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802.15.4 RF issues
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linnix
Oct 27, 2012, 1:22:23 PM10/27/12
to
We are using the Microchip MRF24JA40 802.15.4 RF transceiver,
might look into Atmel's AT86RF231 and Freescale's MC13202 as well. We
have one working board talking to a Microchip pre-made module, but two
non-working boards. The only difference is the crystal. The working
one is 5 mm SMD and the non-working one is 11 mm 2 pins. Could it be
so sensitive to crystal selection? Do we need to pre-screen them for
productions?
The Freescale chip allows crystal calibration, but won't solve drift
problem. My non-working board detects signals occasionally, but not
good enough to pull in any packet. It seems to be drifting in and out
of the channel.
Also, the 1/4 length for 2.5GHz is 3cm. Most WiFI antenna seems to be
bigger. Are they 3/4 length? Would 1-1/4 be better? We are just
using a wire coiled on top of the PCB.
might look into Atmel's AT86RF231 and Freescale's MC13202 as well. We
have one working board talking to a Microchip pre-made module, but two
non-working boards. The only difference is the crystal. The working
one is 5 mm SMD and the non-working one is 11 mm 2 pins. Could it be
so sensitive to crystal selection? Do we need to pre-screen them for
productions?
The Freescale chip allows crystal calibration, but won't solve drift
problem. My non-working board detects signals occasionally, but not
good enough to pull in any packet. It seems to be drifting in and out
of the channel.
Also, the 1/4 length for 2.5GHz is 3cm. Most WiFI antenna seems to be
bigger. Are they 3/4 length? Would 1-1/4 be better? We are just
using a wire coiled on top of the PCB.
lang...@fonz.dk
Oct 27, 2012, 1:41:11 PM10/27/12
to
On 27 Okt., 19:22, linnix <m...@linnix.info-for.us> wrote:
> We are using the Microchip MRF24JA40 802.15.4 RF transceiver,
> might look into Atmel's AT86RF231 and Freescale's MC13202 as well. We
> have one working board talking to a Microchip pre-made module, but two
> non-working boards. The only difference is the crystal. The working
> one is 5 mm SMD and the non-working one is 11 mm 2 pins. Could it be
> so sensitive to crystal selection? Do we need to pre-screen them for
> productions?
>
a different crystal will probably need different capacitors to be
> We are using the Microchip MRF24JA40 802.15.4 RF transceiver,
> might look into Atmel's AT86RF231 and Freescale's MC13202 as well. We
> have one working board talking to a Microchip pre-made module, but two
> non-working boards. The only difference is the crystal. The working
> one is 5 mm SMD and the non-working one is 11 mm 2 pins. Could it be
> so sensitive to crystal selection? Do we need to pre-screen them for
> productions?
>
spot
on frequency. Try measuring the frequency, 802.15.4 requires
something
like +/-40ppm
> The Freescale chip allows crystal calibration, but won't solve drift
> problem. My non-working board detects signals occasionally, but not
> good enough to pull in any packet. It seems to be drifting in and out
> of the channel.
to
stay with in +/40ppm over temperature and aging
>
> Also, the 1/4 length for 2.5GHz is 3cm. Most WiFI antenna seems to be
> bigger. Are they 3/4 length? Would 1-1/4 be better? We are just
> using a wire coiled on top of the PCB.
what
ever their put on give an acceptable performance
but if devices are close I don't think it matters much
I worked on developing the freescale 802.15.4 stuff but that was many
years ago
-Lasse
linnix
Oct 27, 2012, 1:59:34 PM10/27/12
to
On Oct 27, 10:41 am, "langw...@fonz.dk" <langw...@fonz.dk> wrote:
> On 27 Okt., 19:22, linnix <m...@linnix.info-for.us> wrote:
>
> > We are using the Microchip MRF24JA40 802.15.4 RF transceiver,
> > might look into Atmel's AT86RF231 and Freescale's MC13202 as well. We
> > have one working board talking to a Microchip pre-made module, but two
> > non-working boards. The only difference is the crystal. The working
> > one is 5 mm SMD and the non-working one is 11 mm 2 pins. Could it be
> > so sensitive to crystal selection? Do we need to pre-screen them for
> > productions?
>
> a different crystal will probably need different capacitors to be
> spot
> on frequency. Try measuring the frequency, 802.15.4 requires
> something
> like +/-40ppm
The non-working one says 20ppm, not sure if it's stability or
> On 27 Okt., 19:22, linnix <m...@linnix.info-for.us> wrote:
>
> > We are using the Microchip MRF24JA40 802.15.4 RF transceiver,
> > might look into Atmel's AT86RF231 and Freescale's MC13202 as well. We
> > have one working board talking to a Microchip pre-made module, but two
> > non-working boards. The only difference is the crystal. The working
> > one is 5 mm SMD and the non-working one is 11 mm 2 pins. Could it be
> > so sensitive to crystal selection? Do we need to pre-screen them for
> > productions?
>
> a different crystal will probably need different capacitors to be
> spot
> on frequency. Try measuring the frequency, 802.15.4 requires
> something
> like +/-40ppm
tolerence. However, the cheap stuff (10 for $1.95 including shipping
from Hong Kong) might be fake. The working one (80 cents + $3
shipping from digikey) is actually 30ppm. Will try to order more test
crystals later.
>
> > The Freescale chip allows crystal calibration, but won't solve drift
> > problem. My non-working board detects signals occasionally, but not
> > good enough to pull in any packet. It seems to be drifting in and out
> > of the channel.
>
> I believe if you get the caps right wor the crystal you should able
> to
> stay with in +/40ppm over temperature and aging
>
>
>
> > Also, the 1/4 length for 2.5GHz is 3cm. Most WiFI antenna seems to be
> > bigger. Are they 3/4 length? Would 1-1/4 be better? We are just
> > using a wire coiled on top of the PCB.
>
> all kinds of different antennas as long as it is matched I'd assume
> what
> ever their put on give an acceptable performance
>
> but if devices are close I don't think it matters much
>
> I worked on developing the freescale 802.15.4 stuff but that was many
> years ago
>
> -Lasse
(on the devices) is much weaker than the Microchip module
(coordinator), but seems to be OK.
lang...@fonz.dk
Oct 27, 2012, 2:18:33 PM10/27/12
to
On 27 Okt., 19:59, linnix <m...@linnix.info-for.us> wrote:
> On Oct 27, 10:41 am, "langw...@fonz.dk" <langw...@fonz.dk> wrote:
>
> > On 27 Okt., 19:22, linnix <m...@linnix.info-for.us> wrote:
>
> > > We are using the Microchip MRF24JA40 802.15.4 RF transceiver,
> > > might look into Atmel's AT86RF231 and Freescale's MC13202 as well. We
> > > have one working board talking to a Microchip pre-made module, but two
> > > non-working boards. The only difference is the crystal. The working
> > > one is 5 mm SMD and the non-working one is 11 mm 2 pins. Could it be
> > > so sensitive to crystal selection? Do we need to pre-screen them for
> > > productions?
>
> > a different crystal will probably need different capacitors to be
> > spot
> > on frequency. Try measuring the frequency, 802.15.4 requires
> > something
> > like +/-40ppm
>
> The non-working one says 20ppm, not sure if it's stability or
> tolerence. However, the cheap stuff (10 for $1.95 including shipping
> from Hong Kong) might be fake. The working one (80 cents + $3
> shipping from digikey) is actually 30ppm. Will try to order more test
> crystals later.
>
my point is that for each different type of xtal you need to measure
> On Oct 27, 10:41 am, "langw...@fonz.dk" <langw...@fonz.dk> wrote:
>
> > On 27 Okt., 19:22, linnix <m...@linnix.info-for.us> wrote:
>
> > > We are using the Microchip MRF24JA40 802.15.4 RF transceiver,
> > > might look into Atmel's AT86RF231 and Freescale's MC13202 as well. We
> > > have one working board talking to a Microchip pre-made module, but two
> > > non-working boards. The only difference is the crystal. The working
> > > one is 5 mm SMD and the non-working one is 11 mm 2 pins. Could it be
> > > so sensitive to crystal selection? Do we need to pre-screen them for
> > > productions?
>
> > a different crystal will probably need different capacitors to be
> > spot
> > on frequency. Try measuring the frequency, 802.15.4 requires
> > something
> > like +/-40ppm
>
> The non-working one says 20ppm, not sure if it's stability or
> tolerence. However, the cheap stuff (10 for $1.95 including shipping
> from Hong Kong) might be fake. The working one (80 cents + $3
> shipping from digikey) is actually 30ppm. Will try to order more test
> crystals later.
>
the resulting frequency and adjust the caps, it can be much more than
40ppm
off
>
> > > The Freescale chip allows crystal calibration, but won't solve drift
> > > problem. My non-working board detects signals occasionally, but not
> > > good enough to pull in any packet. It seems to be drifting in and out
> > > of the channel.
>
> > I believe if you get the caps right wor the crystal you should able
> > to
> > stay with in +/40ppm over temperature and aging
>
> > > Also, the 1/4 length for 2.5GHz is 3cm. Most WiFI antenna seems to be
> > > bigger. Are they 3/4 length? Would 1-1/4 be better? We are just
> > > using a wire coiled on top of the PCB.
>
> > all kinds of different antennas as long as it is matched I'd assume
> > what
> > ever their put on give an acceptable performance
>
> > but if devices are close I don't think it matters much
>
> > I worked on developing the freescale 802.15.4 stuff but that was many
> > years ago
>
> > -Lasse
>
> I have a 9cm wire talking to the Microchip's PCB E antenna. My signal
> (on the devices) is much weaker than the Microchip module
> (coordinator), but seems to be OK.
Tim Wescott
Oct 27, 2012, 2:21:29 PM10/27/12
to
ground plane underneath your crystal lands, then you've got capacitors,
and those capacitors' temperature behavior is no better than the PCB
material's.
See if your manufacturer of choice has any app notes on layout for good
oscillator stability.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
linnix
Oct 27, 2012, 2:26:52 PM10/27/12
to
>
> See if your manufacturer of choice has any app notes on layout for good
> oscillator stability.
and RF). But that would be too expensive. I am cutting corners with
2 layers. Perhaps i am just lucky with the one working board.
linnix
Oct 27, 2012, 2:42:43 PM10/27/12
to
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.
lang...@fonz.dk
Oct 27, 2012, 2:48:50 PM10/27/12
to
-Lasse
linnix
Oct 27, 2012, 2:52:30 PM10/27/12
to
MC13202? That might force us to switch part.
lang...@fonz.dk
Oct 27, 2012, 3:10:41 PM10/27/12
to
seems to indicated that is wouldn't be necessary but with the
switchable load caps and temperature measurement I guess you could
-Lasse
Joerg
Oct 27, 2012, 4:14:38 PM10/27/12
to
Four (!) different ground planes? That is usually a recipe for disaster.
> ... But that would be too expensive. I am cutting corners with
> 2 layers. Perhaps i am just lucky with the one working board.
As Lasse wrote, check for correct burden caps. They may very well have
to be different between crystal versions. If the burden caps are wrong
oscillation start may be recalcitrant and your frequency can we off.
Easy way to check if you don't have a good frequency counter: Program a
timer to spit out 1MHz. Then borrow a shortwave receiver, pull in WWV or
WWVB or 5, 10 or 15MHz, listen to the beat. If the beat is in the kHz
range you won't be a happy camper with channel lock up at 2.45GHz.
--
Regards, Joerg
http://www.analogconsultants.com/
Jeff Liebermann
Oct 27, 2012, 7:09:33 PM10/27/12
to
On Sat, 27 Oct 2012 10:22:23 -0700 (PDT), linnix
<m...@linnix.info-for.us> wrote:
>Also, the 1/4 length for 2.5GHz is 3cm. Most WiFI antenna seems to be
>bigger. Are they 3/4 length? Would 1-1/4 be better? We are just
>using a wire coiled on top of the PCB.
Others have addressed the crystal issue, so I'll do the antenna.
<m...@linnix.info-for.us> wrote:
>Also, the 1/4 length for 2.5GHz is 3cm. Most WiFI antenna seems to be
>bigger. Are they 3/4 length? Would 1-1/4 be better? We are just
>using a wire coiled on top of the PCB.
Designer’s Guide to LPRF
<http://www.ti.com/lit/sg/slya020a/slya020a.pdf>
See Pg 39 for links to specifics on the various antenna styles.
Antenna Selection, quick reference guide
<http://www.ti.com/lit/an/swra351/swra351.pdf>
Antenna Selection Guide (new version)
<http://www.ti.com/lit/an/swra161b/swra161b.pdf>
Antenna Selection Guide (old version)
<http://www.prochild.co.kr/board/files/tb_3/AN058%20Antenna%20Selection%20Guide%20swra161.pdf>
Selecting antennas for low-power wireless applications
<http://www.ti.com/lit/an/slyt296/slyt296.pdf>
When you disclose what you're trying to accomplish, and what
limitations are involved (size, cost, placement, aesthetics, range,
data rate, proximity to metals, etc), perhaps I can offer some clues
as to which would be "better".
Incidentally, your wire coiled on top of the PCB might work if you're
lucky, but a well controlled and properly modeled antenna system would
probably be more consistent and more reliable.
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Martin Riddle
Oct 27, 2012, 10:15:19 PM10/27/12
to
"linnix" <m...@linnix.info-for.us> wrote in message
news:b7f16eac-a877-4609...@b9g2000pba.googlegroups.com...
problems for crystals, especially under the crystal.
Cheers
m...@linnix.info-for.us
Oct 28, 2012, 1:24:26 PM10/28/12
to ne...@analogconsultants.com
m...@linnix.info-for.us
Oct 28, 2012, 1:44:55 PM10/28/12
to
On Saturday, October 27, 2012 4:09:31 PM UTC-7, Jeff Liebermann wrote:
> On Sat, 27 Oct 2012 10:22:23 -0700 (PDT), linnix
>
> <m...@linnix.info-for.us> wrote:
>
>
>
> >Also, the 1/4 length for 2.5GHz is 3cm. Most WiFI antenna seems to be
>
> >bigger. Are they 3/4 length? Would 1-1/4 be better? We are just
>
> >using a wire coiled on top of the PCB.
>
>
>
> Others have addressed the crystal issue, so I'll do the antenna.
>
>
>
> Designer�s Guide to LPRF
> On Sat, 27 Oct 2012 10:22:23 -0700 (PDT), linnix
>
> <m...@linnix.info-for.us> wrote:
>
>
>
> >Also, the 1/4 length for 2.5GHz is 3cm. Most WiFI antenna seems to be
>
> >bigger. Are they 3/4 length? Would 1-1/4 be better? We are just
>
> >using a wire coiled on top of the PCB.
>
>
>
> Others have addressed the crystal issue, so I'll do the antenna.
>
>
>
>
> <http://www.ti.com/lit/sg/slya020a/slya020a.pdf>
>
> See Pg 39 for links to specifics on the various antenna styles.
>
>
>
> Antenna Selection, quick reference guide
>
> <http://www.ti.com/lit/an/swra351/swra351.pdf>
>
>
>
> Antenna Selection Guide (new version)
>
> <http://www.ti.com/lit/an/swra161b/swra161b.pdf>
>
>
>
> Antenna Selection Guide (old version)
>
> <http://www.prochild.co.kr/board/files/tb_3/AN058%20Antenna%20Selection%20Guide%20swra161.pdf>
>
>
>
> Selecting antennas for low-power wireless applications
>
> <http://www.ti.com/lit/an/slyt296/slyt296.pdf>
>
>
Thanks. I'll do more reading.
> <http://www.ti.com/lit/sg/slya020a/slya020a.pdf>
>
> See Pg 39 for links to specifics on the various antenna styles.
>
>
>
> Antenna Selection, quick reference guide
>
> <http://www.ti.com/lit/an/swra351/swra351.pdf>
>
>
>
> Antenna Selection Guide (new version)
>
> <http://www.ti.com/lit/an/swra161b/swra161b.pdf>
>
>
>
> Antenna Selection Guide (old version)
>
> <http://www.prochild.co.kr/board/files/tb_3/AN058%20Antenna%20Selection%20Guide%20swra161.pdf>
>
>
>
> Selecting antennas for low-power wireless applications
>
> <http://www.ti.com/lit/an/slyt296/slyt296.pdf>
>
>
>
> When you disclose what you're trying to accomplish, and what
>
> limitations are involved (size, cost, placement, aesthetics, range,
>
> data rate, proximity to metals, etc), perhaps I can offer some clues
>
> as to which would be "better".
>
However, the PFD devices are likely battery powered, and some might be buried underground with external antenna. Some handheld remote unit can have a weak wire antenna, as they are mobile and can be moved closer to the coordinator.
I am using the nearby smart electrical meters as RSSI test. The coordinator can pull in 80% signals within 50m, so the range is fine. My working prototype can pull in around 20% of the packets from the smart meters, and 80% from the coordinator. So, the prototype board is good enough, if only we can reproduce them reliablely.
The coordinator and underground sensor can cost more, but the remote units must be low cost. BOM should be less than $10.
Oliver Betz
Oct 29, 2012, 7:38:48 AM10/29/12
to
"lang...@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)
>> > 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
probe or an output not connected to the crystal.
Oliver
--
Oliver Betz, Munich
despammed.com is broken, use Reply-To:
Oliver Betz
Oct 29, 2012, 7:38:52 AM10/29/12
to
"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?
[...]
>Make sure the board is cleaned properly. The No clean flux can cause
>problems for crystals, especially under the crystal.
about?
Jamie
Oct 29, 2012, 11:35:41 AM10/29/12
to
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
> "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
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
m...@linnix.info-for.us
Oct 29, 2012, 1:28:43 PM10/29/12
to ngs...@z1.oliverbetz.de
On Monday, October 29, 2012 4:38:50 AM UTC-7, Oliver Betz wrote:
> "lang...@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
> "lang...@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
>
>
> >> 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.
> >> 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.
>
Jon Elson
Oct 29, 2012, 7:12:16 PM10/29/12
to
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
>
> 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.
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
Jon Elson
Oct 29, 2012, 7:19:09 PM10/29/12
to
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.
> "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?
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
Oliver Betz
Oct 30, 2012, 5:01:42 AM10/30/12
to
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?
>
[...]
>>>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
>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..
much more uncertainty.
Oliver
--
Oliver Betz, Munich (oliverbetz.de)
upsid...@downunder.com
Oct 30, 2012, 5:38:35 AM10/30/12
to
On Mon, 29 Oct 2012 12:38:52 +0100, Oliver Betz <ob...@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.
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
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.
Oliver Betz
Oct 30, 2012, 8:05:25 AM10/30/12
to
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)
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)
Jeff Liebermann
Oct 30, 2012, 12:38:29 PM10/30/12
to
On Sat, 27 Oct 2012 22:15:19 -0400, "Martin Riddle"
<marti...@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,
<marti...@verizon.net> wrote:
>Make sure the board is cleaned properly. The No clean flux can cause
>problems for crystals, especially under the crystal.
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.
m...@linnix.info-for.us
Oct 30, 2012, 3:30:39 PM10/30/12
to
> 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.
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.
linnix
Nov 10, 2012, 1:20:22 PM11/10/12
to
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.) 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...
> > 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
>
>
> 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:
> 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.
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.
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