Tip & How-To about Audio Players & Recorders
PSK31 is arguably the most popular amateur radio
digital mode. It utilized phase-shift-keying to
provide robust, narrow signal width communications,
and requires very little power to QSO the world!
- Use the center of your waterfall. Testing will
show that your transmit (TX) and receive (RX)
will be strongest there. Don’t blindly use 1000Hz
tone or strictly follow the VFO ‘set it and forget it'
concept. You can easily lose 20% or more of
your power on each edge of your pass band.
Pass band centering of the signal will give the
best results of both RX and TX.
-There's no need to have the waterfall streaking
bright red. Set your rig's volume to a low level
(less than 25% of max) and adjust your waterfall
and soundcard levels for a good contrast. Do not
overdrive your soundcard! Get the background
noise and the transmit trace well defined and
separate. Keep in mind, how your waterfall looks
does not impact decoding, but it is harder to work
it if you can’t see it.
- Use UPPER CASE characters sparingly. Lower
case text in PSK31 varicode transmits fewer bits
of data, thus you'll increase transmit speed and
improve the likelihood of proper decoding on the
other end. For example, the difference of a
lowercase e and an uppercase E is five times
more bits! (e=11 vs. E=1101101101)
- Enable your RF Attenuation and increase the
volume. This helps keep a strong signal from
wiping out the weaker ones. Attenuation will
probably be around 20 dB, but by dropping the
noise level, the signal readability improves. AGC
(auto gain control) does nothing for a weak
signal; it only levels the louder ones.
- Use your digital modes software, or a program
like Spectrogram, to see what you noise level is
with the radio off. This will give you an idea of
how 'clean' your soundcard is. Typically,
onboard (built-in) sound hardware (as found in
most 'mainstream' computers like Dell or HP)
does not have a signal-to-noise ratio as good as
an inexpensive (less than $50) separate
soundcard. When purchasing a soundcard, look
for something with over 100 signal-to-noise ratio
in the specifications.
- Consider dual monitors (most modern video
cards have two jacks). This allows you to have
the waterfall or spectrum display on one screen,
and your logger, text window, etc. on the other. It
makes a huge difference in speed and ease-ofuse
when you don't have to swap between
screens or use smaller windows for your QSO.
- Keep your ALC reading during transmit to as
close to zero as possible. This will keep your
signal clean and your IMD at a good level (-20s
or better is ideal). Your power output will drop,
but there's no need to 'smoke' the transmit level.
PSK31 is about an 80% duty cycle. Even with a
full duty cycle rig, it still needs to dissipate heat!
Besides, 20 watts more makes little difference.
Output of around 50W is enough to work the
world, and your fellow CQs will appreciate the
courtesy. Also be sure your voice processor is
NOT enabling when using digital modes.
- Ask for an RSQ (readability, strength, quality)
report! When in a QSO, send just a tone and ask
for your IMD and a report on how your trace
looks. This will give you a better idea of
- There are hundreds of digital modes. To get
started or to learn more about the most common
ones, acquire ARRL’s ‘HF digital handbook’ by
Steve Ford, WB8IMY. For the technical types, be
sure to snag Roland Prosch’s (DF3LZ) ‘Technical
Handbook for Radio Monitoring’.
- Try 30 meters PSK31! It’s a robust band, offering
the best of 20M and 40M. It’s a small segment of
a no contesting band. Used only for digital
modes and CW. Be sure to operate within your
privileges. PSK31 can typically be found around
DEFINITIONS of TERMS USED:
AGC (Auto Gain Control): The ability to reduce
signal strength on-the-fly (fast or slow), giving you a
more level audio reception on stronger stations.
ALC (Auto Level Control): A voltage adjustment or
reading, indicating your TX signal levels . ALC is
designed to control voice and carrier signal levels,
not digital modes. Typically, if the ALC meter moves,
then the microphone gain is too high.
Signal-to-noise (S/N) ratio: A comparison of the
signal levels to the relative noise level. Ideally, a
perfect signal would have no noise, but realistically,
you’ll want a S/N ratio well within the tolerances of
the mode you’re using. PSK31 tolerates about a
10dB S/N ratio.
dB: Sound level, or ‘decibels’ are used to measure
the relative strength of a signal.
Digital Mode: A converted signal transmitted from
your radio to be ‘de-converted’ by the receiving
station. Much like a computer modem, a digital feed
is converted to analog, sent across a transmission
medium, then reconverted back to a readable signal
at the receiving station.
Duty cycle: The total time of actual transmission
levels. When your radio is transmitting, there’s an
on/off process that takes place. Transmitting at a
100% duty-cycle indicates that your are using 100%
of your radio’s power, 100% of the time. Better
radios will allow this, while others will eventually fail
under the pressure of such a load.
IMD (Intermodulation Distortion): The ratio, in dB,
used to determine the quality of your transmission.
Unwanted ‘products’ or signals reduces IMD levels.
More power does not mean better copy!
Overdrive: Turning the volume of your radio up so
high that you risk damage to the soundcard, or cause
signal ‘splatter’. Similar to maintaining your ALC
Pass band: The range that your transceiver can
receive when on a single frequency. Typically
around 3000Hz wide.
PSK (Phase Shift Keying): A form of modulation
that shifts the transmit signal in order to carry more
information. PSK31: is a digital mode created in the
1990’s by Peter Martinez (G3PLX) that is about 31Hz
wide on your waterfall.
RF (Radio Frequency) Attenuation: A suppression
of signals received. You’ll often see a noise level
reduction, with a minor sacrifice to the desired signal
reception. Check your radio’s manual on how to
RSQ (Readability, Strength, Quality): Much like the
familiar ’RST’ reports, using a 599-type reporting
scheme. Instead of ‘Tone’ (Morse Code), use
’Quality’. 95%+ readable, with a very strong waterfall
trace, and a clean (no splatter) signal would warrant
a 599 report.
Soundcard: A piece of hardware in your computer
that produces sound, and often allows input, as with
VFO (Variable Frequency Oscillator): It’s that knob
you use to change frequencies on your radio.
Varicode: A streamlined coding system that allows
nearly whatever your computer keyboard can type to
be transmitted in shorter lengths.
Waterfall: A visual display of radio signals (and other
sounds) found on the tuned frequency.
RELATED WEB LINKS:
ARRL’s ’HF Digital Handbook’,
by Steve Ford, WB8IMY
‘Technical Handbook for Radio Monitoring I’,
Roland Prosch’s (DF3LZ)
Digital Master 780, by Simon Brown, HB9DRV
Spectrogram and other software:
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