From: rdewan@casbah.acns.nwu.edu (Rajiv Dewan)
Subject: Review (long) of W9GR DSP Kit from QST
Organization: Northwestern University, Evanston Illinois.
Date: Sun, 6 Sep 1992 17:35:51 GMT

                   Review of W9GR DSP Kit
                     Rajiv Dewan  AA9CH
                         
After ordering the kit the day I got my copy of the Sept issue of
QST, I received the kit on Friday last (9-4) in mail.  I had
ordered the basic kit with the default De-noiser and Autonotcher filter
ROM and a 750Hz center frequency, 200Hz BW CW filter ROM. 

As a detail description of the unit is in "Low cost Digital
Signal Processing for the Radio Amateur," in the September 1992 issue
of the QST, only performance and construction experience are
included in this review.

Performance:
------------
  De-noiser: The default ROM has a LMS implementation of a FIR
filter that is used to subtract all serially uncorrelated parts
(hash and static) from the input.  It works well.  I tested it on
CW and SSB on 40 and 80 meters.  On the day of test, 80m band had
S7 QRN at my location.  For SSB signals 2 units or more better
than noise, the unit removed enough of the QRN so that in terms
of noise the QSO sounded like FM with 90% full quieting.  Of
course, characteristic HF fades were still there and in fact more
noticeable now that the noise was greatly reduced.  It makes it
significantly less tiring and more pleasant to listen to the
low-low bands (or the top bands in previous terminology.) The
effect is less dramatic as the signals level begins to approach
the noise level.  For signals 1 S unit above the noise, the
improvement is still impressive.  For weaker signals the
improvement is there but is marginal.  CW performance was better
as weak signals had a greater improvement that observed with SSB. 

  Autonotcher:  It rapidly acquires heterodynes that are 2 S units
above the noise and all you hear is a click.  I tried this on CW
and all I heard were key-clicks.  To simulate multiple
heterodynes I tuned to a busy portion of the CW band and used a
wide filter in the rig.  Stronger CW stations are acquired
quickly.  The weaker ones take some time.  The delay is
noticeable and interesting.  It takes a while for the
coefficients in the filter to reach appropriate values to notch
the weak CW stations out.

  CW filter: 750Hz center, 200Hz BW.  The filter has a tremendous
shape factor.  I tuned in a S9+ cw station and tried tuning
around.  The rate of change of amplitude is impressive.  As I
tuned off the zero beat frequency, the signal just falls off a
cliff.  I have 270 and 500Hz filters in the rig and their shape
factor is no where near as low.  I am not sure that is an
un-mitigated blessing even in situations where a 200Hz filter
would be desirable.  Contests come to mind.  It is not uncommon
for the answering station to be a little off.  Steep skirts can
be a disadvantage.  It would be nice to have a choice of shape
factors.  

Construction:
-------------
The kit includes:
*  A double layered PC board with soldering mask and plated
through holes. The solder mask covers all of the board except the 
soldering pads. This makes it more difficult, although not impossible, 
to have solder bridges.
*  All on board components including IC sockets and heat sink for
the 5v regulator.
*  DPDT on/off switch, a SPDT BIO switch, momentary contact reset
switch, audio level pot and the led bargraph display.  The DPDT
is micro-mini whereas the SPDT is mini - opposite form factors of
what I would have preferred.  A micro-mini SPDT for BIO was obtained from
Radio Shack.  The audio pot furnished is enormous.  I substituted
it with a miniature version.  
*  Instructions and some extra order forms.

It took about three hours to put all the components on the board.
This included a half hour wasted on diddling with a wire wrap socket
to turn it into a 90 degree socket for the display.  This is used
for the led bar display which is in a 20 pin dip package.  I bent
the pins carefully and tried to install on the board.  The holes
are just a little bit too small.  It would be OK for a couple of
leads but trying to force 20 brittle and bent wire wrap legs
simultaneously in the pc board was beyond my skills.  I did not
want to drill out the plated through holes.  The botom
line: the socket was filed in the circular container.  I soldered
the bar display directly to the board in the following fashion.
I bent the front row of pins and soldered them to the board.  I
used resistor cut-off wires to connect the back row pins to the
holes in the PC board.  I found it easier to first solder the wires
to the board and then bend them just enough to touch the
appropriate pin of the display.  It works and makes a rigid
connection.  A side advantage of this approach is that the
display does not stick out of the front panel as much as it does in
the QST unit and looks neater.

After I wired it all up, I tested the unit.  No go.  The leds
would light up and go out and then a few would stay lit.  No
audio output.  Examination of the board with a magnifying glass
revealed a few suspect solder points.  I went over them and then
plugged it back in.  It worked.

Without a box and any extra bypassing, the unit produces S9+60 hash on 2m
when monitored with a HT with a rubber duck antenna a few feet
away and S5 hash when monitored with a discone antenna in the
attic.  A box and 0.01 caps across the audio leads
and the 12v power connection reduced the hash to the point that is not
detectable by the discone antenna and is S2 when monitored with a
rubber duck antenna inches away.  This is less than the hash
generated by my PC.  I used the Radio Shack box recommended in
the article.  I cut the sides to reduce its height by an inch or
so.  The reduced size is adequate and makes for a much more
compact unit.  Gray paint for the face to match my Kenwood rig,
Datak dry tranfer lettering and a clear coat finished off the cabinet.

New Version:
------------
The package from Quantics included information about a
multiple-filter version in which the TMS320M10 has firm ware for
10 different filters written in.  The filters include 
(Quantics description):
   - De-noiser and Notch filter 
   - Simultaneous De-noiser and notch filter
   - Optimized (some what more effective) de-noiser
   - Optimized notch filter
   - 400 Hz center, 200Hz BW filter
   - as above but 600 Hz center
   - as above but 750 Hz center
   - as above but 1000 Hz center
   - 750 Hz center, 30Hz BW
   - HF packet (1600/1800Hz) and RTTY (2125/2295Hz) filter

The unit with multi-filter chip costs $125 and the cost of
upgrade from QST like unit to the multi-filter costs $45.

More information can be obtained from Quantics (address is in
Sept QST).

I have no connection with W9GR or Quantics.  I am just a
satisfied QST reader and home-brewer.

Rajiv
aa9ch
address: r-dewan@nwu.edu, aa9ch@w8lvn.il.usa.na
Newsgroups: rec.radio.amateur.misc