Re: ferrite vs sensitivity

ferrite61 <dxrx@...>

The answer is complex, but does use a non-calculus approach. For a given inductance, The selectivity and sensitivity are both optimzed when the following conditions are met:
1.) The coil is centered on the ferrite rod
2.) The coil occupies about 40% of the ferrite rod length.
3 .) The coil has each turned spaced to a distance equal to the wire (NOT wire + insulation and/or jacket) diameter.

Therefore there is a "correct" number of turns of wire, and gauge of wire that will make a coil of the needed inductance. Using litz is tricky because the woven wire is referred to as a "bundle diameter". This is the correct diameter to use. To figure out the diameter one has to convert "circular mils"... simply take the square root of the number shown, and divide by 1000. This answer is in inches. For example 400 circular mils = 20/1000 or 0.02" diameter.

IMHO most commercial receivers use too much wire poorly centered. As others have shown, doing "an alignment" upon several coils on ferrite rods almost always improves reception with just a little adjustment of the coil and the trimmer. In the case of moving the coil towards the center, this will increase the inductance, selectivity, and sensitivity. However, the coil has too many turns to accurately center the coil, and the trimmer runs out of adjustment. I have formulas that I refer to in order to get this "right", but this might not be the time or place to go into that. /IMHO

Paul S. in CT

--- In ultralightdx@..., Richard Berler <lrdheat@...> wrote:

The sensitivity of my ICF-S5W and ICF-EX5 with their 6.375" bars is the equal of my PR-D5 with it's 8" bar. If constructed properly, should there be an expectation of greater daytime sensitivity with an 8" bar in a radio, or is it like a calculus problem where we are already approaching the limiting case with a 6.375" bar?
On another topic concerning EX5 vs S5W, I had assumed that the S5W had greater raw sensitivity. With experimentation just a few miles further away from the mw rf jungle in my area (largely related to the abundance of Nuevo Laredo mw's in addition to Laredo's stations), the two sets appear identical as far as usable sensitivity. If the S5W is more sensitive, the EX5 seems to counter with a lower noise floor. The rf jungle and relatedmixing products are so intense that (on all of my radio sets including the Grundig G3 with ssb and sync options, and the Tecsun 390 with it's 1 KHz filter) only mixing products are heard on 1230 KHz, yet 4 miles down the road, Corpus Christi is heard on that frequency in comfortably listenable fashion.

Join { to automatically receive all group messages.