This is only a preview of the June 1989 issue of Silicon Chip. You can view 44 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
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PADDLE OR
COMPUTER IN
CCW
KEVER
PULSE
PHASE
TRANSMITTER
PULSE
LENGTH
REFERENCE
FREQUENCY
MASTER
FREQUENCY
STANDARD
CCW
FILTER
RECEIVER
REFERENCE
FREQUENCY
MASTER
FREQUENCY
STANDARD
PULSE
PHASE
AUDIO
OUT
PULSE
LENGTH
FILTER
DRIVER
Fig.2: the basic CCW system. The receiving and transmitting stations are
synchronised by signals received from a time and frequency station (eg,
WWVB in the USA or VNG in Australia).
Normally, CW dots, dashes and
spaces begin at random times
depending upon the operator, and
thus the frame length varies to an
unpredictable degree. By sending
CCW so that all dots, dashes and
spaces are multiples of the basic
time unit, the signal will be received within predictable time frames.
Now although this may sound difficult, users report that this technique is usually mastered within a
short time. Naturally, the use of a
keyer or computer to generate
characters makes the job even
easier.
Fig.2 shows the basic CCW
system. In order for CCW stations
to communicate, it is necessary for
both stations to agree in advance on
the operating frequency and the
frame length (normally 0.1 second)
for an operating speed of 12 words
per minute. Since a dot and a space
each require 0.1 seconds, a string
of dots at 12 WPM is a square wave
having a basic frequency of 5Hz.
To establish communications, a
CCW station sends a sequence of
dots , allowing the receiving station
to acquire the signal and synchronise the IF " filter" . Once locked, the filter should remain stable
for hours.
There is great deal more to CCW
than this short article indicates but
it is clear that the technique shows
a lot of potential for amateur experimentation, particularly for long
distance transmissions and EME
(Earth-Moon-Earth) work.
Further reading on CCW
(1). "Coherent CW" ; QST magazine,
May & June 1981.
(2). "What Is Coherent CW? ";
Japanese Ham Radio Journal ,
January 1976.
(3). "Coherent CW : Amateur
Radio's New State of the Art" ; QST
magazine, September 1975 (Ray
Petit).
(4). "Universal Frequency Standard"; Ham Radio magazine ,
February 1974.
(5). The 1989 ARRL Handbook for
Radio Amateurs (page 21-16).
Sangean ATS-803A shortwave receiver
There are a number of receivers available to the
shortwave listener today but most are useless if
you want to listen to CW or SSB transmissions on
the HF bands. This receiver offers continuous
coverage from 150kHz to 30MHz and as a bonus
will pick up the FM broadcast band.
The ATS803A is made in Taiwan
and looks similar to the Sony
ICF-2001 (which is now superseded)
but with a number of refinements
including FM stereo reception via
headphones, variable RF gain control, a tuning knob and a much
larger battery compartment.
The cabinet is well finished in
black plastic, with gold trim on the
tuning knob and brushed aluminium
around the LCD readout. The LCD
readout has 12mm digits and is
very easy to read. Below the
readout is a list of the frequency
ranges for the various shortwave
bands.
Below that again is the control
panel which has 22 buttons. Five of
these select the band: FM (88 to
108MHz), AM, LW (beginning at
150kHz), MW (beginning at 520kHz)
and SW (beginning at 2300kHz).
Tuning can be done in several
ways: (1) you can punch the station
frequency in directly via the
pushbuttons and then hit the "execute" button; (2) you can use the
Start/Stop buttons for scanning upwards from .any frequency; (3) you
can use the up/down buttons or the
tuning knob for manual tuning; or
(4) you can call up one of 14 stored
station frequencies.
RF gain control
For dedicated HF enthusiasts,
the unit has an adjustable RF gain
control, which allows the user to
adjust the receiver sensitivity in
cases where signal overload is a
problem. The provision of a BFO
(beat frequency oscillator) allows
reception of single sideband (SSB)
and CW signals. This feature is of
particular importance for those interested in amateur, aircraft or
marine HF transmissions.
There is also provision for the
connection of a number of accessories, including external antenna, external DC supply (9V at up to
400mA), headphones (stereo for
stereo FM reception, mono for
JU NE 1989
67
AMATEUR RADIO - CTD
The Sangean ATS-803A receiver features fully synthesised digital tuning and
provides continuous coverage from 150kHz to 30MHz in both AM and SSB
modes. As a bonus, it will also pick up the FM broadcast band.
shortwave reception), and a high
impedance output for connection to
a tape recorder.
Other features include a built in
digital clock with alarm (which
allows the receiver to be turned on
at a particular time), and a sleep
timer, which turns the receiver off
after a period settable between 10
and 90 minutes.
The battery compartment takes 6
D-size cells and 2 AA cells for backing up the computer, so that station
settings can be stored. The latter
two cells are not essential to the
radio's operation, which is handy if
you use mains power most of the
time.
What we found
Using the telescopic antenna on
the unit, we had no problem in
receiving the long wave weather
beacons at Sydney, Richmond and
Camden airports. These weather
beacons are particularly useful for
providing accurate weather information.
Using the scan-UP control we
scanned through the AM broadcast
band to the 2MHz marine band,
where most broadcasts are USB.
Specifications
Receiver type: dual conversion
superheterodyne (LW, MW, and
SW).
Intermediate frequencies: AM,
55.845MHz and 450kHz; FM ,
10.7MHz.
IF suppression: AM, 50dB; FM,
60dB.
Shortwave bands
Shortwave 1: 2.30-2.50MHz
Shortwave 2: 3 .20-3.40MHz
Shortwave 3:. 3.90-4.00MHz
Shortwave 4: 4 .75-5.06MHz
Shortwave 5: 5.80-6 .20MHz
68
SILICON CHIP
Shortwave 6: 7. 1 0- 7. 50M Hz
Shortwave 7: 9.50-9 .90MHz
Shortwave 8: 11 .65-12.05MHz
Shortwave 9: 15.10-15.60MHz
Shortwave 10: 17.55-17.90MHz
Shortwave 11: 21 .45-21 .85MHz
Shortwave 12: 25 .60-26.10MHz
Note: these SW bands are selectable in sequence by repeatedly
pressing the SW button.
Long wave band: 1 S0kHz-281 kHz .
FM band: 87.5MHz-108MHz.
AM band: 150kHz-29,999kHz continuous (SSB reception using BFO) .
The BFO allowed good reception of
Sydney Radio on 2182kHz. Working
up through the HF bands we
covered shortwave 1 and 2, then
the 80-metre amateur band, using
the BFO for SSB and CW reception.
At 5.0MHz we were able to
monitor the revamped, privately
operated VNG time signal, although
at greatly reduced signal level compared with the original Lyndhurst
site. 6677kHz provided interesting
listening as many international airports broadcast current meterological conditions on this frequency.
The 40, 20 and 10-metre amateur
bands are also covered, although
we did not hear any 10-metre activity. Towards the upper end of the
receiver coverage we noticed a lack
of signals, although this seemed to
be due to inactivity rather than a
problem with the receiver as we
were able to hear an increase in
background noise when we connected an external long wire
antenna.
FM reception was good, which is
to be expected in any capital city
where signal levels are high, and
stereo separation was quite respectable (quoted specification is 25dB).
Incidentally, stereo FM is only
available via the headphones with
the sound being heard in mono via
the loudspeaker.
Sound quality is acceptable for a
communications receiver and the
tone controls can give an improvement in intelligibility in difficult
reception conditions.
In summary, this receiver is
keenly priced, a good performer,
and offers features that should suit
the enthusiast and dedicated shortwave listener alike. Recommended
retail price is $299.00.
In addition to the instruction
manual, a 60-page service manual
is available which contains all circuit diagrams, voltage charts, parts
lists, PCB foil patterns, alignment
procedures and troubleshooting
flow charts. This we consider a
vital factor for users not located in
capital cities or close to service
facilities.
Our review unit was supplied by
the Australian distributors, Access
Communications Pty Ltd, 33
Alleyne Road, Chatswood, NSW
2067. Phone (02} 406 5311.
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