Microbit RRC-1258 MkII(s) Manual de usuario descargar pdf (Pagina 17)

90

Computers in Amateur Radio

I’ve shown an IQ polar diagram

in Fig 7.3a-c. Here the I axis repre-

sents a change in amplitude of the

carrier wave, whilst the Q axis shows

any change in the carrier’s phase. If

we start with amplitude modulation,

the only part of the vector that

changes is the magnitude along the

I axis and this changes in response

to the modulating signal. Let’s now

move on to look at what happens

with simple phase modulation,

where a 180 degree shift is used to

convey a digital signal. In this case

the vector amplitude remains

constant but the vector will flip

between 0 and 180 degrees in

response to the modulating signal.

Frequency modulation can also be

demonstrated and the vector will

remain the same length but will

rotate clockwise to show an LF shift

and anti-clockwise for an HF shift.

If we take control of the I and

Q values we can adjust the values to

generate amplitude, frequency or

phase modulation with comparative

ease (see Fig 7.4). In addition to

these relatively simple modulation

systems, by manipulating the IQ

data we can generate a range of

complex modulation systems that

employ both amplitude and phase

modulation that would be very

difficult to implement with traditional

hardware. Using IQ data the genera-

tion of simple or complex modula-

tion schemes can be completed

entirely in software, which brings

tremendous flexibility. The resultant

baseband IQ signal can then be

applied to an IQ up-converter to

produce the final operating fre-

quency. The up-converter is a

relatively simple device that mixes

the IQ data with a pair of local

Fig 7.3:

(a) IQ data for an

amplitude

modulated

signal,

(b) IQ data for a

phase

modulated

signal,

(c) IQ data for a

frequency

modulated

signal.

Fig 7.4: Using IQ

values to control

vector position.

© RSGB

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