[IRCA] Original 3" Bar FSL Tecsun PL-380 Model-- Shielded Litz Wire Question

[d1028gary@xxxxxxxxxxx]

For those who have access to the scarce 100mm x 20mm x 3mm ferrite bars and who have built (or plan to build) the original 3" Bar FSL Tecsun PL-380 model (for which the construction article is posted at http://www.mediafire.com/view/w0gcek56f6aq7kr/3_Inch_FSL_Tecsun_PL.doc Â), the question has arisen about whether the shielded Litz wire procedure used in the new 4.25" FSLÂ"Pest Control" PL-380 model (posted at http://www.mediafire.com/view/je2v6xorlnjmmbo/4.25inchFSLPL-380.doc Â) would be a good idea to improve nulling performance. At first this seemed like a routine conversion, and two of the original 3" Bar FSL PL-380 models were modified here to include shielded Litz wire. 
 
As it turns out, the question of adding shielded Litz wire to this original 3" Bar FSL model is a little more complicated. This model was designed to include a Bar FSL which is pretty close to the maximum RF tolerance level of the PL-380's Si4734 DSP chip. As long as the article's instructions are carefully followed there is no problem with DSP chip overloading, but any changes which increase the sensitivity of the model run the risk of borderline DSP chip overloading. 
 
The conversion to a shielded Litz wire system has the net effect of increasing the RF signal level from the 3" Bar FSL, mainly because none of the RF signal is lost along the extended run of Litz wire. As such the sensitivity level of the model is slightly increased, triggering borderline DSP chip overloading in the two test models here (on the X-band frequencies from 1600-1700 kHz). The 4.25" Bar FSL has no such issue, and avoids any DSP chip overloading even with the shielded Litz wire system. 
 
As designed, the 3" Bar FSL model already has exceptional nulling ability for a portableÂ(even without the shielded Litz wire system ), and my recommendation for those who have the 100mm ferrite bars is to construct the model according to the original article, and avoid the shielded Litz wire system. I'm fairly certain that anyone who builds the model according to the instructions will be more than satisfied withÂits DXing performance. 
 
73 and Good DX, 
Gary DeBock (in Puyallup, WA, USA) 
 
 
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