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AE5ME > ARES 29.03.16 03:56l 12 Lines 3279 Bytes #999 (0) @ WW
BID : A6GQ9ZCCEEQY
Read: GUEST
Subj: Digital Emergency Communications Series by AD5XJ (SAT
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Sent: 160329/0209Z 34475@AE5ME.#NEOK.OK.USA.NOAM BPQ1.4.64
DIGITAL COMMUNICATIONS (part 2) by AD5XJ Ken
Disclaimer: These are my comments on digital communications and are not necessarily all there is to know on the subject. As with everything computer related – there are at least six ways to do the same thing. Given this caveat, let me say this is opinion and not the complete story. I only relate to you my experience of 5 or more years using digital modes and as SATERN Digital Net Manager to give you the benefit of my experience. I will leave the rest for you to research as you see fit.
This installment is a bit lengthy. There is a lot of information here which may be overwhelming at first. However, familiarization with this material will go a long way to understanding the digital ham radio enthusiasm. Take the time to use this material to do some listening on your own. You make your own conclusions about the modes discussed.
I encourage you to experiment with the digital modes in receive to get the feel of each mode before trying to get on the air in QSO. You will learn the sounds of the transmitted signals and the methods and practices of each mode. Good etiquette for any mode is good amateur practice.
The descriptions below are a thumbnail sketch of common ham radio digital modes in use at the time of this writing. It is designed to give you a closer look at each mode and highlight the advantages and shortcomings of each.
There should be a distinction made between the digital mode and the transmission method used. As amateurs, we have AM, FM, SSB, FSK and other modulation methods to transmit voice and data information. Digital modes may use one or more of these modulation methods when transmitting. The most common method on HF is SSB/AFSK (with the upper sideband being the default on all bands) modulation although it is possible to also use FSK for some digital modes (see the discussion on RTTY). On VHF/UHF, the FM/FSK method is very common for data transmission for much higher data rates.
The digital modes that are transmitted are unique and separate from the modulation methods used to transmit them. I hope you can understand the distinction.
PSK31
This digital mode is a very narrow band Phase Shift Keying or Binary PSK (BPSK as it is more commonly known) mode for text transmission in keyboard to keyboard chat, and automated text mailbox applications. The normal bandwidth is about 60-80 Hz when adjusted to modulate your transceiver properly. The most widely used sub-mode has a character send rate is about 30-31 characters per second – hence the 31 at the end of the PSK designation. There is also a PSK63 and PSK125 sub-mode for faster symbol rates although with a much broader bandwidth of 100-200 Hz.
This popular mode attempts to send digital signals by modulating a continuous audio frequency by shifting the audio carrier in phase by 180 degrees for each transition of the digital data. Each digital data transition from 0 to 1, corresponds to a shift in phase of the audio carrier from 0 to 180 degrees in phase. This is an extremely efficient transmission method in that power is in a very small spectrum (60-80 hz) and not spread out over a much broader spectrum as is SSB speech (2.5 Khz) . Normal data communication can be
obtained with 20 watts or less of power, even QRP.
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