Hi,
I'm looking for articles on how the new roofing filter designs work. I've seen the PowerPoint on Rob Sherwood's site, but it doesn't answer all my questions. Questions came up in a discussion with a friend of mine who is considering the INRAD roofing filter mod for his Kenwood TS-950SDX. He operates almost 100% CW, and doesn't hear any IMD products. His beef is noise from stations that are just outside the passband of his cascaded IF crystal filters. He's hoping the roofing filter will increase the selectivity of the radio. My sense is that it will help, but not by providing additional selectivity. My understanding is that it will improve the dynamic range within the passband by keeping the hardware AGC in the downstream IF stages from being triggered by loud adjacent signals. Is this the correct way to think about it? My friend maintains that the roofing filter would provide selectivity as well, but my sense is that unless it's narrower and/or has steeper skirts than the IF filters, it won't. I believe the Kenwood roofing filter mod is only on the order of 2K-3K wide, so the selectivity shouldn't improve. Even if the roofing filter was the same or narrower than his IF filters, would it improve selectivity? Is there an analogy with cascaded IF crystals? Typically, a filter in the final IF stage (e.g., in the 450KHz range) outperforms a filter in an earlier stage (e.g in the 8 MHz range.) Is this because it's easier to make better filters at lower frequencies, or because it's more effective to filter after any amplification by previous IF stages? Obviously, I don't know squat about this. 73, Dick WC1M _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
