[Drake] Roofing Filters

[dmartin]

Been doing some reading lately on the concept of roofing filters and their 
influence on near-in blocking dynamic range, etc., performance. The TT Orion 
seems to be the first factory offering to take advantage of a variety of 
various bandwidth front end roofing filters. Of course, Rob has long offered 
his Sherwood 600 Hz roofing filter option for the 4C. Tom Rauch, W8JI, has a 
great article in the current WorldRadio where he gets into receiver 
performance concepts. He pretty much disses the stock R-4C on close-in 
performance and concludes that a Sherwood 600 Hz roofing filter makes the 4C 
acceptable, at best, on CW performance. However, my confusion over 
the "acceptable on CW" is this: if you check the performance tables on Tom's 
website at http://www.w8ji.com/receiver_tests.htm, you'll note that although 
the close-in performance of the stock 4C is as poor as several references 
state, the "R-4C heavy mod" specs at least equal to >exponentially exceed< 
anything else tested, including the Icom 7800 and current Orion. Along with 
the addition of Sherwood's 600 Hz however, the "R-4C heavy mod" 
includes "solid state double balanced high level mixers". I'm quickly aware 
only of Rob's IC third mixer mod. Anyone know any details on the 1st and 2nd 
mixer mods on Tom's test 4C?

Not considering such mods, mind you, just want to better understand how such 
apparently superior performance, equal to and exceeding $3,000-$10,000 
radios, could have been squeezed out of what began life as a 4C? From this I 
would conclude that an otherwise stock 4C but with Rob's 600 Hz roofing 
filter and possibly his 3rd mixer mod might make for a CW receiver very 
competitive with anything currently offered today, no?

Dan
WB4GRA 

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