Re: FSL Antenna Tuning Course Video

Gary DeBock

On Wed, May 27, 2020 at 07:53 PM, Max Italy wrote:

I noticed that passive coupling of a 20" air loop antenna with capactitor to a DSP radio gives better signal than removing the internal ferrite and wiring it directly. Although the DSP chip has an automatic tuning circuit.

This makes me think that the automatic tuning is not so accurate and it may be the main reason why hard wiring a FSL is not even considered an option?

However I did the test with a cheap radio.

Hi Max,

Actually there have been quite a few FSL's hard wired into DSP-chip Ultralight radios, and some of them work quite well. Most of the attempts have been with the Tecsun PL-380, which seems to tolerate an FSL's powerful RF output as long as a small coil is used (3" or less diameter). 

I've attached a construction file for the hard wired 3 inch FSL Tecsun PL-380, of which about 10 were made by me and other DXers back in 2016. A couple of 2 inch FSL Tecsun PL-380's were also made, one of which I sent to Hiroyuki Okamura in Japan. These hard wired FSL experiments were attempted with the CC Skywave Ultralight, but their Si4735 DSP chips were fried pretty quickly. A PL-380's Si4734 DSP chip was also fried when a larger (5 inch) FSL was hard wired in place of the loopstick. 

The hard wired 3" and 2" FSL Tecsun PL-380's work quite well, but the main drawback is that they require the very rare Russian surplus 100mm x 20mm x 3mm ferrite bars, which haven't been available commercially since 2012. These are the same lightweight ferrite bars used in the 5 inch "Frequent Flyer" FSL antennas, so the demand for these rare ferrite bars is extreme.

73, Gary DeBock (in Puyallup, WA, USA)

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