DSP-10 Hardware Notes
Bob Larkin, W7PUA
23 March, 2002


The following are a collection of notes that relate to the hardware
used with the DSP-10 project. They reflect the efforts of many people
that have participated in the project. I will attempt to acknowledge
the various contributors, but my apologies to those that I miss!
Unmarked items were mine, as were any mistakes.  Thanks to all.

This list is up-to-date as of March 2002.  In addition to these
notes, there is a second file, dsp10n45.txt, that has what were
originally called "assembly notes," but cover a variety of subjects
in that area.  Additionally, further data may be available on the
internet. As of March 2002 the URL was
http://www.proaxis.com/~boblark/dsp10.htm.
Detailed assembly notes from Steve Bible, N7HPR are linked from that
page, for instance. These can be VERY helpful for the actual PC Board
assembly.It also has material that was not available at publication
time. If the Web page location is changed it will still include the
word ABCDSP10ABCD that may be helpful for locating it with a search
engine!

C71 TEMPERATURE COEFFICIENT The wrong temperature coefficient was
specified for C71. If your second conversion PLL does not work
properly as it warms up (check the tuning voltage at the junction of
C62 and R54), yours is not an NPO. The correct part is Digi-Key
PCC221CGCT-ND, which is 0805 size. D-K does not list a 1206 (bigger)
size. Mouser lists the 1206 size as 140-CC502N221J. I have not tried
these, but they should be fine and are now shown on the spread sheet.
If you have access to any 220 PF NPO put it in there. There is a
reasonable amount of space in the area around C71, and so a leaded
cap would work. The little "via" by the one end of C71 is ground, if
that helps. You should not need to remove the board from its
mountings. (Thanks to Beb, W7SLB, and Larry, W7SZ, for the help with
solving the problem.)

C220 and C221: Oct QST shows these as surface mount, but they really
need radial leads. It also wouldn't hurt to get some margin on the
Voltage. I would suggest 47 uF at 25+ Volts, like Mouser 140-XRL25V47
or Radio Shack 272-1027. (W7PUA)

J208 8-Pin DIN: The part number was not listed. Radio Shack does not
have this one. I got mine from Digi-Key, CP-1280. Interestingly,
Radio Shack sells the mating plug, 274-026. (W7PUA)

SPACER LENGTH: I would sugget you lower the main PCB and the EZ-Kit
both by making the spacer under the boards 3/16 inch (5 mm) instead
of the 1/4 inch listed in Fig 11. These can be aluminum if you stick
these to the boards with a TINY spot of RTV. I used Digi-Key J166
standoffs.  (W7PUA)

IMPORTANT CORRECTION: Two of the values of chip cap, the 470 pF and
the 0.01 uF have pads on the board for 0805 size parts. I have been
telling people that they can use the 1206 size. This is problematic,
since inspection becomes very difficult. Please use the 0805 size for
these two values. They are all bypass caps and can be 10 or 20%, and
any ceramic types (Z5U, X7R, etc.) The supplier part numbers now on
the spread sheet, for the 0805 parts, are: 470 pF: C9,...,C136
Digi-Key PCC471BNCT 0.01 uF: C7,...,C142 Mouser 140-CC501Z103M Both
values can be bought from either supplier. Check their catalogs.
(W7PUA)

Surface Mount (SMT) Inductors The 32CS SMT inductors, listed in the
original parts list, are being phased out by Toko. Some values are
still available from Digi-Key, others may not be. One alternative is
the API-Delevan Series 1210 Unshielded inductors, also available from
Digi-Key. I bought some of each of the five values used in the DSP-10
and tested them. The differences were measureable, but not big. For
the DSP-10 I feel that the API-Delevan parts should work fine. The
biggest drawback for the API-Delevan parts is that their values are
NOT marked on the case. We have lived with this situation on the
caps, but it does require extra care. Soldering, size, and ruggedness
all seem fine. The API-Delevan parts are less expensive. (W7PUA)

Mini-Circuit Orders should reference the QST article, and they may be
able to waive minimum-order requirements. Thanks, MiniCircuits. (This
from W5RXP)

10 MHZ CRYSTAL First, a translation of the International Crystal
433463 part number: 4 Custom Series 3 Calibrate at 26 deg C 3
Frequency range of 3 to 10.99 MHz 4 High Accuracy Specs (Within 10
PPM at 26 deg, and within 20 ppm -30 to +60 deg C) 6 FM-1 Holder
(HC-43/U, same size as HC-18/U) 3 20 pF load capacity Note that if
you order this crystal you need to specify the exact 10.000MHz
frequency along with the part number. International Crystal told me
that this crystal is $20.59 and delivery is 2 to 3 weeks.

The question comes up as to the suitability of low-cost computer
crystals that are widely available for 10 MHz. First, I would not
hesitate to put one in if you do not have a high quality crystal
available. The problems that you can expect are temperature stability
and the initial frequency setting. The frequency can adjusted with
C110 along with a change in C109 value (more capacity is a lower
frequency of oscillation.) But, the temperature stability can be
anything with the cheap crystals. You can't do much about it without
changing crystals.

An update on low-cost crystals: As an experiment, I put one of the
Epson CA-301 10 MHz crystals in at Y101. The potential advantages are
their available from Digi-Key (Part No SE3420) and cost of only
$1.17.

The CA-301 oscillated fine. I was able to put it on frequency at room
temperature by placing 10 pF leaded capacitors across both C108 and
C109 (in addition to the caps that are already there). I warmed it up
to 35 deg C and measured the 2-meter frequency change as 58 Hz per
deg C. This suggests that you could keep the 2-meter frequency within
+/- 600 Hz, over a 20 deg range, which is certainly useable. Remember
this is a sample of 1 and that they are spec'd rather loosely. But
experience with the CA-301's has generally suggested they are better
quality than most 'computer' crystals. (W7PUA)

Eventually, you will want to use an external 10 MHz reference. Being
'exactly' on frequency is a goal that we all should look towards. My
experience with the Brooks Shera GPS Controller (reference 10 in
September QST) has been excellent. (W7PUA)

Motorola MC145170D2 PLL Motorola upgraded the part to revision 2.
This changes the part number for U7 to MC145170D2. You do NOT want
the same part ending in DT2 as this is the package with 0.025 inch
pin spacing---very tight! If you have MC145170D1 it will work fine
(they are what I used.) (W7PUA)

CORRECTIONS:
1 - The connections on the EZ-Kit to P3, Pin 31 and P3, Pin 32 are
backwards. A corrected portion of QST Fig 11 shows the change. It
also reflects on QST Fig 10, but no wiring is changed.

2 - R49 in the schematic and the part information should be 47K (not
1.8K.)

3 - R21 should be 10K (not 100K); this causes the gain to be 20 dB
too high.

4 - R108 should be 4.7K Ohms (not 470). Some combinations of U107 and
U104 have been found to have the data line at U104 switching too
early. These are cascaded shift registers and the timing is quite
close. The R108 resistor change slows down the data line going to
U104, making the timing less critical.

5 - C71 must be NPO temperature stable type.


IMPROVEMENTS:
1 - R16 can be changed from 10K to 6.8K. This centers the output
Voltage on U10A better. I am unaware that the old value had actually
caused any clipping on U10A output, though.

2 -  U15 Mixer Grounding can cause major degradation in sensitivity.
It is very important that this is dealt with! All the information is
on U15 modification page, in a separate file u15_mod.htm that is
readable on any Web Browser. The modification is simple but the
improvement can be big. (W7PUA)


IMPORTANT The silk-screen legend is backwards for the 78L05
regulators, U13 and U103. The flat sides of both TO-92 packages
should be towards the top of the board. There is no problem in
installing the parts, of course. The sketch of the package included
with the board is correct. (Thanks to KD7TS for catching this.)

Note 8 of the Assembly Notes says that all chip caps can be 1206
size. This is NOT true for the 0.01 uF and 470 pF values. These
should be 0805 size. Also the 0.01 uF part number in the 4.1 addendum
to the Assembly Notes is for the larger size. (W7PUA)

"SR105" Diode When the DSP program is first started and before the PC
program is run, the DSP-10 can come up with BOTH transmit and receive
turned on. This sets up a loop that oscillates at full power! Very
bad. My DSP-10 shows about +16 or +17 dBm out. The happens because
the shift registers (U107, U108) come up uninitialized. The eventual
solution will be to program an EPROM that includes the setting of the
shift registers at DSP startup. Here is a work-around until you have
an EPROM version: Acquire a Schottky diode and solder the cathode
(bar end) to the junction of R132 and Q104-collector. Solder the
anode (non-bar) end to the junction of R130 & R131 (base of Q103). It
must be a low barrier voltage diode like the Schottky, but it can be
either a rectifier or small-signal type. I used a SR105 from
Digi-Key, but I notice that Radio Shack has 1N5817-1N5819 or
1N5820-1N5822 on special order status. W7LHL suggested that a 1N34
type of germanium could work also. This work-around prevents the
'transmit' from being enabled when 'receive' is enabled.

To assist in the assembly of the main PC Board, there is an Assembly
Part List (file dsp10pd2.txt) that has a separate line for each part
on the board. The value and location of each part is listed in inches
and mm. This is an assembly and test aid and not for purchasing
parts. Use the 'Part Buying Information' below for this.

All of the part buying information is being moved to a single page of
Part Buying Information. I will try to indicate the update status of
the part page here. To that end, note that the Spread Sheet of buying
information, put together by Rich, W5RXP has been updated, as of 28
Oct 99. Also more part source links and information have been listed
and the 0805 chip correction, listed above, was added.

If you are using the Epson 10 MHz crystal for Y101, rather than the
ICM crystal listed in QST, you will need to add capacitors across
C108 and C108 as described on Parts Page.
 
The ground connection to the EZ-KIT Lite board is not shown
explicitly. The negative lead for the power will probably handle the
grounding, but two short ground wires from P3-1 and P3-50 to the box
will make sure there is a good ground for the digital wires. No
problem has been reported for the grounding of the analog lines. The
10 to 20 kHz range is reasonably immune from such problems. If there
is any question, you can catch an analog ground in the area around J1
and J2 on the EZ-KIT board.
 
On the subject of P3. The pin numbering for P3 on the EZ-KIT board is
confusing. This seems to relate to the PCB layout program that was
used. Any reference to P3:2-xx should be P3-xx. The ':2' and ':1' are
not needed.
 
Be careful in winding the toroids. Too tight and they will crumble
into pieces. The best procedure is to just bring the turns snug.
After the toroid is finished it can be helpful to cover it with
"Polystyrene Q-Dope" (GC Electronics 10-3702).
 
By keeping the voltage going to the EZ-KIT to 9 Volts, the
temperature of the U6 regulator on the EZ-KIT is hot, but not
excessive, as long as the overall box is at room temperature. To
provide some margin, one can attach a piece of metal between the
regulator and the box. If this is bent at right angles it can be
fastened with machine screws.