On/Off Keying Flashcards
What is meant by an Element?
The element is a function of time and it’s polarity may be MARK (on or 1) or SPACE (off or 0)
Define On/Off Keying
It turns the carrier frequency on the send a positive, 1 or mark, and off to send a negative, 0 or space
What is a telegraphic structure?
It is a sequence or combination of elements to convey information.
E.g. Letters in morse
What is meant by the term baud?
Baud is a unit of telegraphic speed.
It is the number of elements transmitted in second.
If 50 elements are transmitted every second then the keying rate is 50 bands
What does ETD stand for and explain what it is
Element time duration
It’s the time taken for the duration of one element.
Normally expressed in milliseconds
What formula is used to determine the ETD?
ETD = (1000/bauds) ms
This can be converted round to work out the baud speed from the ETD e.g.
Bauds = (1000/ETD)
Make sure you don’t get seconds and milliseconds mixed up!!
What does FKF stand for? And what is it?
Fundamental Keying Frequency
Is the keying rate expressed in hertz
It is the modulating frequency for On/Off keying
How many of the signals harmonics are used to create the needed square wave?
3, the 3 first odd harmonics up to harmonic 5
Harmonics 1, 3 and 5
How is a On/Off Keyed signal easily determined on the kit?
Listening into the headphones - sounds like morse
Looking on the sonograph - looks like morse
How is are the receiving and transmitting bandwidths of a On/Off keyed signal determined?
The transmitting bandwidth is 5 times the baud speed
Receiving bandwidth is 3 times the baud speed
What is the formula for working out the FKF?
FKF = (keying rate in bauds/2) Hz
