- Stub (electronics)
In electronic signaling, a stub is a section of
transmission line with a calculated length. It is used forimpedance matching or to obtain an exactcapacitance orinductance .Because stubs take on reactive properties as a function of their
electrical length , stubs are most common inUHF ormicrowave circuits where the line lengths are more manageable. Stubs are often used for antenna matching.Smith chart s can also be used to determine what length line to use to obtain a desired reactance.hort circuited stubs
The general equation for the input impedance of a short circuited line is ::where j is the
imaginary unit , is thecharacteristic impedance of the line, β is thephase constant of the line, and "l" is the physical length of the line.Thus, depending on whether is positive or negative, the stub will be inductive or capacitive, respectively.
The Length of a stub to act as a capacitor is then given by:
::
The Length of a stub to act as an inductor is given by:
::
Open circuited stubs
For an open circuit, the general equation for input impedance is ::where j is the
imaginary unit , is thecharacteristic impedance of the line, β is thephase constant of the line, and "l" is the physical length of the line.It follows that whether is positive or negative, the stub will be capacitive or inductive, respectively.
The length of an open circuit stub to act as an Inductor:
::
The length of an open circuit stub to act as a capacitor:
::
Computer network stub
Electrical length = (Rise time) * (Speed of light) * (Cable propagation relative to light speed)
Maximum stub length = Electrical length * (1/6) [cite web|title=Application Bulletin AB-6 RS-485 Systems--Making Them Work|url=http://www.nve.com/Downloads/ab6.pdf 071115 nve.com]
This is relates to buses like SCSI, RS485, CAN-bus, Ethernet etc..
References
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