coils: wound vs dipped

[Phil Hobbs]

I duplicated a miniature bird telemetry transmitter from an existing design,
and would like to replace the 2 wound coils in my next one with available
dipped through hole, or even surface mount inductors

The coils are:

12 turns #36 wire 1/8"dia. (this has a 22pf capacitor in parallel in the
design with the antenna wire on one end)

4 turns #32 wire 1/8" dia.

Is this enough information that someone can give me the values I need to
order as replacements?

Thanks
Jim

If they're air core, it's pretty easy: To an accuracy of about 1%, the
inductance in microhenries of an air-core coil is given by the formula:

L = a**2 n**2
-----------
9*a + 10*b

where

a is the radius of the coil in inches
b is the length of the coil in inches
n is the number of turns.

Note that it's easy to get the turns count too low by 1/2 or 1 turn: a
hairpin counts as 1 turn. Also this formula works best for coils with
many turns.

Cheers,

Phil Hobbs

 

[Phil Hobbs]

O.K., sounds easy enough. Is the "radius of the coil in inches", the
outside radius or inside? These were wound on 1/8" drills, so I guess I
need to measure the ouside with calipers??

So the wire diameter doesn't figure in? Curious.

Jim

There are formulas that include the wire diameter, but it doesn't matter
very much--the inductance of a single wire goes as the negative
logarithm of the wire diameter, which is a pretty slow dependence.

I'd use the mean diameter (average of ID and OD) but it doesn't matter
too much at the accuracy level we're talking about, assuming the wire is
thin. Also note that this formula works only for single-layer coils.
There are formulas for multi-layer coils, but they're much more
complicated. If you have multiple layers, your best bet is to use a
grid-dip meter.

Cheers,

Phil Hobbs

 

[ian field]

There are formulas that include the wire diameter, but it doesn't matter
very much--the inductance of a single wire goes as the negative logarithm
of the wire diameter, which is a pretty slow dependence.

I'd use the mean diameter (average of ID and OD) but it doesn't matter too
much at the accuracy level we're talking about, assuming the wire is thin.
Also note that this formula works only for single-layer coils. There are
formulas for multi-layer coils, but they're much more complicated. If you
have multiple layers, your best bet is to use a grid-dip meter.

Cheers,

Phil Hobbs

GDO's are rare & expensive these days - if the OP doesn't already have one
the only realistic option might be build one!

There are several schematics in the Heath folder at the BAMA boat anchor
site, including tube, tunnel diode & transistor designs.

The twin gang air spaced tuning caps are getting scarce too! Watch out for a
70's tabletop transistor portable to salvage one from.

 

[ian field]

I dunno...I bought one off Ebay for about $25 just lately. There are pots
of them.

Cheers,

Phil Hobbs

Err - forgot all about ebay!

 

[Phil Hobbs]

GDO's are rare & expensive these days - if the OP doesn't already have one
the only realistic option might be build one!

There are several schematics in the Heath folder at the BAMA boat anchor
site, including tube, tunnel diode & transistor designs.

The twin gang air spaced tuning caps are getting scarce too! Watch out for a
70's tabletop transistor portable to salvage one from.

I dunno...I bought one off Ebay for about $25 just lately. There are
pots of them.

Cheers,

Phil Hobbs

 

[Michael A. Terrell]

If you have multiple layers, your best bet is to use a
grid-dip meter.

I used to put a known capacitance across a coil and connect it to a
signal generator through a 1 K resistor. I would tune the generator to
find the resonant frequency, and use a simple formula to determine the
inductance. This worked for single or multiple layer and any type of
core.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Homer J Simpson]

Err - forgot all about ebay!

They also trade on Heath lists.

 

[HKJ]

The coils are:

12 turns #36 wire 1/8"dia. (this has a 22pf capacitor in parallel in the
design with the antenna wire on one end)

4 turns #32 wire 1/8" dia.

Is this enough information that someone can give me the values I need to
order as replacements?

Use this program to find the value of the coil:
http://www.miscel.dk/MiscEl/miscelAirCoil.html

 

[Jim]

I duplicated a miniature bird telemetry transmitter from an existing design,
and would like to replace the 2 wound coils in my next one with available
dipped through hole, or even surface mount inductors

The coils are:

12 turns #36 wire 1/8"dia. (this has a 22pf capacitor in parallel in the
design with the antenna wire on one end)

4 turns #32 wire 1/8" dia.

Is this enough information that someone can give me the values I need to
order as replacements?

Thanks
Jim

 

[Jim]

O.K., sounds easy enough. Is the "radius of the coil in inches", the
outside radius or inside? These were wound on 1/8" drills, so I guess I
need to measure the ouside with calipers??

So the wire diameter doesn't figure in? Curious.

Jim

 

[JoeBloe]

I duplicated a miniature bird telemetry transmitter from an existing design,
and would like to replace the 2 wound coils in my next one with available
dipped through hole, or even surface mount inductors

The coils are:

12 turns #36 wire 1/8"dia. (this has a 22pf capacitor in parallel in the
design with the antenna wire on one end)

4 turns #32 wire 1/8" dia.

Is this enough information that someone can give me the values I need to
order as replacements?

Thanks
Jim

No. The missing information revolves around the ferrous core
material properties of the "coil" you are replacing. It's perm specs
and its mass are important factors. You also would need to analyse
the coil, and you need to know what frequency it is being utilized at
as well to do so.

Why do you need to "replace" them? Are you attempting to
miniaturize the circuit or such?

 

[JoeBloe]

O.K., sounds easy enough. Is the "radius of the coil in inches", the
outside radius or inside? These were wound on 1/8" drills, so I guess I
need to measure the ouside with calipers??

So the wire diameter doesn't figure in? Curious.

Jim

Two things. STOP top posting and set you computer's date and time
correctly.