Motorola MC68HC11 Crystal
It seems some Crystal experts are on line, so here goes with my question.
I have this microcomputer circuit (attached) that is in a Motorola
Systems Saber radio. It contains a 68HC11 uC that requires Y400 which
is a 7.3728 MHz crystal. Motorola no longer provides an OEM replacement
for this part number 4805664G32. The description is simply "XTAL
ANTIRES". -- Is that Parallel Resonant? These are those tubular 3 x 8 mm
style like the 32Khz crystals used in early watches.
There are two critical stability requirements of this crystal. _First
_it runs the external RS232 programmer at 9600 baud. If bad the radio
cannot be read or written to, and secondly the harmonics could fall on
operating channels. The network of Q403/L400 and C409 are to shift/pull
the frequency where a known harmonic might occur. -- I don't know the
normal stray load this network imparts.
So far I have purchased some generic crystals from e-bay but they don't
seem to be solving the immediate problem which is serial communications
error.
The crystal I removed from circuit oscillated at 7.3708 MHz per the CW
zero beat on my Icom shortwave radio. (I know, yes, it is set to WWV)
or 2 KHz low. The 10 replacement crystals sampled in at around 2.47 KHz
low. An OEM crystal that I have (the last one) 4.36 KHz low. In my
estimation, these parts should be within 30 ppm or +/- 222 Hz
I do not know if the crystal pull network is running when I made these
measurements. It is a possibility. It is switched in and out depending
upon the radio RX frequency. I have no control over those until the
radio is read and rewritten to which I cannot in this condition.
The E-bay generic parts:
Frequency: 7.3728Mhz
Frequency Tolerance: ±30ppm
Load Capacitance: 18pF
Mounting Type: Through Hole
Am I using the wrong load capacitance for the application?
Here are my assumptions:
CL=(24pf x 24pf)/24pf+24pf) + 6pf (stray is a guesstimate) = 18 pf
There is not enough board space to add parts. My estimation of stray
capacitance may be high.
I am trying to get to square one and buy the correct parts. Or maybe
this is as good as it gets and my problem is elsewhere?
--
Joe Leikhim
Leikhim and Associates
Communications Consultants
Oviedo, Florida
407-982-0446
Hi
First off, the programmer will work with any of the crystals you are talking about.
You should be fine at 0.1% which would be +/- 7.4 KHz relative to 7.3728 MHz.
Indeed you should find that serial com will work fine at offsets even greater than this.
In terms of birdies - does the radio work? If not is it an IF issue or a front end problem?
If none of the replacement crystals oscillate, that’s probably a good sign that the problem
is not the crystal …..
Bob
On Mar 5, 2019, at 5:58 PM, Joe Leikhim jleikhim@leikhim.com wrote:
It seems some Crystal experts are on line, so here goes with my question.
I have this microcomputer circuit (attached) that is in a Motorola Systems Saber radio. It contains a 68HC11 uC that requires Y400 which is a 7.3728 MHz crystal. Motorola no longer provides an OEM replacement for this part number 4805664G32. The description is simply "XTAL ANTIRES". -- Is that Parallel Resonant? These are those tubular 3 x 8 mm style like the 32Khz crystals used in early watches.
There are two critical stability requirements of this crystal. _First _it runs the external RS232 programmer at 9600 baud. If bad the radio cannot be read or written to, and secondly the harmonics could fall on operating channels. The network of Q403/L400 and C409 are to shift/pull the frequency where a known harmonic might occur. -- I don't know the normal stray load this network imparts.
So far I have purchased some generic crystals from e-bay but they don't seem to be solving the immediate problem which is serial communications error.
The crystal I removed from circuit oscillated at 7.3708 MHz per the CW zero beat on my Icom shortwave radio. (I know, yes, it is set to WWV) or 2 KHz low. The 10 replacement crystals sampled in at around 2.47 KHz low. An OEM crystal that I have (the last one) 4.36 KHz low. In my estimation, these parts should be within 30 ppm or +/- 222 Hz
I do not know if the crystal pull network is running when I made these measurements. It is a possibility. It is switched in and out depending upon the radio RX frequency. I have no control over those until the radio is read and rewritten to which I cannot in this condition.
The E-bay generic parts:
Frequency: 7.3728Mhz
Frequency Tolerance: ±30ppm
Load Capacitance: 18pF
Mounting Type: Through Hole
Am I using the wrong load capacitance for the application?
Here are my assumptions:
CL=(24pf x 24pf)/24pf+24pf) + 6pf (stray is a guesstimate) = 18 pf
There is not enough board space to add parts. My estimation of stray capacitance may be high.
I am trying to get to square one and buy the correct parts. Or maybe this is as good as it gets and my problem is elsewhere?
--
Joe Leikhim
Leikhim and Associates
Communications Consultants
Oviedo, Florida
407-982-0446
<Y400 Circuit.JPG>_______________________________________________
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and follow the instructions there.
Async communications will usually tolerate an timing error of about 0.5 bit
time in 10 bits or about 5%. So if your oscillator is within 1% (10,000
ppm) you should be OK in that regard.
I suspect your serial communication problem is coming from someplace else.
Maybe the radio needs real RS-232 voltages, or you have a bad interface
chip or power supply for the RS-232, or you need a null modem cable that
swaps the Rx and Tx data lines.
On Tue, Mar 5, 2019 at 6:05 PM Joe Leikhim jleikhim@leikhim.com wrote:
It seems some Crystal experts are on line, so here goes with my question.
I have this microcomputer circuit (attached) that is in a Motorola
Systems Saber radio. It contains a 68HC11 uC that requires Y400 which
is a 7.3728 MHz crystal. Motorola no longer provides an OEM replacement
for this part number 4805664G32. The description is simply "XTAL
ANTIRES". -- Is that Parallel Resonant? These are those tubular 3 x 8 mm
style like the 32Khz crystals used in early watches.
There are two critical stability requirements of this crystal. _First
_it runs the external RS232 programmer at 9600 baud. If bad the radio
cannot be read or written to, and secondly the harmonics could fall on
operating channels. The network of Q403/L400 and C409 are to shift/pull
the frequency where a known harmonic might occur. -- I don't know the
normal stray load this network imparts.
So far I have purchased some generic crystals from e-bay but they don't
seem to be solving the immediate problem which is serial communications
error.
The crystal I removed from circuit oscillated at 7.3708 MHz per the CW
zero beat on my Icom shortwave radio. (I know, yes, it is set to WWV)
or 2 KHz low. The 10 replacement crystals sampled in at around 2.47 KHz
low. An OEM crystal that I have (the last one) 4.36 KHz low. In my
estimation, these parts should be within 30 ppm or +/- 222 Hz
I do not know if the crystal pull network is running when I made these
measurements. It is a possibility. It is switched in and out depending
upon the radio RX frequency. I have no control over those until the
radio is read and rewritten to which I cannot in this condition.
The E-bay generic parts:
Frequency: 7.3728Mhz
Frequency Tolerance: ±30ppm
Load Capacitance: 18pF
Mounting Type: Through Hole
Am I using the wrong load capacitance for the application?
Here are my assumptions:
CL=(24pf x 24pf)/24pf+24pf) + 6pf (stray is a guesstimate) = 18 pf
There is not enough board space to add parts. My estimation of stray
capacitance may be high.
I am trying to get to square one and buy the correct parts. Or maybe
this is as good as it gets and my problem is elsewhere?
--
Joe Leikhim
Leikhim and Associates
Communications Consultants
Oviedo, Florida
407-982-0446
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to
http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.
--
--Jim Harman
Greetings Joe,
Except for the difference in the marked frequency, there is no difference between the so-called "parallel resonant" and "series resonant" crystals. There is a minute difference in the physical dimensions and/or the angle of the cut(s) relative to the crystallographic axes to hit the desired frequency. The description of the OEM part "XTAL ANTIRES" shows that it is "parallel resonant" with the capacitance specified by the crystal manufacturer (typically 20 pF (sometimes less), 30 pF, or 50 pF) appearing in parallel with the crystal. This is the reason behind the use of a small-value variable capacitance in parallel with the crystal to trim the frequency to exactly that specified or desired at constant temperature though the trim range is relatively small. The design of crystals is something of a "black art".
The so-called "series resonant" crystals are sometimes described as for use in a "resonant" mode while the so-called "parallel resonant" crystals are sometimes described as for use in an "anti-resonant" mode. This is technical gibberish but the "parallel resonant" and "series resonant" descriptions are a useful guide for the designer of the amplifier in which the crystal acts as narrow band filter in the feedback circuit and controls the frequency of the resultant oscillation.
There are many considerations, such as the drive level (particularly for physically very small and very large crystals!) which have to be considered but if the equipment used to work correctly in the long term it is unlikely that there is a problem with the crystal. From your description, I doubt if the fault is in the crystal and you will need to look elsewhere for the fault.
I hope that this may help you.
Regards,
Roger
On Tue, 5 Mar 2019 17:58:58 -0500, Joe Leikhim jleikhim@leikhim.com wrote:
It seems some Crystal experts are on line, so here goes with my question.
I have this microcomputer circuit (attached) that is in a Motorola
Systems Saber radio. It contains a 68HC11 uC that requires Y400 which
is a 7.3728 MHz crystal. Motorola no longer provides an OEM replacement
for this part number 4805664G32. The description is simply "XTAL
ANTIRES". -- Is that Parallel Resonant? These are those tubular 3 x 8 mm
style like the 32Khz crystals used in early watches.
There are two critical stability requirements of this crystal. _First
_it runs the external RS232 programmer at 9600 baud. If bad the radio
cannot be read or written to, and secondly the harmonics could fall on
operating channels. The network of Q403/L400 and C409 are to shift/pull
the frequency where a known harmonic might occur. -- I don't know the
normal stray load this network imparts.
So far I have purchased some generic crystals from e-bay but they don't
seem to be solving the immediate problem which is serial communications
error.
The crystal I removed from circuit oscillated at 7.3708 MHz per the CW
zero beat on my Icom shortwave radio. (I know, yes, it is set to WWV)
or 2 KHz low. The 10 replacement crystals sampled in at around 2.47 KHz
low. An OEM crystal that I have (the last one) 4.36 KHz low. In my
estimation, these parts should be within 30 ppm or +/- 222 Hz
I do not know if the crystal pull network is running when I made these
measurements. It is a possibility. It is switched in and out depending
upon the radio RX frequency. I have no control over those until the
radio is read and rewritten to which I cannot in this condition.
The E-bay generic parts:
Frequency: 7.3728Mhz
Frequency Tolerance: ±30ppm
Load Capacitance: 18pF
Mounting Type: Through Hole
Am I using the wrong load capacitance for the application?
Here are my assumptions:
CL=(24pf x 24pf)/24pf+24pf) + 6pf (stray is a guesstimate) = 18 pf
There is not enough board space to add parts. My estimation of stray
capacitance may be high.
I am trying to get to square one and buy the correct parts. Or maybe
this is as good as it gets and my problem is elsewhere?
--
Joe Leikhim
Leikhim and Associates
Communications Consultants
Oviedo, Florida
407-982-0446
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
and follow the instructions there.