[Prev][Next][Index][Thread]
Secondary Frequency(fwd)
----------
From: Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent: Tuesday, August 18, 1998 7:50 PM
To: Tesla List
Subject: Re: Secondary Frequency(fwd)
Tesla List wrote:
>
> ----------
> From: RWB355-at-aol-dot-com [SMTP:RWB355-at-aol-dot-com]
> Sent: Tuesday, August 18, 1998 12:31 AM
> To: fwd
> Subject: Secondary Frequency(fwd)
>
> Hi to All,
>
> Below are two given coils.
> What is the frequency of each coil? Another coiler and I disagree on the
> resonant frequency of these two coils. Can somebody help?
>
> Coil A:
> 21.7" long
> 3" diameter
> Wound with 1230 feet AWG 28
> He says 418kHz (I say 200 kHz)
>
Should be about 410-430 kHz depending upon "closeness" of the wind.
> Coil B
> 10.84" long
> 6" diameter
> Also wound with 1230 feet AWG 28
> He says 275kHz (I say 200 kHz)
>
Should be about 275-295 kHz depending on "closeness" of the wind.
> Who is right??
>
> Thanks,
> Reinhard
It looks like your friend is right. You're taking the physical wire
length and using it to estimate the 1/4 wave response as though it were
a straight wire. This doesn't work, since winding it in a coil adds
substantial inductance as well as distributed capacitance to ground,
resulting in a self-resonant 1/4 wave frequency that's higher than that
predicted by wirelength alone.
The correct way is to compute the inductance using Wheeler's formula,
and estimate the "effective" capacitance (assuming it's mounted
vertically with the base grounded) using Medhurst's tables. Another way
is use a design aid such as Wintesla (or similar). This can be found at:
http://members.aol-dot-com/rscopper/index.htm
Safe coilin' to you!
-- Bert --