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AE5ME > ARES 27.03.16 05:48l 8 Lines 2630 Bytes #999 (0) @ WW
BID : 3KFYED6SJOGU
Read: GUEST
Subj: Digital Emergency Communication Series by AD5XJ (SATE
Path: IW8PGT<IZ3LSV<I0OJJ<GB7CIP<N0KFQ<AE5ME
Sent: 160327/0317Z 34290@AE5ME.#NEOK.OK.USA.NOAM BPQ1.4.64
Recent software and hardware entries into ham radio allow computer interfacing with hardware that contains not only the radio interface components, but often a self-contained soundcard that functions independently of the computer. Products like the Tigertronics SignalLink, RigBlaster Advantage, and Timewave Navigator take advantage of this configuration to off-load the analog-to-digital sound conversion process to the internal soundcard of the product, and thus relieving the computer of this task. These products also incorporate a VOX PTT for transmit keying without having to have a separate PTT line.
While not necessary, having a separate soundcard for this dedicated, specialized purpose considerably enhances the quality of the audio conversion process while reducing the amount of work the computer is required to do. Computers with a second external soundcard or sound interface may be used to accomplish the same thing with some additional interconnection to the computer interface for the radio. Error Correction
When digital signals are transmitted, the electrical signals of the digital information are used to modulate the amateur transmitter. When received, band conditions and signal strength become a factor in how accurately that information is received. The pulses of the digital information may be lost or interrupted by noise, precipitation crashes, fading, or other types of interference. Loss of data results in errors in the decoded digital data.
Many software methods have been employed to correct for this loss of data and restore the received data to the original content. The modern use of techniques like Forward Error Correction (FEC), longitudinal compression, Trelles Coding, encoding with Viterbi, NRZI or other encode schemes, may be used alone, or in combination, to attempt the error correction of data received and make the digital mode more robust.
These are sophisticated mathematical calculations that require considerable computer power. Not all digital mode software use all these methods on amateur radio digital modes. For instance PSK31 uses a Varicode character encoding to reduce the overall amount of data that has to be sent. But no errorcorrection is employed, so when noise or interference causes data loss, the result is text that is essentially garbage.
The opposite case is the OLIVIA digital mode. Sending data at about the same speed, but considerably more robust and employing heavy error correction, OLIVIA can decode digital signals when its' tones cannot even be discerned from the audio.
Next time we will take a look at digital modes and make some comparisons.
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