Motorola MICOM-2TS Dokumentacja Pobierz pdf (Strona 84)

Automatic Link Establishment (ALE)

The MICOM-2E unit incorporates Automatic Link Establishment (ALE) to

select the best working channel from the channels programmed into the

unit automatically without user intervention. The ALE incorporates all

advanced data transmission techniques required by MIL-STD-188/141A

and FED-STD-1045. The ALE feature thus ensures the user of the best

possible link without requiring prior knowledge of radio communications.

Previously, HF radio operations had to be familiar with the constantly

varying nature of the ionosphere, the atmospheric layer that reflects HF

radio waves back to earth. A knowledge of the ionizing effects of

sunspots, the seasons, time of day, and fluctuations in the earth’s

magnetic field was essential for the operator to find the best frequency

for any particular link.

Manufacturers of HF-SSB equipment tried numerous methods to assist

the operator in this difficult task. For example, various squelch circuits

are employed to overcome operator fatigue from interference noise.

Another aid is the use of several receivers so that the operator does not

have to search continuously for incoming calls. More advanced are

scanning receivers combining selective calling.

A more recent approach has been adopted to combine scanning with a

“handshake” to establish a link. However, because the first link is not

always the best, some manufacturers use Link Quality Analysis (LQA),

which measures a few propagation parameters, such as the bit error

rate (BER) and S/N. If the result is below a desired threshold, the

search continues until a reasonable link is found. Here again, there is no

guarantee that a better channel was not overlooked. Motorola’s ALE, a

technological breakthrough in HF-SSB communication, combines

scanning, selective calling, sounding, channel selection, and LQA.

These features, all automatic, ensure that even with an unskilled

operator, communication takes place on the channel with the best link

quality.

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Motorola MICOM-2TS Dokumentacja Strona 84