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AE5ME > ARES 29.03.16 04:57l 24 Lines 6032 Bytes #999 (0) @ WW
BID : 7COGGLZD1FOW
Read: GUEST
Subj: Digital Emergency Communications Series by AD5XJ (
Path: IW8PGT<IV3ONZ<IZ3LSV<IV3SCP<IW0QNL<JH4XSY<JE7YGF<7M3TJZ<HG8LXL<N0KFQ<
AE5ME
Sent: 160329/0209Z 34480@AE5ME.#NEOK.OK.USA.NOAM BPQ1.4.64
Mode Symbol Rate Typing Speed Bandwidth Olivia 8-250 31.25 baud 1.46 cps (14.6 wpm) 250 Hz Olivia 8-500 62.5 baud 2.92 cps (29.2 wpm) 500 Hz Olivia 16-500 31.25 baud 1.95 cps (19.5 wpm) 500 Hz Olivia 32-1000 31.25 baud 2.44 cps (24.4 wpm) 1000 Hz
You will notice the actual symbol rate is not intuitive. That is to say that the throughput speed does not go up proportionately with bandwidth. In fact the most efficient throughout is using the 8 tones / 500 Hz submode. Precisely the reason it is used on the SATERN Digital Net each Saturday.
What is intuitive is that the wider modes with more tones have in increase in noise tolerance. In other words, the 32 tones / 1000 Hz sub-mode is quite robust, but half the speed of 8 tones / 500 Hz sub-mode.
MFSK From the FLDIGI documentation…:
MFSK16 and MFSK8 are multi-frequency shift keyed (MFSK) modes with low symbol rate. A single carrier of constant amplitude is stepped (between 16 or 32 tone frequencies respectively) in a constant phase manner. As a result, no unwanted sidebands are generated, and no special amplifier linearity requirements are necessary. The tones selected are set by the transmitted (4 or 5 bit) bit pattern and a gray-code table.
The mode has full-time Forward Error Correction, so it is very robust. Tuning must be very accurate, and the software will not tolerate differences between transmit and receive frequency. The mode was designed for long path HF DX, and due to its great sensitivity is one of the best for long distance QSOs and skeds. MFSK8 has improved sensitivity, but is very difficult to tune, and suffers more from Doppler. It is useful as the band fades out.
MFSK-32 and MFSK-64 are high baud rate and wide bandwidth modes designed for use on VHF and UHF. These are very useful for send large documents or files when some transmission errors are can be tolerated.
This is an example of properly tuned MFSK16 signal with a s/n of approximately 9 dB.
[Author note: We have seen considerable success with the MFSK-64L (long leader) mode on the SATERN So. Terr. Digital Net on HF. It is fairly quick and has some robust qualities.]
MFSK Picture Mode
Fldigi can send and receive small images using all MFSK baud rates. When operating with other modem programs you should limit sending pictures to the MFSK-16 baud rate. The program can send and receive MFSK images in both black and white and in 24 bit color. The transmission mode for MFSKpic is similar to FAX.
Reception of an MFSKpic transmission is fully automatic. The MFSKpic transmission has a preamble sent which will be visible on the text screen. The preamble reads as "Pic:WWWxHHH;" or "Pic:WWWxHHHC;" for b/w or color respectively. The WWW and HHH are numbers specifying the width and height of the picture in pixels.
The successful reception of a MFSKpic is highly dependent on s/n conditions. The data is transmitted as an FM modulated signal and is subject to burst and phase noise on the transmission path. It can provide excellent photo transmission on a really good path.
Use of this mode to send images should be limited to very small pictures (smaller than 150 X 150) due to the slow throughput of bit intensive data and the length of transmission.
MT-63 The FLDIGI documentation describes this mode this way:
MT63 is an Orthogonal Frequency Division Multiplexed [OFDM] mode consisting of 64 parallel carriers each carrying part of the transmitted signal. The tones are differential BPSK modulated. MT63 employs a unique highly redundant Forward Error Correction system which contributes to it robustness in the face of interference and facing. The tones have synchronous symbols, and are raised cosine modulated [to limit spurious sideband generation]. This mode requires a very linear transmitter. Over-driving leads to excessive bandwidth and poorer reception.
The mode is very tolerant of tuning and FLDIGI will handle as much as 100 Hz of mis-tuning. This is very important since MT63 is often used in very low Signal to Noise ratios. There are three standard modes:
Mode Symbol Rate Typing Speed Bandwidth MT63-500 5.0 baud 5.0 cps (50 wpm) 500 Hz MT63-1000 10.0 baud 10.0 cps (100 wpm) 1000 Hz MT63-2000 20 baud 20.0 cps (200 wpm) 2000 Hz
In addition there are two interleave options (short and long) which can be set on the MT63 configuration tab. The default calling mode is MT63-1000. If the short interleave is used then one can expect some compromise in robustness. The long interleave results in somewhat excessive latency (delay between overs) for keyboard chatting. MT63-1000 with the long interleave has a latency of 12.8 seconds.
You can change from receive to transmit immediately upon seeing the other stations signal disappear from the waterfall. You do not need to wait until the receive text completes. Any remaining data in the interleaver will be flushed and the associated receive text printed quickly to the Rx pane. Tx will commence right after the buffer is flushed.
MT63 may be operated in the default fixed audio frequency mode. In this mode you are not allowed to randomly place of the signal on the waterfall. Your transmit signal, and also the received signal should be centered at 750 Hz for MT63-500, 1000 Hz for MT63-1000, and 1500 Hz for MT63-2000.
The downside to this mode is the need for an extremely flat audio passband in the receiver for the mode bandwidth. The accuracy of the received data suffers where the audio passband has the characteristic “humpö in the mid-frequencies of the received audio. Also, since the data is spread over a broader spectrum, the net resulting carrier power average is some 25% of other AFSK modes.
The graph above depicts the very broad and linear use of the transmitted spectrum. The total average power spectrum is a fraction of other modes. Where you may see a 50 watt signal from PSK, MT-63 would possibly be only 10 watts or less. This does not make it less capable, just less efficient. It also shows the almost perfect audio passband linearity of the station transmitter.
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