Transcript PSK31: A Short Primer

Fun on the Waterfall
A Operating PSK-31
Presented to the QRP Forum
2001 ARRL South Western Division Convention
Barry L. Geipel – AD6HR
Lake Perris QRP Society
September, 2001
Overview
• Invented by Peter Martinez, G3PLX
• PSK31 is a new digital mode which utilizes the
processing power of computers and sound cards.
• Software on the computer converts inputted text
to audio level wave forms which can be fed into
most standard SSB radios.
• The same software listens to the output of the
radio and decodes the audio signals back into
text.
Overview
• PSK31 is designed for conversational
QSO’s.
• There is no error correction built into the
mode, so you can never count on the
message being received error free.
• Therefore it is not good for automated mail
boxes and the like.
Technology
• PSK31 uses phase shift keying to produce
logical zeros and ones.
• The bandwidth and baud rate are both
31Hz (therefore the name, PSK31)
• Characters are formed using combinations
of zeros and ones in a coding scheme
called Varicode.
Varicode
• The end of a character is signaled by two
or more consecutive zeros.
• Varicode is much like the Morse code in
that the most common characters have the
least number of bits.
Varicode
• However, Varicode supports a much larger
set of characters than Morse, including
upper and lower case alpha characters.
• The shortest characters are all lower case
alpha characters so in casual contacts, do
not use upper case characters since they
take much longer to transmit.
Varicode
NUL
SOH
STX
ETX
EOT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
1010101011
1011011011
1011101101
1101110111
1011101011
1101011111
1011101111
1011111101
1011111111
11101111
11101
1101101111
1011011101
11111
1101110101
1110101011
1011110111
1011110101
1110101101
1110101111
1101011011
1101101011
1101101101
1101010111
1101111011
EM
SUB
ESC
FS
GS
RS
US
SP
!
"
#
$
%
&
'
(
)
*
+
,
.
/
0
1
2
3
4
1101111101
1110110111
1101010101
1101011101
1110111011
1011111011
1101111111
1
111111111
101011111
111110101
111011011
1011010101
1010111011
101111111
11111011
11110111
101101111
111011111
1110101
110101
1010111
110101111
10110111
10111101
11101101
11111111
101110111
5
6
7
8
9
:
;
<
=
>
?
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
101011011
101101011
110101101
110101011
110110111
11110101
110111101
111101101
1010101
111010111
1010101111
1010111101
1111101
11101011
10101101
10110101
1110111
11011011
11111101
101010101
1111111
111111101
101111101
11010111
10111011
11011101
10101011
11010101
Q
R
S
T
U
V
X
Y
Z
[
\
]
^
_
.
/
a
b
c
d
e
f
g
h
i
j
k
l
111011101
10101111
1101111
1101101
101010111
110110101
101011101
101110101
101111011
1010101101
111110111
111101111
111111011
1010111111
101101101
1011011111
1011
1011111
101111
101101
11
111101
1011011
101011
1101
111101011
10111111
11011
m
n
o
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
111011
1111
111
111111
110111111
10101
10111
101
110111
1111011
1101011
11011111
1011101
111010101
1010110111
110111011
1010110101
1011010111
DEL 1110110101
Waveforms
• PSK31 waveform sending a series of
logical zeros.
Waveforms
• PSK31 waveform sending a series of
logical ones.
Getting Started
• Getting started in PSK31 can be quite easy
if you have a few basic components.
• Most hams have everything they need to
get going right away.
• The minimalist system may not be the
most fun, so you will eventually want to
build up a few extra components.
Hardware – minimalist system
• A stable SSB radio capable of tuning the PSK31
frequencies.
• A computer with a 16 bit sound card in the
133Mhz or higher class.
• Audio patch cords.
• Plug the patch cord from your rigs headphone
jack to your computer sound cards mic jack.
• Hold your rigs mike up to your computers
speaker and key the mike when want to transmit.
Hardware – a bit better
• A stable SSB radio capable of tuning the PSK31
frequencies.
• A computer with a 16 bit sound card in the
133Mhz or higher class.
• A audio patch for wired up as before.
• Another audio patch cord with a 100:1 voltage
divider hooked into your rigs mic input.
• Set the VOX level and go!
Hardware – a bit better
• A simple interface cable
• This circuit can often be built into a
standard mic housing.
Hardware – the best
• A stable SSB radio capable of tuning the
PSK31 frequencies.
• A computer with a 16 bit sound card in the
133Mhz or higher class.
• An interface cable appropriate for your
other hardware.
• Depending on the interface cable, you may
also need a free serial port.
Hardware – the best
• Interface cable can be easily built or purchased.
• Uses the serial line to key the rig.
• Isolates the computer side from the radio
preventing RF feedback.
• The Inland Valley Alliance of Amateur Radio
Clubs did a club project to build one of these:
• http://www.geipelnet.com/barry/PSK31.pdf
Software
• Most of the work in PSK31 is done in
software, therefore you will need a PSK31
software package.
• Most of them are FREE!!
• Available on the Web.
• DigiPan (http://members.home.net/hteller/digipan/download.htm)
• WinPSK (http://www.qsl.net/ae4jy/winpsk.htm)
Operating
• Each software package had different interfaces.
You will need to become familiar with the
package you choose.
• Your radio should be tuned to one of the listed
operating frequencies. Your software will show
you a representation of all signals in your radios
bandpass.
• The hardest part of PSK is adjusting the audio
drives for maximum performance.
Operating - receive
• On receive you can adjust the volume
control on the radio until you see the best
quality signal. Your software operating
guide will explain how this is done.
• Some packages allow you to view multiple
signals that are within your rigs bandpass.
Operating - transmit
• Transmitting can be a bit tricky, and for the
most part you will rely on signal reports to
set your output audio correctly.
• In general, you will use your operating
system audio control to adjust the output
volume. A good rule of thumb is that you
want your radio’s ALC meter to just barely
deflect.
Operating - transmit
• When adjusting the output volume, be sure
that you are adjusting the correct port.
Many computers have both a headphone
out and a line out. Both can be used for
PSK31, but each will have separate
controls.
Operating – signal reports
• In PSK31, the most useful signal report is your
IMD (inter modulation distortion) measured in
dB.
• IMD’s are measures using dead air. Most
software will give you an IMD report. You
should strive for an IMD of less than –20 dB.
• The most common cause for a bad IMD is to
much audio drive into the mic.
• The solution is to turn back the audio drive using
your computers audio configuration.
Operating - QRP
• PSK31 has an incredible ability to pull
signals out, therefore we should all strive
to use as little power as possible.
• The experts are saying use 30watts
• Barry says, “Use 5 watts or less!”
Frequencies
• Here is list of suggested operating
frequencies.
1838.15kHz
3580.15kHz
7070.15kHz
14070.15kHz
21080.15kHz
28070.15kHz
28120.15kHz
10137.15kHz
18100.15kHz
24925kHz
Web Resources
• Web Resources:
– General Info:
• http://www.packetradio.com/bbbb.htm
• www.aintel.bi.ehu.es/psk31.html
• psk31.org
– Interface Cables
• http://www.geipelnet.com/barry/PSK31.pdf
• www.packetradio.com/psk31.htm
• www.westmountainradio.com