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ALE Area

 

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Welcome to the ALE Area of Tactical Link Systems

Note that in this area, ALE is NOT a beverage. In this context, it means
 "Automatic Link Establishment".

The "ALE Info" area will be hosting information on Automatic Link Establishment, equipment field trials, and related activity, while the "ALE Chat" area is for web-based discussions on the use of FED-Std 1045 and Mil-Std 188/141 linking protocol along with a question and answer format that will allow users of this mode to exchange meaningful and timely discussion.

If you would like to hear what ALE signaling sounds like,
click here:      

(this sound file is courtesy of Leif Dehio)

Speaking of other sounds heard on HF,
here is a link that I recently ran across:
<http://det.bi.ehu.es/~jtpjatae/sound.html>

A fully-documented ALE handbook is available online
at: <http://www.its.bldrdoc.gov/pub/oa-rpt/hf-ale/handbook/>

Past and predicted solar flux numbers are available at: <ftp://ftp.ngdc.noaa.gov/STP/IONOSPHERE/INDICES/indices.txt>

The terrestrial, 10.7 cm forecast, covering the next
27 days, is also available at:
<gopher://gopher.sel.noaa.gov/00/weekly/27DO.txt>

Downloadable (and free) HF radio channel prediction software
is available at: <http://elbert.its.bldrdoc.gov/hf.html>

The "WUN Club" has an excellent write up on their webpage that covers
the ALE protocol in some detail.

 

An excellent book is available which covers the subject of ALE:

"Advanced High-Frequency Radio Communications"
Authors: Eric E. Johnson, Robert I. Desourdis, Jr.
Greg D. Earle, Stephen C. Cook, and
Jens C. Ostergaard
ISBN: 0890068151

 

 

 

Publisher: Artech House, Boston/London Price: $109.00
(hey, limited interest reference books happen to be expensive)
I purchased this book from Amazon about two years ago.

Search via the ISBN number and this book will come up at
amazon.com

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The basics of ALE will also be covered below:

 

ALE Basics

For those who perhaps have heard the term "ALE", or heard ALE signaling on the air, Below will be a very short overview of the purpose of ALE and why it exists:

The primary purpose of ALE is to provide a much more reliable means for one station to call another station via HF radio.

Prior to ALE, operators of HF radio equipment needed to develop a body of skills that would allow them to know as accurately as possible, what specific frequency segment of the HF radio spectrum could be used at a particular time of day, time of year, and period of the current sunspot cycle, in order to reliably raise another specific radio station in which they need contact. Making the right decision wasn't always easy.

The results would be that a pre-arranged set of specific radio channels may be defined and each station would call the other on each of the frequencies until they were able to hook up with one another. Not a very robust or efficient system, but simplicity can work, given enough time.

The next iteration of operations would have been that each station could monitor all the assigned frequencies simultaneously, through the use of separate equipment, or would have channel scan capability to scan channels in order to listen for a call directed to them. Again, not very efficient.

ALE places all these decision-making requirements inside of the radio itself.

As the power of computing and microprocessors have advanced with time, MITRE Corporation took the lead in developing a standard method of allowing the radios themselves to manage their channel-selecting decisions when the operator needed to call another station.

Below are the key points of how ALE functions. Keep in mind that the decisions that the radios make, will tend to mirror how a real person would normally have to manage the operations of frequency selection, exchanging signal reports, keeping records of which channel is best, and so forth.  So... Here Goes:

(NOTE, This section is under construction:)

                

 

REQUIREMENTS FOR ALE TO WORK:

bulletChannel Assignments:
bulletA group of specific channels are assigned to a group of stations that
wish to communicate with one another. Time of day, time of year, and position in time, along the 11-year sunspot cycle will determine what
the "BEST" radio channel frequency will be for any two stations to communicate.

The number of channels and spacing between the assigned channels
are planned such that no matter what time of day, time of year, or
position on the 11-year sunspot cycle, one or more channels will be located in this "best" area of the HF radio spectrum, between
1.6 and 30 MHz.
bulletNet Members:
bulletAll members that will be participating in a "NET" (Network) will have
an assigned Alphanumeric ID, as a net member. These ID's can be up to 15 characters in length. Currently under the ALE protocol, any specific NET can have a maximum of 16 net members.

If the planned net will have more than 16 members, then additional nets
will have to be created.
bulletNet configuration can be based on the distance the stations are from
one another. An example is that a sub-group of stations that all need to
to communicate with a common station that is some distance away,
may want a special group of net channel frequencies that will more
likely support the geographic distance between the subgroup of
stations and the primary one that is some distance away. 

bulletAll radios in the net will have all net members listed in a look-up table
in a specific order. This will be explained later, but revolves around the
the need to be able to make a "NET-Call", and all members of the called
net will respond back to the calling station during a specifically-defined time slot. Defined time-slots will limit the possibility of two or more
called stations trying to acknowledge (ACK) the calling station at the same time.

 

bulletCallsigns:
bulletEach station has it's own "Self-Address" which identifies it's
station to other net members.
bulletEach NET has a "NET Address". Net addresses are used for
"NET Calls" where a station wants to call, and communicate
with, all stations assigned to the net.
bullet"ANY Calls" are a type of call where the calling station wants to
make contact with any station on the frequency which has
an ALE address, whether the called station is a member of
the assigned net, or not. The calling station does not have to
have the called station's ALE address in their membership
list.
bulletEquipment requirements:
bulletAll radios will have either broad-band antennas that will not have to
be retuned when changing channels, OR will use high-speed, automatic antenna couplers.
bulletAntenna tune time should be within only a few seconds. Network parameters require that the station in the net with the longest antenna tune-time must have that tune-time defined in the radios of all other members of the net. This allows a calling station to wait a specific length of time for a response from the called station, and the wait time will include the maximum-defined antenna tune period.

 

ALE In Operation:

bulletGiven the above requirements, the following overview can be
given, showing the basis of the ALE protocol:

 

bulletRULE #1: All stations on the net, not actually in use, will be scanning
assigned net channels, looking for calls from other stations or
monitoring for sounding messages.

Sounding messages allow stations to keep a log of all stations in the
net and to store info on signal quality. Signal quality measurements
include:
bulletBit Error Rate (BER)
bulletSINAD (Signal+Noise+Distortion/Noise+Distortion)
bulletChannel Multipath measurements

 

bulletRULE #2:  When a station is not linked, sounding messages can be
sent either manually, or at predetermined intervals of:
bullet30 minutes
bullet60 minutes
bullet90 minutes
bullet120 minutes

Normal practice is to have stations automatically sounding when not
linked to another station. The "Sounding Interval" or "Sounding Rate"
is chosen in order to balance the frequency of soundings with
channel occupancy. More stations in the net, with a greater
sounding frequency, will occupy the net channels with a larger percentage of sounding messages. 

 

bulletRULE #3: All stations, whether linked or unlinked status, always have
their ALE modems monitoring the frequency that the radio is currently
tuned. This allows the radio, whether actively engaged in a conversation
or not, to decode sounding messages.

 

bullet 

To be continued...."

 

 

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Last modified: August 17, 2009