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It will likely be some time, if ever, before
sound cards will fully replace TNC's for MARS Data System (MDS)
operation. Bear in mind that TNC’s for PACTOR and AMTOR ARQ are still
needed for the NAVMARCORMARS MDS System. Used TNC's are often obtainable at reasonable
prices, and you can also check with the State 'Twelve' for the availability of MARS
equipment. So, take advantage of all the functionality of
your sound card, but please do not let what we offer here deter you from
becoming a fully capable MARS digital station. |
(Click Here to download
this page in Adobe PDF format)
SOUND
CARD BASICS
for MARS
Stations
THE USE OF SOUND CARD MODES IS EXPANDING RAPIDLY
THROUGHOUT NAVMARCORMARS. THESE MODES ARE PROVING TO BE EFFICIENT IN MESSAGE
HANDLING AND INEXPENSIVE TO OPERATE, ELIMINATING THE NEED FOR AN EXPENSIVE
MULTI-MODE TERMINAL NODE CONTROLLER (TNC).
If you want to get involved in sound card digital radio, you've come to the right place (at least one of them). Trust me; it's not nearly as complicated as it sounds. Here how to get started quickly and easily. If you have a computer with a sound card and an extra ten bucks or so, you're ready to go.
For sound card modes your computer’s sound card performs as a
modem for transmitting and receiving digital data. Audio output from your transceiver, is sent it to your
computer soundcard where it is processed to a readable format. Output data from your computer’s
keyboard (and/or files) is processed by the computer and sent as audio from
your sound card’s speaker jack to the MIC input of your transmitter.
To accomplish this you will need an
interface between your radio (transceiver) and your computer’s sound card. The function of the interface is to
take received speaker audio from the radio to the sound card Line-IN jack (or
MIC if no Line-In jack is available), and then take audio from the sound card
Line Out (or speaker) to the radio’s microphone circuits. In addition you will need a means to
key the radio either manually or incorporated within the interface.
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NO ELABORATE INTERFACE IS NEEDED for receive only. To just receive, you'll need a shielded audio cable with the appropriate ends, to take your received audio from your transceiver to the sound card to the computer 'line-in' or 'mic' jack.
Just
set things up in a manner that suits your particular situation. For
example;
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Sound card interface units can be built
inexpensively or purchased as kits or assembled units.
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Below
is a simple circuit that I have used (with manual PTT) for all soundcard
modes and with various rigs. A 1:1 audio transformer, as mentioned
above, is recommended for each line to avoid ground loops and possible damage
from DC current.
A simple PTT circuit such as shown
below will allow the software to key your transceiver.
There are many approaches to interfacing your radio
and computer. Here are a couple of excellent sites that cover the
interface subject if you want to build your own interface. A web search will yield many more
ideas and circuit sources, and don’t forget to check your digital software
help files for interface information. http://www.qsl.net/wm2u/interface.html
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Many will find the convenience offered by commercial interface
units beneficial. Currently there
many units available in kit and assembled versions and can be located in
Amateur radio publications or on the internet. Remember to keep it simple, and you do not need to spend
lots to obtain excellent results.
My particular set up cost just a few dollars and has worked flawlessly
for several years on all sound-card modes.
Sound-Card Digital Modes:
Listed
here are but a few of the sound card modes, concentrating on the ones of
possible interest to the MARS operator.
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MODE |
DESCRIPTION |
ADD'NL INFO LINKS |
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FEC |
Although, Although we transmit EEI
messages by voice during ECOM exercises, in an actual event digital
transmission is much more efficient and accurate. Prior to sound card
technology, an expensive modem was required to decode received AMTOR FEC. Now
your computer's sound card can do the job. If your computer does not
have a sound card, you can add one at little cost. Ask around, and someone
will likely have an extra one that you can have, and even a new card is very
cheap. Virtually any sound card will work. You don't need the
latest/greatest super-duper game card. To be safe though, if you're
buying one, check to see that it is "Sound Blaster 16 compatible". Currently
there is not, to my knowledge, any sound card software supporting AMTOR
ARQ and you are encouraged to procure a TNC for MDS operation of
AMTOR ARQ. |
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MT63 |
MT63 is a
DSP based advanced HF mode for Amateur Radio, intended to provide high
performance keyboard - to - keyboard operation on HF bands under poor
conditions. MT63 utilizes a number of revolutionary ideas, and is technically
very complex. MT63 is no more difficult to operate than RTTY, and is easy to
tune. It also provides much better performance on HF than most other
modes. MT-63 is now the standard
mode used for transmission of SCD (Single Channel Data) net traffic in MT-63 operation far exceeds
AMTOR in both speed and accuracy, especially under adverse conditions. |
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ALE |
Automatic Link Establishment
is being utilized more in MARS operation with the introduction of MARS-ALE. The primary purpose of ALE is to provide a much more reliable means for one station to call another station via HF radio. MARS-Ale soundcard software further expands ALE as a messaging tool. |
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SSTV |
Slow Scan TV is the
transmission of still images via RF.
While not commonly used in MARS it could be, and has been, a valuable
mode to transmit disaster pictures via radio. |
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PACTOR FEC |
Pactor ARQ is used in the MARS MDS/BBS system. Pactor FEC would be suitable for broadcast mode traffic transmission, but generally on MARS nets AMTOR FEC or MT-63 is used instead. Currently I know of no software supporting Pactor ARQ. At one time Brian Beezley, K6STI, offered a DOS based sound card program called 'RITTY' which reportedly would do Pactor ARQ. RITTY required a TRUE Sound Blaster sound card and, I am told, would NOT run on the vast majority of sound card clones. I am not sure that it is still supported, and the last license fee I heard was around the cost of a good used TNC. |
also see NTP-8 (c) p.960 |
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PSK31 (BPSK and QPSK) |
PSK31 is the mode that really sparked a general interest in sound card communication modes. PSK31 is based on an idea by SP9VRC and developed by Peter Martinez, G3PLX, who also developed AMTOR. Based on RTTY, PSK is used for live keyboard-to-keyboard QSOs at 50 WPM (31 Baud) and uses "Phase Shift Keying" to signal mark and space values, instead of changing the frequency like RTTY (FSK). PSK31 operates in a very narrow bandwidth allowing several individual, non-interfering, QSOs to simultaneously occupy one 3000 Hz bandwidth allocation. PSK31 is very effective with low power and QPSK improves communication under some adverse band conditions. For MARS purposes, these features are offset by PSK31 being relatively slow, and having no real forward error correction (FEC) features. In addition to BPSK and QPSK there are several variations to PSK31, but are beyond the scope of this article. |
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MFSK |
MFSK is a technique for transmitting digital data using multiple tones, extending the RTTY two tone technique to many tones, usually, but not always, one tone at a time. MFSK has several performance advantages:
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Software and Where to Find it:
Clicking on
the program name will take you to the download site. From time to time
you may not be able to link to these sites as they are
sometimes moved, removed or whatever. If you have
any trouble just email NNN0GAATen for a copy via email or CD.
Click on Program Name to
download:
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Mode > |
F/S/C |
Amtor FEC |
Pactor FEC |
PSK31 |
MFSK |
MT-63 |
Hell-
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Packet |
RTTY |
Q15x25 |
SSTV |
Throb |
CW |
Fax |
TNC Term-inal |
Other
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MixW (a) |
S |
Y |
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TrueTTY (b) |
S |
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F=Freeware, S=Shareware,
C=Commercial
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(a) http://www.mixw.net/ |
Other Sound Card Software Sources
(Check these sites often as new programs and updates occur frequently)
Tuning your sound Card
Setting Audio Levels:
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Adjust the sound card audio INPUT level such that a
nominal signal tuned in on the transceiver will be seen prominently in the
program signal display window without overdriving the sound card input. (See
the MT-63 Screen Shot below for an example of how this might look.)
Note that other windows
applications which you run on your PC that provide sound card adjustment
controls may change your settings! You may have to re-adjust these levels.
Adjust your radio MIC gain
level for normal SSB operation. Turn off all speech processing. Adjust
the sound card audio Playback Master Volume and Wave levels to the
transceiver such that a small amount of ALC voltage is detected at the transceiver
while transmitting into a proper antenna load (50 ohms), then back down until
there is no ALC
action at all on
your transceiver meter. (The
Master Volume is the course control and the Wave control is the fine
adjustment.) Several of the software packages help
files have good detailed instructions on sound card tuning. There are
many approaches to this, as you will see. Settings should be checked with each different mode and
saved for later retrieval with QuickMix. Soundcard output may vary with frequency. Generally the highest output levels
will be at lower frequencies, so make your adjustments on the lowest
frequency you plan to use to prevent over driving on higher bands. The lower output on higher
frequencies will still be adequate with these modes. |
