On Oct 30, 11:30�am, m...@linnix.info-for.us wrote:
> > Reference Oscillator Crystal Requirements for the MC1320x, MC1321x,
>
> > MC1322x, and MC1323x IEEE 802.15.4 Devices
>
> > <http://cache.freescale.com/files/rf_if/doc/app_note/AN3251.pdf>
>
> > (Note that the chips have internal switched capacitors for both coarse
>
> > and fine tuning.) &#4294967295;Basically, they want +/-40ppm over the operating
>
> > temperature range. &#4294967295;That should be possible without any elaborate
>
> > external TCXO style temperature compensation. &#4294967295;Just buy a decent AT
>
> > cut series resonant crystal, with a low series resistance, and keep
>
> > the board clean.
>
> I was luck to have the first prototype working with this crystal:
> 50ppm stability and 20ppm tolerance
>
> http://www.digikey.com/product-detail/en/445C25D20M00000/CTX1164CT-ND...
>
> However, board #2 and #3 does not work with cheaper crystal:
> 20ppm as they claim.
>
> I'll spend a little more crystals and probably get the 10ppm, when i am ready to order more parts.
>
> Yes, the Freescale MC13202's cap trimming would be helpful in temp. compensation, which could be a problem later on.

Followup on this:
All my MRF24J40s are working now, with the CTX SMD ceramic crystal.

           ICAP|ECAP|ESR| STAB|TOL
CTX1164   |18pf|18pf| 40|50PPM|20PPM		// OK
CTX1172   |18pf|18pf| 40|30PPM|20PPM		// OK
445C33L20M|12pf|18pf| 40|30PPM|20PPM		// Out of stock, will try
445C22L20M|12pf|18pf| 40|20PPM|20PPM		// 1K min, wlll try

BTW, the MC13202 spec for
           ICAP|ECAP|ESR| STAB|TOL
            9pf|18pf| 40|10PPM|10PPM		// Custom order?


However, nothing in the spec of the non-working HC-59S would indicate
why it won't work.

 
> Reference Oscillator Crystal Requirements for the MC1320x, MC1321x,
> 
> MC1322x, and MC1323x IEEE 802.15.4 Devices
> 
> <http://cache.freescale.com/files/rf_if/doc/app_note/AN3251.pdf>
> 
> (Note that the chips have internal switched capacitors for both coarse
> 
> and fine tuning.)  Basically, they want +/-40ppm over the operating
> 
> temperature range.  That should be possible without any elaborate
> 
> external TCXO style temperature compensation.  Just buy a decent AT
> 
> cut series resonant crystal, with a low series resistance, and keep
> 
> the board clean. 

I was luck to have the first prototype working with this crystal:
50ppm stability and 20ppm tolerance

http://www.digikey.com/product-detail/en/445C25D20M00000/CTX1164CT-ND/3135104

However, board #2 and #3 does not work with cheaper crystal:
20ppm as they claim.

I'll spend a little more crystals and probably get the 10ppm, when i am ready to order more parts.

Yes, the Freescale MC13202's cap trimming would be helpful in temp. compensation, which could be a problem later on.

On Sat, 27 Oct 2012 22:15:19 -0400, "Martin Riddle"
<martin_rid@verizon.net> wrote:

>Make sure the board is cleaned properly. The No clean flux can cause 
>problems for crystals, especially under the crystal.

True.  In a past life, I designed marine radios.  As one would expect,
marine radios tend to get wet, usually from condensation.  

Ionic contaminants on the PCB are NOT much of a problem, until the
board gets wet.  Then, the stuff really conducts.  One board that I
ran through a worst case test in our then modern wave soldering
machine showed about 20K/square sheet resistivity.  To high impedance
circuits, long parallel traces, and voltage threshold activated
circuits, that's almost like a short circuit.  

The general solution is to design using low impedances wherever
possible.  However, that won't work for crystal oscillators, which are
high impedance devices.  So, you're stuck with keeping the board
clean, or at least the area around the crystal clean.  Once you get it
clean, you might also need some conformal coating.  (Not the entire
board as that makes rework difficult.  Just the areas that are deemed
moisture sensitive).

When we switched from rosin flux to water soluable flux in the 1970's,
we had nothing but problems.  Initially, it was rather stupid
problems, such as using an unfiltered water rinse with far too much
calcium both in the water and sitting in the bottom of the water
heater.  Later, they became more difficult, such as uneven rinsing in
the modified dish washer that was used for washing.  Every board had
several test traces which were used to estimate resistivity.  When we
knew they were baked dry, and all the rinse water was gone, they were
conformal coated, usually with acrylic.  In short, board cleaning
after soldering with water soluable flux was not a trivial exercise.

I've never done anything with Zigbee, so I'm not really familiar with
the frequency stability requirements.  Googling...  This app note goes
into the requirements in detail:
Reference Oscillator Crystal Requirements for the MC1320x, MC1321x,
MC1322x, and MC1323x IEEE 802.15.4 Devices
<http://cache.freescale.com/files/rf_if/doc/app_note/AN3251.pdf>
(Note that the chips have internal switched capacitors for both coarse
and fine tuning.)  Basically, they want +/-40ppm over the operating
temperature range.  That should be possible without any elaborate
external TCXO style temperature compensation.  Just buy a decent AT
cut series resonant crystal, with a low series resistance, and keep
the board clean. 


-- 
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Hello Jon,

not announcing a Followup-To: is bad.

So again for c.a.e:

hundreds of ohms between nets will kill most circuits, anyhow.

If they don't kill them immediately, they will do slowly by
electrochemical migration.

Cleaning boards is not easy. No clean often means "no chance to
clean".

Oliver
-- 
Oliver Betz, Munich (oliverbetz.de)

On Mon, 29 Oct 2012 12:38:52 +0100, Oliver Betz <obetz@despammed.com>
wrote:

>"Martin Riddle" wrote:
>
>[...]
>
>>Make sure the board is cleaned properly. The No clean flux can cause 
>>problems for crystals, especially under the crystal.
>
>could you explain this further, what kind of influence are you talking
>about?
>
>Oliver

I have not been followed this discussion with great attention, but
there are several issues related to PCB material humidity and
temperature dependencies in oscillators.

When building free running HF oscillators (e.g. VFOs) never use two
(or multi) layer constructions near the LC resonant circuit. The stray
capacitance between the resonant LC components and the PCB ground
plane affects the frequency. Unfortunately, this stray capacitance
varies with the air humidity and temperature, which affects the
dielectric constant of the PCB material and hence affect the
frequency.

For simple oscillators in the UHF/microwave range, a free running
oscillator made of 1/4 wavelength PCB traces are extremely sensitive
to these issues. 

Anyway, one should remember that a frequency drift of 1 Hz at 25 MHz
is 100 Hz at 2.45 GHz. I was once debugging a GHz signal source based
on some VHF overtone crystals and wondered, why the frequency was
shifting every few seconds. I finally discovered that I was breathing
on the crystal, that cased the frequency drift :-).

When using HF fundamental or VHF overtone crystals as a reference to
frequency multipliers or PLLs, you really need to pay attention to the
PCB material and layout around the crystal oscillator.

Jamie wrote:

[...]

>>>Make sure the board is cleaned properly. The No clean flux can cause 
>>>problems for crystals, especially under the crystal.
>> 
>> could you explain this further, what kind of influence are you talking
>> about?
>
>  Think about that, the flux gets heated in the process and many fluxes 
>are made with organics that can break down to carbon. Also, years ago, I
>had some flux that I stuck the probes of a cap meter into and I was very
>surprised at the dialectic value it had..

I think the air gap between the case and the board will contribute
much more uncertainty.

Oliver
-- 
Oliver Betz, Munich (oliverbetz.de)

linnix wrote:


> 
> Until i get the 2.5GHz frequency counter, i just have to keep trying
> different crystals and caps.  I wonder if it's because of the ceramic
> SMD vs. metal case HC-59 crystal, in terms of para. caps.

You don't need a 2.5 GHz counter to check the crystal, it is running
at a much lower frequency.  Trying to count the modulated output
of the transceiver will probably be a mess, too.  Also, it is probably
turning on and off for short bursts, which will also interfere with
getting a valid count.  Make a coil about the size of the crystal
and maybe 5-10 turns.  First hook to a scope probe and see if you
can pick up the crystal oscillator.  If it looks real fuzzy, that
may indicate the frequency is unstable, ie. the crystal is not being
resonated at high Q.  You may also see the crystal is running on the 3rd
harmonic, they REALLY like to do this.  Increasing the resonating cap
value usually pulls them back down into the right range.

Generally, the crystal makers specify a resonating cap value, you
double this value if you have a capacitor to ground at each end
of the crystal.  So, if they spec 15 pF, you put a 30 pF cap at
each end of the crystal.

If you can get a visible signal that is remotely within range of what
it is supposed to be, then try the freq. counter to measure it more
accurately.  After changing the caps, power up many times to make
sure it starts reliably every time, and maybe over a range of
temperatures, too.

Jon

Oliver Betz wrote:

> "Martin Riddle" wrote:
> 
> [...]
> 
>>Make sure the board is cleaned properly. The No clean flux can cause
>>problems for crystals, especially under the crystal.
> 
> could you explain this further, what kind of influence are you talking
> about?
This usually doesn't show up right away.  It develops over weeks or months.
Some fluxes, like "no-clean" can be pretty high impedance, especially right
after soldering or reflow.  Then, they absorb water, and the conductivity
goes up.  Many logic inverter-type oscillators need some amount of
conductance between the two crystal terminals to put the inverter input
near the transition.  But, too much conductance and the oscillator
may fail to start, or may hop in frequency.  In some cases I've seen
conductance between adjacent chip pins in the hundreds of Ohms, which
would certainly kill the Q of an oscillator.  Cleaning the boards carefully
with a toothbrush and solvent will fix the problem.  It can sometimes
be hard to get solvent under SMT components, and that's where these
deposits like to hide.

Jon

On Monday, October 29, 2012 4:38:50 AM UTC-7, Oliver Betz wrote:
> "langwadt@fonz.dk" wrote:
> 
> 
> 
> >> > my point is that for each different type of xtal you need to measure
> 
> >> > the resulting frequency and adjust the caps, it can be much more than
> 
> >> > 40ppm
> 
> >> > off
> 
> >>
> 
> >> Until i get the 2.5GHz frequency counter, i just have to keep trying
> 
> >> different crystals and caps. �I wonder if it's because of the ceramic
> 
> >> SMD vs. metal case HC-59 crystal, in terms of para. caps.
> 
> >
> 
> >you can just measure the xtal frequency
> 
> 
> 
> where "just measure" means using a high impedance (low capacitance)
> 
> probe or an output not connected to the crystal.
> 

The MC13202 has a separate Clock out pin, driving the microcontroller.  Together with the cap trimmings, we might be able to have the frequency calibration build-in.  This might make it a winner over the MRF24J40 and AT86RF231.

Oliver Betz wrote:

> "Martin Riddle" wrote:
> 
> [...]
> 
> 
>>Make sure the board is cleaned properly. The No clean flux can cause 
>>problems for crystals, especially under the crystal.
> 
> 
> could you explain this further, what kind of influence are you talking
> about?
> 
> Oliver

  Think about that, the flux gets heated in the process and many fluxes 
are made with organics that can break down to carbon. Also, years ago, I
had some flux that I stuck the probes of a cap meter into and I was very
surprised at the dialectic value it had..

  I am sure there are different formulas for specific applications..

Jamie