# Effect of Coiled cord on 30KHz Square wave signal??

Discussion in 'Electronic Basics' started by royalmp2001, Aug 16, 2005.

1. ### royalmp2001Guest

Can anyone tell me what effect a coiled cord, like that of a headphone
cord, would have on a 30KHz square wave signal (waveform or otherwise)?
Thanks
Marius

2. ### John PopelishGuest

Is the signal passing only one way through the coiled cable, or also
returning back through a second conductor?

3. ### BanGuest

It would have no effect if the length is in normal proportions. Otherwise it
would attenuate the signal resistivly depending on the load impedance and
the DC resistance of that cable. There wouldn't be any frequency depending
phenomena because the effect of the coil is cancelled by the return current.

4. ### royalmp2001Guest

Hello again, John...
You have answered so many of my questions in the past..thanks for
looking.

Well, the application consists of passing a 30KHz square wave signal to
an anti-static wrist-strap through its single-conductor coiled cable.
The strap is worn on one wrist with the signal passing through the
human body and then out to another wrist-strap and coiled cable which
go back to the oscillator's ground connection.
I know that the effect of the human body tends to round off the
squareness of the waveform, but I wonder what effect the coiled cables
are having. Obviously the load current is going to be quite
small...like less than 1mA.
I cannot find a source of straight-cable anti-static wriststraps.
Thanks
Marius

5. ### John PopelishGuest

At this current, the resistance of the wire is insignificant, compared
to the skin and body resistance. The only effect that may show up is
the inductance of the two coils. You can roughly approximate this
with the common formulas used to approximate the inductance of spaced,
single layer solenoidal coils. The more you space the turns, the
lower the inductance. So the worst case would be when the two cables
are not extended at all.

http://www.qsl.net/in3otd/indcalc.html

Once you have a rough idea of the coil inductance, you can use the
normal inductive impedance formula, 2*pi*f*L=ZL multiplied times the
current, to estimate the voltage drop across these coils.

6. ### mikeGuest

Obviously??? that's my favorite technical word...
Why not just figger out what parameter is interesting to you and measure
it?
mike

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