Hard-Wired FSL Antennas-- How Big is Too Big?

Gary DeBock

For those interested, the first signs of some limitation in the PL-380's Si4734 DSP chip's ability to handle powerful RF inputs from a hard-wired FSL have appeared.
In a step-by-step approach to test this out, the 3" Bar FSL composed of 8 Russian surplus 100mm x 20mm x 3mm ferrite bars (the construction article PL-380 version) was thoroughly proof-tested in this aspect, and had superb performance from 521-1700 kHz. A similar experiment with the same size of  3" FSL hard-wired into a CC Skywave had excellent performance on the frequencies up to about 1400 kHz, but showed erratic operation on the X-band frequencies (1600-1700 kHz). This erratic reception sounded similar to signal flutter, with the choppy-sounding signal dropping in and out several times a second. As such, I do not recommend any transplant of the 3" bar FSL into a CC Skywave model.
Tonight's experiment was to transplant a 3.25", 10-bar FSL into a PL-380. As with the CC Skywave, the low band performance was excellent, but the X-band frequencies had the same choppy-sounding reception as the CC Skywave did with the 3" FSL. Side-by-side comparisons of a 3" FSL PL-380 (the article version) and this new 3.25" FSL PL-380 on the X-band showed the former to be clearly superior, with no issue in the reception or nulling of any station up to 1700 kHz.
For experimenters with access to these Russian surplus 100mm ferrite bars, it is not recommended to hard-wire FSL's composed of more than 9 bars into a PL-380. I know that Steve R. has made a 9-bar FSL model, and he reported good reception across the band.
73 and Good DX,
Gary DeBock (in Puyallup, WA, USA)

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