Analog-to-Digital Conversion is an electronic process in which a continuously variable signal (analog) is changed, without altering its essential content, into a multi-level (digital) signal.
The input to an analog-to-digital converter (ADC) consists of a voltage that varies among a theoretically infinite number of values. Examples are sine waves, the waveforms representing human speech, and the signals from a conventional television camera. The output of the ADC, in contrast, has defined levels or states. The number of states is almost always a power of two — that is, 2, 4, 8, 16, etc. The simplest digital signals have only two states, and are called binary. All whole numbers can be represented in binary form as strings of ones and zeros.
Digital signals propagate more efficiently than analog signals, largely because digital impulses, which are well-defined and orderly, are easier for electronic circuits to distinguish from noise, which is chaotic. This is the chief advantage of digital modes in communications. Computers “talk” and “think” in terms of binary digital data; while a microprocesor can analyze analog data, it must be converted into digital form for the computer to make sense of it.
A 8 bits ADC means it can get 2 ^ 8 states (256) at the digital state. If the ADC can accept a voltage between 0 to 5V, a 0 digital value will be for 0V and 255 for 5V. Any voltage between 0V – 5V will be converted in a digital value from 0 to 255 (256 states)
Most antenna rotors include a Potentiometer (POT) that is connected with the antenna mast axis. So when the external rotor turns, the POT resistance is also moving. If this POT is powered @ 5V, it will provide a Voltage feedback, and this V. feedback will be in relationship with the antenna position. Example for an antenna that works from 0? to 360? and powered @ 5V:
- V for 0? (CCW limit or Left)
- 1V for 72?
- 2.5V for 180? (middle range)
- 5V for 360? (CW Limit or Right)
When a 8 bits ADC is working with an Azimuth Antenna (as previous example = 360?) we’ll asign a voltage for each position. As there is 256 states, we’ll get the following resolution:
Resolution 8 bits ADC for 360?? = Total rotation anglee / ( 2 ^ 8 ) = 360? / 256 = 1.4062?
It means every 1.4? will get a different digital value.
Analog Value?? Digital Value
0.00?? ??????? 0
1.40?? ??????? 1
2.80?? ??????? 2
4.20?? ??????? 3
If we are working with an Elevation Rotor, we’ll make the calibration from 0? to 90?. So, the same 8 bits ADC will provide x4 better resolution.
Resolution 8 bits ADC for 90?? = Total rotation anglee / (2 ^ 8 ) = 90? / 256 = 0.3515?
Similar for 10 bits ADC, this ADC will provide 2 ^ 10 states = 1024 states
Working with a Azimuth Rotor (360?):
Resolution 10 bits ADC for 360?? = Total rotation anglee / (2 ^ 10) = 360? / 1024 = 0.3515?
|ADC||Azimuth Resolution 360?||Elevation Resolution 90?|
|8 Bits||360 / 256 = 1.4?||90 / 256 =? 0.3515?|
|10 Bits||360 / 1024 = 0.3515?||90 / 1024 = 0.0878?|
|12 Bits||360 / 4096 = 0.0878?||90 / 4096 = 0.0219?|
[jbox color=”yellow”] Note:
The ARS-USB uses an internal 10 bits ADC.[/jbox]
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