RADIO HABANA CUBA
DXERS UNLIMITED
WEEKEND EDITION
SATURDAY, JULY 21, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hello, amigos! Welcome to the weekend edition of your favorite radio show...
Today you will hear a Dxers Unlimited's special report. The topic is the now almost-one-year-old NEW DIGITAL COMMUNICATIONS MODE... a keyboard-to-keyboard radio system that provides outstanding performance with low power and simple antennas... On the air it sounds like this:
[Sound bite: MFSK16 CO2KK calling CQ]
And as always at the end of the show, you will be able to listen to Arnie Coro's HF plus 6 meters propagation update and forecast...
Now let's begin with today's SPECIAL REPORT:
Ever heard about MFSK16? I think I mentioned it here at Dxers Unlimited once or twice, most recently in the March 27, 2001 mid-week edition when talking about software for the digital communications modes, when I dealt with PSK31, the digital keyboard to keyboard communications mode created by Peter Martinez G3PLX who, in a goodwill gesture to the international amateur radio community, made the software free for downloading at several world wide web sites. PSK31 is available for download right here in our Dxers Unlimited file section, too!
MFSK16 can be considered as still more efficient and robust keyboard-to keyboard-mode for amateur radio communications... Listen again to an MFSK 16 signal, just as your radio may be picking it up on the amateur radio bands.
Here we go with MFSK16, and by the way, that's CO2KK, my ham radio station calling CQ:
[sound bite: cut of CQ]
Yes, you have just heard how my amateur radio station CO2KK was calling CQ using the MFSK 16 mode.
MFSK16 is above all a DX mode, designed to communicate effectively at great distances despite severe variations strength, multi-path propagation etc. So again, I do insist that MFSK16 is a DX Mode.
Radio Teletype (RTTY) was used for many years, and some hams still use it. MFSK8, MFSK16 and MT63 are new digital keyboard-to-keyboard modes that open up a new frontier to low power amateur radio enthusiasts wanting to work DX.
The MFSK Option But what is MFSK? It 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 Overview for Beginners
MFSK has several performance advantages:
- High rejection of pulse and broadband noise due to narrow receiver bandwidth per tone
- Low baud rate for sensitivity and multi-path rejection - data bit rate higher than symbol baud rate
- Constant transmitter power
- Tolerance of ionospheric effects such as doppler, fading and multi-path
- Most important of all, with an MFSK system, the error rate improves as the number of tones is increased, so with as many as 32 tones the performance is unrivalled. With PSK systems, the opposite is true.
And above all, MFSK can be implemented at your amateur radio station or short wave listening post by simply loading a very well-written and bug-free software, building two very simple cables to interface the computer sound card with your radios, and learning how to use it!!!
In the case of the short wave listener, only one cable has to be made, the one that goes from the receiver's audio output to the computer's sound card input... In an upcoming edition of Dxers Unlimited I will be talking about the sound card interface.
Now, let's review MFSK...
Disadvantages:
Let's be fair -- there are disadvantages to MFSK! The main disadvantages are related to the narrow spacing and narrow bandwidth of the individual tone detectors -- drift can be a problem and accurate tuning is essential. Good tuning indicators and AFC are necessary at the slower speeds. It is important that the radio transceiver be very stable, and also that it has very small frequency offset between transmit and receive (preferably less than 5 Hz).
How it Works:
MFSK is a system where individual pulses of different radio frequencies carry information, and the data carried depends on the frequency of the pulse. This is the same as FSK, for example radio teletype (RTTY), but rather than two different frequencies, many more are used -- from 6 to 64, for example. MFSK16, so far the most popular version of this mode, uses 16 tones. Each tone transmitted is just like a Morse code dot, but they follow each other without pause, on slightly different frequencies.
MFSK systems generally use non-coherent detection, and space the many tones as closely as possible, to restrict the transmitted bandwidth.
The transmitted tones must be spaced at a separation equivalent to the baud rate, or a multiple of the baud rate -- the rate at which the "dots" are sent; otherwise it is difficult to separate one tone from another.
Say we are using an MFSK system with 16 tones (16FSK), operating at 15.625 baud with FEC Rate = 1/2, and an ASCII alphabet using 10 bits/character. Then:
Symbol Rate = 15.625 baudThat is, you may actually communicate at a speed of 31.25 words per minute...Channel Data Rate = 15.625 x log216 = 15.625 x 4 = 62.5 bps
User Data Rate = 62.5 x 1/2 (FEC RATE) = 31.25 bps
Text Throughput (CPS) = 31.25 / 10 CPS = 3.125 CPS
Text Throughput (WPM) = 31.25 x 60 / (10 x 6) = 31.25 WPM
This will take place in a bandwidth little more than 16 x 15.625 = 250 Hz.
So this is not a wideband mode at all, something that allows the use of narrowband receiver filtering.
PSK31 operates at 31.25 baud, and in QPSK mode gives error-corrected text at 31.25 WPM approximately. It has the narrowest bandwidth, less than 100 Hz.
In terms of performance, of the examples given, only MFSK16 and PSK31 are considered practical for DX QSOs. PSK31 often performs poorly on long path, and provides no improvement when the FEC is used, so is usually used without it.
MFSK is virtually as sensitive as PSK31 in practice and is unaffected by doppler. It is also less affected by interference, and offers effective FEC. But as I said a while ago, MFSK16 has about two and a half times the bandwidth needed by a PSK31 signal...
MFSK16
The first serious Amateur Radio MFSK modes are now in use: MFSK16 (and slower but more robust MFSK8). Using test software by Nino IZ8BLY, initial QSOs were held 18 June 2000. The first QSO was from ZL1BPU - IZ8BLY on 18.105 MHz, then ZL1AN - ZL1BPU on 3.560 MHz. During the initial tests, rates from 7.8 to 31.25 baud were tested, with from 8 to 32 tones! The MFSK16 specification proved to be the best performing compromise. MFSK8 and MFSK16 are now freely available in the STREAM software by Nino IZ8BLY.
Here's what you can expect using these modes:
On 17m, long path signals are normally weak and fading, but good hour-long contacts can be made on a regular basis, with 25W transmitter power and dipole antennas.
On 20m, conditions are much more unstable, although signals are stronger and the band open for longer. Copy is good on long path using 25W. Nets are quite feasible.
80m at night is very noisy, with very bad multi-path. Copy is close to 100% on 500mW transmitter power across town, or 10 - 25W between New Zealand and Australia (3000 km), something not generally possible with any other digital mode.
The software is being continually upgraded as a result of feedback from expert testers. These tests build up operating experience and provide feedback to software designers on how best to control and operate the MFSK16 mode.
STREAM, the MFSK16 the software by Nino IZ8BLY, is free for downloading right here in our Dxer's Unlimited files section or from the official MFSK16 website at http://www.qsl.net/zl1bpu/MFSK.
The program is very easy to install, and if need be also to uninstall. It is very well-written and very intuitive, so by following the help file, you may start listening to MFSK16 signals just a few minutes after making the receiver-to-computer connection cable.
There are not many amateur radio stations using this mode yet, so you may have to take some time to find one, but once you have started to see how MFSK16 provides perfect copy on your computer screen... the urge to build the other cable, the one that goes from the soundcard's output to the transceiver audio input will make you do it in a few minutes... See you on MFSK16 mode soon, 20 meters is the most popular band for MFSK16 users, so try monitoring 20 meters first...and remember how it sounds!!!
[Sound bite: MFSK16]
And now here is Arnie Coro's Dxers Unlimited's HF propagation update and forecast:Solar activity is low, but the number of sunspots is rather high, reaching here a WOLF number of 203, according to Angel Gonzalez Coroas the Cuban expert solar observer. Solar flux is around 145 units, and as I said here a week ago, the peak activity of this solar rotation is going to be, and it effectively is, much lower than expected... So daytime maximum useable frequencies are going to be rather low indeed, while the typical summer season pattern of much better HF propagation after local sunset is going to continue.
There is a cluster or coronal holes that are just reaching the Sun's central meridian, so next week we may see geomagnetic field disturbances related to the stream of particles coming from the coronal holes when they are in a geo-effective position. Sporadic E openings will continue to bring in 6 and 2 meter bands DX, plus TVDX and FM broadcast band distant signals...
Send your comments about the show, signal reports and QSL requests to arnie@radiohc.org. See you on 20 meters MFSK16 soon, amigos radioaficionados!!!
Arnie Coro CO2KK
Havana, Cuba
July 21, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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