Re: November 2018 Hawaii Ultralight DXpedition-- 15 Page Article
Gary DeBock is correct that several years ago I did try a number of approaches to a broadband FSL. Andrew Ikin of Wellbrook Communications got involved too, suggesting that a FLG100LN module might possibly work when using the FSL coil as input and the output going to the Wellbrook's DC interface box, and finally the output of the interface to the receiver. I recall that Seattle DXer Chuck Hutton gave some useful tips and ideas too on the concept of a broadband FSL.
This FSL-FLG100LN setup let me hear the then-active Papeete, Tahiti outlet on 738 kHz from my inland Puyallup QTH. The reception was poorer than with a small delta Flag at home, though. Despite my initial enthusiasm about this, a later, more detailed trial run at coastal Yachats, Oregon showed the broadband FSL was a dismal performer compared to a small Flag antenna.
More recently, Andrew Ikin kindly provided me with a custom FLG100LN module that has a 72:1 ratio impedance transformer for additional broadband FSL experiments. This is a FAR higher impedance transformation than a stock FLG100LN. We had hoped that a better match to the large FSL coil might give better results than we had in 2012. The results were the same--very poor sensitivity that bordered on worthless!
It seems that "broadband FSL" is an oxymoron, as the FSL's secret is the same as any other inductively coupled loop--it's a high gain, highly selective & resonant circuit. Bypassing this "single frequency at a time" tuned antenna (by removing the variable cap) totally defeats the antenna's purpose and benefit.
It isn't that hard to use a coupling coil around a FSL antenna and impedance-match it to give a reasonable signal to a 50-ohms input of a receiver (SDR or otherwise). However, it is still "one frequency at a time", the old fashioned way of capturing DX :^) This page has a number of approaches to coupling coils: http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm (Scroll down to the Inductive Coupling section to read about different coupling coil designs).