Re: Simpler spur fix

Hans Summers


Be careful using SMD inductors in Low Pass Filters: they may have trouble handling the required power, and the lower Q may affect the filter characteristics. 

Also be careful using SMD inductors in Band Pass Filters and Low Pass Filters because they will more easily saturate, this will limit the dynamic range and IP3 of the receiver. The lower Q will also increase the insertion loss of some Band Pass Filter designs.

SMD inductors may also lack the inherent self-shielding properties of the toroidal inductor shape. 

This page is a very educational study on what size toroids are necessary to avoid them becoming the limiting factor for dynamic range and IP3. But you need a very good mixer otherwise the mixer is already limiting the performance.  
In the uBITX the dynamic range and IP3 are already limited elsewhere so the type of inductor used is not likely to be a limiting factor. 

SMD or pre-wound axial inductors make things easy. But toroids make things high performance. Everything being a trade-off as usual. 

73 Hans G0UPL

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