With regard to nulling ability, I wonder if the optimum length-vs-diameter ratio for FSLs is different than for standard (solid, non-hollow) ferrite rod antennas. In the early days of the UltralightDX Yahoo Group there was some experimentation with very skinny, long ferrite antennas. In fact, group co-founder John Bryant created an unusually skinny antenna composed of six or seven 1/2" X 7.5" Amidon rods in a row. The rods were cleverly compressed "on-axis" to simulate a single long rod for RF receiving purposes (did you ever know John *not* to be the King of Clever in any of his projects? :^)
Around the same time I also experimented with the nulling ability of ferrite rod antennas using a 3/4" X 18" commercial Stormwise ferrite rod. I'm sure Gary must have tried various length-to-diameter ratios, too. The diminutive Sony SRF-T615 receiver was presumed to have excellent nulling due to its skinny (albeit small) antenna; we were just trying replicate or improve upon the length-vs-diameter ratio of our antennas in larger sizes for better sensitivity.
Now with this talk about the benefits of "stubby" Ferrite Sleeve Loop antennas, it makes me wonder if the preferred ratio works in the opposite direction if the ferrite is a hollow cylinder? Gary, can you chime in with your thoughts here?
---In ultralightdx@..., <nhp@...> wrote :
Your observation of superior nulling ability with the stubby FSL antenna is very interesting Gary. One of the most intriguing aspects of the old SRF-59 in my recollection was that in spite of its tiny size, it had very good nulling capability.
Is it a rule of thumb that a stubby antenna has better nulling capabilities? (though a single rod hasn't much signal pickup overall)