[Lowfer] FSL antenna

[wa3tts at verizon.net]

Zack & All:  I recall a youtube video from a west coast LF/LF listener showing his FSL antenna in a demo with a Sony receiver 2010  with and without coupling

https://www.youtube.com/watch?v=ctRqnCVZrTg

I have a Sony 2001 with somewhat similar performance, I'm guessing his improvement on the NDB station is 30 dB or so.

I see a similar similar enhancement with a well built 17 inch diameter Litz wire loop a 1.1mh total inductance with some switched
inductance and capacitance along with a 365pf variable for tuning.

This video below shows my litz wire loop hearing Euro 1 on 183 kHz.  Although I do not do the coupled versus uncoupled demonstration in the video below, from experience
I would say the Litz wire loop also shows about a 30dB improvement coupled vs uncoupled to my Zenith or Sony radios.

https://www.youtube.com/watch?v=zwk57zWIaOQ


By the way, the Zenith 780 and 790 radios have fairly hefty ferrite bar antennas in them about an inch tall, several inches long, and 1/8" or so thick.  I can hear LF broadcasters
on these Zenith radios without the Litz wire loop when the conditions are enhanced somewhat.  

If a couple hundred dollars worth of ferrite rod materials were to fall from the sky I might play with an FSL.  But Litz wire, some capacitors and a fiberglass form are more affordable.

John E. Post (PhD in EE)  KA5GSQ's excellent article  "Optimizing Magnetically Coupled Loop Antennas" in the Jan/Feb 2015 issue of QEX is well worth absorbing.   The crux
of his article is that the optimum mutual inductance for the coupled magnetic antennas is equal to the geometric mean of the inductances of the larger loop antenna and smaller ferrite antenna ( in a radio), divided by the quality factors of the loop antenna and ferrite antenna.
I have tried direct coupling of my 17" Litz wire loop with a pair of FT50- toriod transformers to step down from about 2K ohms to 50 ohms. Seems like there is 3-4 dB loss in that arrangement but it
works OK.  If I put 1mw in at 137 kHz (Mini VNA)  in my basement rec room, my EWEs in the back yard 100 some feet away can detect the signal in the 2200m WSPR waterfall....

73 Mike wa3tts




-----Original Message-----
From: Zack Widup <w9sz.zack at gmail.com>
To: Discussion of the Lowfer (US, European, &amp, UK) and MedFer bands <lowfer at mailman.qth.net>
Sent: Sun, Jan 30, 2022 12:57 pm
Subject: [Lowfer] FSL antenna

There was a recent discussion on an AM BCB DX'ing list about the Ferrite
Sleeve Loop (FSL) antenna. These are compact antennas made with a number of
ferrite rods arranged in a 5 or 7 inch diameter cylinder around a piece of
PVC pipe or some such, with a loop wound around them. I haven't been able
to find much technical info on their construction. They seem to be mainly
used in the AM broadcast band, and people are reporting better performance
than with a 4 foot square loop.

I am wondering if any of you have used one of these, how well they perform
in the Lowfer bands, and if anyone knows of a website with construction
details.

73, Zack W9SZ

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