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TOPICS: · Receiving AMTOR |
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. SOME REGIONS AND STATES HAVE ESTABLISHED
NETS FOR EXPERIMENTATION WITH THESE MODES.
CHNAVMARCORMARS BCST 08-03 -
SOUND CARD FREQUENCIES
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.
(Click Here to
download this page in Adobe PDF format)
This information should be considered un-official. To review the current official position of NAVMARCORMARS regarding sound card modes refer to the following Chief MARS Broadcasts:
Also see: NAVMARCORMARS WEB PAGE ON SOUND CARDS for other official sound card info.
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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. |
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Although, since this was first written, Alabama has changed to MT63 as the standard method of transmitting general messages, Amtor is still a viable mode for Alabama nets, and is used to send traffic on regional nets. The nature of many general messages makes voice transmission very difficult to copy and to understand so you will find digital reception very beneficial. Actually once the hardware is set up to receive Amtor you can also receive MT63, and vice versa. 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. 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".
NO ELABORATE INTERFACE IS NEEDED to receive AMTOR, or to send it, for that matter. To 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;
I've had QSO’s with stations that had no interface at all! They just put their computer microphone in the vicinity of the radio speaker and feed the audio to the sound card acoustically. It is not the best set-up, but I've tried it myself and it really does work! That is all that's needed to receive. For transmit setup, go to the interface topic. Software for AMTOR You'll need some software.
Currently I know of only three Windows based programs that decode AMTOR. Two,
TruTTY and MixW, are shareware and one, MultiPSK, is freeware.
Clicking on the program name above will take you to the download
site. From time to time |
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That's it! You can now receive AMTOR FEC!
How's that for a bargain? Transmitting AMTOR FEC is almost as easy. All you need now is a connection from your sound card ‘Line Out’ to your transmitter. This can be accomplished in several ways with little effort and expense. See the INTERFACE section for details…….just remember KEEP IT SIMPLE! Don't forget, the MARS preferred AMTOR operating method is with a TNC for full FEC and ARQ capability. See Important Note. That's it! You can now receive AMTOR FEC! |
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 |
In NAVMARCORPMARS, AMTOR FEC is used to transmit all general messages, such as Chief MARS Broadcasts and Info Broadcasts, to our Region and State nets. In addition FEC is also used to send traffic between stations equipped to operate in this mode. Currently there is not, to my knowledge, any sound card software supporting AMTOR ARQ and you are encouraged to procure a TNC for Full MARS support of AMTOR FEC and ARQ |
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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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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. Keep an eye on this one. It appears to have great potential for MARS operation. |
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Packet |
Packet radio is a digital
method of communications adapted from a standard computer protocol (X.25) by
which computers communicate with each other. The version adopted for
NAVMARCORPMARS use is AX.25. Packet radio was originally developed for VHF
use, but has since been modified for HF . |
http://www.packetradio.com/primer.htm |
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Q15X25 |
Q15X25 is a 15 tone packet
mode with a Kiss/AX25 interface, and from its performance, should long ago
have replaced conventional packet for HF use! Q15X25 is now available for
Motorola EVM, LINUX PC and Windows PC sound card operation. 'BEACONS USING Q15X25 ARE ENCOURAGED. THIS
MODE MIGHT BE ADAPTABLE FOR THE MDS BUT WE NEED MORE EXPERIMENTATION UNDER
DIFFERING PROPAGATION CONDITIONS.' |
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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 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. Again, I encourage you to
procure a TNC for full MARS digital capability |
also see NTP-8 (c) p.960 |
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SSTV |
Slow Scan TV is the transmission of still images via RF |
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ALE |
Automatic Link Establishment The primary purpose of ALE is to provide a much more reliable means for one station to call another station via HF radio. |
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Interface Basics: I don't know, …..maybe it's the ads for some commercial sound card interfaces that lead people to believe that this is a complicated process. It isn't. You need to take audio from the transceiver to the sound card (to receive) and from the sound card to the transceiver's microphone circuits (to transmit), and you'll need some method to key the transceiver. I have used this circuit with various rigs
with all the programs and all modes mentioned here with Here are a couple of excellent sites that cover the interface subject if you want to build your own interface. http://www.qsl.net/wm2u/interface.html
If you'd prefer, kits with full PTT circuitry are available for around $25 and assembled units are available for around $50 from this and other sources. http://www.packetradio.com/ Many find the convenience offered by commercial interface units beneficial. Currently there many units available 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 digital modes. |
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 |
ALE |
TNC Terminal |
Other
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MixW (a) |
S |
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TrueTTY (b) |
S |
Y |
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F=Freeware, S=Shareware, C=Commercial
(a) http://www.mixw.net/
(b) http://www.dxsoft.com/
Other Sound Card Software Sources
(Check these sites often as new programs and updates occur frequently)
Here is a little utility program that is a 'must have'. QuickMix is a freeware and can be downloaded clicking here.
Tuning your sound Card
Setting Audio Levels:
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Adjust the sound card audio OUTPUT level 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) with the MIC Gain control at a nominal setting. After this adjustment, you can reduce the MIC gain control slightly to achieve full output power with no ALC deflection. Note that full output on a 100 watt transceiver would be about 100 watts if using a single tone (CW) from the sound card, but would be about 50 watts if using the double tones of a PSK31 carrier. Turn your speech processor OFF. When you get your first PSK31 contact, ask
the other station for an "IMD report" on your signal. (You must
allow several seconds of "no text" for the reading to be made.) A
properly adjusted audio input level to your transceiver will have an IMD at
least -20 dB below the carrier and a very clean signal will be around -28 dB.
It should be noted that a strongly received PSK31 signal (S9 or greater) can
appear to have a high IMD level when viewed on the digi program display. This
is often the fault of the receiver's front-end being over driven by the
strong signal. Before issuing a bad IMD report to another station, you should
add attenuation to the receiver and observe the reading under a nominal
signal strength. 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, but just remember that once you have
found settings that work for you they should work with any of the programs.
Here's a little utility program that's a "MUST HAVE"! It allows you to store and retrieve your sound card settings, avoiding the process of readjusting each time another program changes them. QuickMix is freeware and can be downloaded from here. |
by NNN0GAA
for Alabama (experimental) Digital Net use.
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DIGITAL NET PROCEDURES 1. NECOS <XMTR
ON> 2. MEMBERS CHECK IN <XMTR
ON> 2a ACKNOWLEDGE STATIONS CHECKED IN <XMTR
ON> 3. PASS TRAFFIC <XMTR
ON> <XMTR ON>
<XMTR ON>
<XMTR ON>
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