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