Sure, Jeffrey -  I also have no precise idea what the insertion loss of the two series filters is, but they cleaned up my 15 and 12-meter issues.  Some rough-and-ready tests with an Elecraft XG-3 Signal Source and HDSDR's S-meter suggest it's a few dB, and more than made up by the 11-dB Norton preamp.

I am confident that a high-quality set of band-pass filters would be preferable, but since I'm trying to skim 8 bands simultaneously, that would be pretty clumsy to implement - imagine an 8-way splitter, 8 filters, an 8-way combiner and an amplifier to make up for the losses.  Actually, that's what W3LPL uses at his station, as described on the RBN blog recently - reversebeacon.blogspot.com

73, Pete N4ZR
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The partial schematic shows what is in the front end between the SMA connector and the A/D converter.  He even removed some components that should be there for optimal performance. There is definitely no filter.

I modified one of my Perseus radios to have a similar unfiltered input.  I carried it will me all over the US, Canada, and Israel to give lectures on SDR. I took a simple signal generator with me to show that the untuned SDR radio would receive very well up to almost 500MHz and demonstrated how alternating Nyquist bands would change tuning direction.

Perhaps you might find limited performance with the purchased external filters. That would come as a result of the reflections of the signals and the noise from the A/D sample and hold being reflected back by the filters into the A/D input. To maximize performance one would need to buy or build what are called non-reflective (aka absorptive) filters for your specific bands of interest.

73,

Jeffrey Pawlan  WA6KBL

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