Re: ferrite mini coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Neil Richardson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <neil-at-opticalrealities-dot-com>
> 
> It would be more difficult to do the math if you were using a Ferrite Rod,
> unless you knew exactly what type it was. Apart from that - they definatly
> improve performance. I used one in my mini coil, and the performance is
> awesome! I'd guess with a ferrite core, for the same performance, you can
> use a lot less than 1000 turns. Just use as many turns as you can get still,
> just to be sure :)
> 
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: 19 January 2002 19:40
> To: tesla-at-pupman-dot-com
> Subject: ferrite mini coil
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <PeterCGMN-at-aol-dot-com>
> 
>     While I was scrapping an old radio for entertainment I found a ferrite
> rod about 1/2" wide and about 4 1/2" long. Since I have read about the
> advantages about having ferrite in the center of the secondary, I have
> decided to build a small coil around it. I have two questions:

	Before contemplating any use of a ferrite rod I recommend a
flux-density calculation for the expected operating voltage and
frequency.  I'd be very much worried about saturation losses and total
failure.  About 20 years ago I tried using a ferrite slug to tune the
loading coil for a VLF band transmitter, and had serious problems with
saturation at 181 kHz with a voltage of only 1000 across the coil, which
had about 3 mH inductance. This coil had a cylinderical core about 5/8"
diameter.  I suspect that with your transistor radio antenna rod the
diameter and area are much smaller, again leading to problems.

Ed