Re: Working with shorter (and cheaper) ferrites - The Backpack FSL
Hi Michael:toggle quoted messageShow quoted text
Thanks for your post. I have thought about it some, and I think the problem is that the coil itself would be very small. An FSL with rings of ferrite would be easy to make (no ferrite winding form is needed), and IMO would be very cool to look at! However, based on the various FSLs I have assembled and torn apart, it is the diameter of the coil of wire, not the ferrite, that is primarily responsible for grabbing the RF energy, and increasing the coil size is the primary factor in a more sensitive FSL.
Another aspect: using rings would put the ferrites, and the gaps between them, parallel to the Litz wire, rather than the wire running perpendicular to the ferrites and gaps as with bars & rods. My sense, based on a limited understanding of electromagnetic theory, is that the latter is actually preferable, although I could be wrong. Anybody know more on this???
There are materials available to check all this out, though. I see that a 100 mm (4 inch) diameter ferrite sleeve, 54 mm (2 inches) long could be assembled from six 100 mm rings from eBay seller Combat Super Store, for $44 shipped. This would lead to a Litz coil of about 4.5 to 5 inches in diameter, depending on the coil/ferrite gap you choose. There would likely be enough room for a MW coil using moderately-thick Litz wire, especially with a large-value varicap such as the 684 pF model from zlowe7. Having built a few FSLs of this size with bars and rods, the performance doesn't match up with FSLs of 8 or 10 inches in diameter, so I wouldn't think that it would be worth the cost. However, I encourage someone with $44 burning a hole in their pocket to give it a shot :-)
Bainbridge Island, WA
--- In ultralightdx@..., "Michael" <michael.setaazul@...> wrote: