phase noise of the oscillator. The AD9954 should be
capable of very good phase noise performance, but you MUST feed it a
clean reference to keep the output clean. I have recently tested some
TCXOs which are very stable and accurate, but whose phase noise is not
as good as I would really like. It is important to feed the oscillator
from a very clean supply, but that alone is not a guarantee of good
phase noise. See http://www.techlib.com/electronics/finesse.html for a
nice idea to make a very clean supply for circuits that draw
essentially constant current.

Cheers,
Tom

Hi Rocco,

I would use the multiplication. Within the loop bandwidth of the PLL,
the phase noise will be determined by the crystal oscillator used as a
reference PLUS the noise contributed by the PLL chip itself (the phase
comparator and loop filter/amplifier), and outside the loop bandwidth,
it will be determined by the VCO used in the PLL. The important
thing, whether you use a PLL or multiplication, is to start with a
reference which has low phase noise. In fact, your TCXO may have good
phase noise...I don't know...I only know that some I've tested have not
been as clean as I'd like. But I'm also setting pretty high standards
for what I'm doing.

If I were in your shoes, I would build the multiplier system just as
you first described, and use the TCXO you have, and if it proves to be
too noisy (phase noise), then look for a better oscillator. If you can
make even a crude measurement of the oscillator's phase noise before
you start, that would be good, too, just to know where you are
starting. My comment in my earlier posting was just to make you aware
to look at phase noise, not to change the basic way you are going about
it.

Cheers,
Tom

In message , Mario Bros
writes
Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages and
the disadvantages and which the extension of spectral harmonicas.
In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Anticipated thanks.

73's de IK6GQC Rocco


I designed some of the first TCXOs , simple oscillators manufactured
they used no agc control and relied on the average oscillator
maintaining circuit gain to drop to limit oscillation level. Hence
clipped sine.
I.E gain during the transition and no gain during limiting.
This output then coupled to a buffer amp for isolation was the
Lowest cost option.
When logic compatibility was required a logic buffer or open collector
provided.
Also I note that (many years ago) when the first prototypes were
required I looked through a junk box for any small case and selected
most appropriate arbitary case.
These TCXO OCXO case dimensions can now be found as standard from many
TCXO / OCXO manufacturers around the world.
--
dd

In message , Mario Bros
writes
Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages and
the disadvantages and which the extension of spectral harmonicas.
In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Anticipated thanks.

73's de IK6GQC Rocco


A further note the ssb noise will depend on the crystal Q the noise
level in the compensation circuit and the level of crystal oscillation.
Best with no compensation circuit ie XO or OCXO
The smallest crystals cannot be driven as hard as the bigger ones so
dont go for the smallest case!
The easiest way to indicate ssb noise may be to beat two identical
oscillators together with a few HZ offset.
Or lock one to the other using the voltage control line (exclusive or is
the easiest PLL circuit?)
The display the lock voltage on a scope.


--
dd

Hi Doug,
A lot interesting. Thanks for the ulterior contribution.
In these days I will make some test in order to try the better
solution.

73's de IK6GQC Rocco

"doug dwyer" ha scritto nel messaggio
...
In message , Mario Bros
writes
Hi folks,
I would have to ask a clarification regard to the TCXO.
They are found with output TTL, HCMOS and CLIPPED SINE WAVE.
It is just with respect to this last type that I would want to have
elucidations on when it is convenient to employ it, which the advantages
and
the disadvantages and which the extension of spectral harmonicas.
In synthesis, from the plan point of view, which are the motivations that
they make to incline towards a Clipped oscillator?

Anticipated thanks.

73's de IK6GQC Rocco


A further note the ssb noise will depend on the crystal Q the noise level
in the compensation circuit and the level of crystal oscillation.
Best with no compensation circuit ie XO or OCXO
The smallest crystals cannot be driven as hard as the bigger ones so dont
go for the smallest case!
The easiest way to indicate ssb noise may be to beat two identical
oscillators together with a few HZ offset.
Or lock one to the other using the voltage control line (exclusive or is
the easiest PLL circuit?)
The display the lock voltage on a scope.


--
dd