R
Reg Edwards
- Jan 1, 1970
- 0
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Gary wrote -
I never heard anyone ask this question before.
The Length of the coil is the "MEASURED LENGTH of the
windings, END TO END".
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Have you ever used a 12" ruler to measure the 'length' of a coil?
Wind a single layer solenoid on a cylindrical former about 1.5" in diameter.
Wind on exactly 10 spaced turns of 0.1" diameter wire.
This is a very common sort of coil used in HF radio transmitters.
Place the measuring rule along the surface of the coil in the direction of
the coil's axis.
Between which two points near the ends of the coil do you measure its
length?
Rotate the coil 180 degrees on its axis and you will find you can measure a
different length.
Or you can define the length of the coil as being the number of turns times
the winding pitch.
Which of these lengths do you insert in your inductance calculating program?
They can give you 3 inductance values differing by several percent.
As the number of turns decreases the differences increase.
As someone else has pointed out, when there is only one turn the answer can
be silly.
So length must be precisely defined. Furthermore the definition must apply
to any number of turns, perhaps excluding a single turn which can be a
special case. Single-turn coils are frequently used as radio antennas.
The above problems are solved in program SOLNOID3 which can be downloaded in
a few seconds from website below and run immediately. Or it can be run
without downloading.
SOLNOID3, besides inductance, calculates several other useful properties of
single layer solenoids from AF to UHF.
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Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
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