All In Flashcards
(53 cards)
Expand ALE
Automatic Link Establishment
What is the purpose of an ALE system?
To provide a reliable, rapid, method of calling and connecting during constantly changing ionospheric conditions, reception interference and congested channels
What does a standalone radio combine?
A HF Radio combines an HF SSB transceiver with an internal microprocessor and MFSK Modem
What does the HF SSB transceiver do when the system is not actively in contact with another station?
Scans through a lift of HF frequencies called channels
Expand and describe BER
Bit Error rate/ratio
Measures signal quality
bits:errors
How does an ALE system contact/reach a specific station?
Caller enters ALE address,
Controller selects best available idle channel,
then sends a brief selective call
Describe the operation of selective calling
Only let’s in signals who have the correct digital code
How is an ALE link confirmed by 2 communicating stations?
Visual alert and Audible alarm
list 4 common applications provided by ALE
Voice HF Internet connectivity for email SMS file transfer real time chat via HF text
How does an ALE system typically signal the operator that a HF frequency optimised for both sides of the communications link has been established
Audibly and visually at both ends of the link
What was ALE originally developed for?
The alleviation of the need for the radio operator to constantly monitor and change the radio frequency manually to compensate for ionospheric conditions or interference
List 5 common users of ALE network systems?
Emergency disaster relief agencies,
military,
guard forces
List 3 organisations known to use ALE for emergency management and disaster relief
Red Cross,
NATO,
US Armed forces
Define Asynchronous systems?
These systems require extra elements added to the transmitted data stream to inform the receive terminal where a word begins and ends
Define Synchronous systems
These systems require extra elements added to the transmitted data stream to inform the receive terminal where a block of data begins and ends
in an asynchronous system what portion of the start bit activates the receive terminal clock?
Leading edge of start bit
once an asynchronous system is running, from where does the receiving terminal take its timing source from?
centre of the bit
How often is an asynchronous systems clocked re-synced?
OK completion of each frame
Determine the overhead of an asynchronous system who’s complete frame consists of 1 start bit, 19 data bits and 2 stop bits
3/22=
3 (start and stop bits)/22 (total number of bits)
Why are asynchronous systems generally limited to a maximum amount of data they are able to send between start and stop bits?
Timing error. The larger the block of data transmitted the larger the timing error
What percentage of overhead does an asynchronous system generally employ?
20%
State 2 methods that a synchronous system may utilise in order to achieve timing synchronisation between transmit and receive terminals?
Provide separate clock between the lines of the tx and RX terminals,
embed clocking information in the transmitted data signal
in a character bit oriented synchronous system what 3 elements make up the total frame structure?
SYN/ Control Character/ Data
What additional synchronisation allows the receive terminal of a synchronous system to determine the beginning and end of a frame of data?
Pre and Post amble
