[TowerTalk] Fwd: Inductor Design and Voltage Breakdown

[Jim Lux]

On 7/31/15 1:53 PM, Richard (Rick) Karlquist wrote:
> On 7/31/2015 11:35 AM, Steve Hunt wrote:
>> Jim,
>>
>> This one may be of interest:
>> http://hamwaves.com/antennas/inductance.html
>>
>> It's the most accurate I've found. To quote the web page:
>>
>> Steve G3TXQ/
>>
>
> I have done a lot of calculations with this app and
> the results are almost always within a few percent of
> Wheeler's formula for inductance.  This is not saying
> anything bad about the web site; simply that Wheeler's
> formula isn't broken and doesn't really need fixing.
> The calculations for Q seem somewhat questionable,
> despite the high falutin' talk on the web site.
> It seems to say that Medhurst's formula for Q is too
> pessimistic.  I've never seen a coil with a Q
> exceeding Medhurst's formula.
>
> Medhurst also has a formula for self resonant frequency.
> Again, the hamwaves calculator basically validates
> this formula.  The SRF depends on whether one end of
> the coil is grounded or not, so it is application
> dependent.
>
> BTW, there is a graph in Reference Data For
> Radio Engineers showing predicted Q of coils.  This
> graph follows Medhurst's formula, without any attribution
> as to where it came from.  EXCEPT, that there is an
> error on the graph.  Where it says "diameter in inches"
> you should instead use "radius in centimeters".
> Apparently even the publishers are not aware of this
> error since it occurs in many editions of the handbook.
>
> If you need a "calculator" for inductors, you can
> program Wheeler's and Medhurst's formulas into Excel
> in 5 minutes.  Medhurst's Q and SRF formulas are most readily
> accessible in the Radiotron Designer's handbook.
>

http://home.earthlink.net/~jimlux/hv/wheeler.htm
http://home.earthlink.net/~jimlux/hv/medhurst.htm

For breakdown voltages
http://home.earthlink.net/~jimlux/hv/paschen.htm