[Drake] Roofing Filters

[Thomas Beltran]

Dan -

I have two R-4Cs, one with all the Sherwood mods (including the replacement
power supply board and the capacitor board), and the other, stock.  I think
the modded receiver is much better, and way more quiet.  Here are Rob
Sherwood's comparisons:  http://www.sherweng.com/table.html   Another site
with comparisons, is the Elecraft website - http://www.elecraft.com/, which
uses the ARRL data, but is useful in that it culls that data from many QSTs
and puts it all together on one page.  The Sherwood roofing filter kits
include both CW and SSB.

>  Anyone know any details on the 1st and 2nd
> mixer mods on Tom's test 4C?

I have corresponded with a ham in Austraila, I think, that sent me a pdf
schematic of the double-balanced mixers.  I'll try to find it and send it to
you.  However, after finishing the Sherwood mods, I was quite happy with my
radio, particularly in comparison with my Mark V, and stopped there (as I
recall, it was not a high parts-count circuit).  But then I am a casual
operator, and even a stock R-4C would do fine in most situations for me.

> 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?


>From my review, I can't really tell - all of these comparisons are
incomplete, and I wouldn't envy the job of trying to keep them up to date.
Moreover, the different sites use different comparision language (at least
to me with a non-technical background).  An accurate comparison that I would
like to see would be W8JI's heavy and medium modded radios, with one having
all the Sherwood mods.   But I'm not sure if Sherwood's, "dynamic range
narrow spaced" - 2khz., is that same as W8JI's "2khz IMDR."  If they are the
same, then on the chart at http://www.w8ji.com/receiver%20IM3%20sorted.htm,
Sherwood (with 84 db 2 khz dynamic range) would come in just a bit lower
than Tom's modded Mark V, but above the 7800!  And, perhaps the Mark V, with
the roofing filter, would move up a bit.  I guess I personally would be most
interested in Tom's medium modded Drake, rather than completely reworking
the radio.

One example of the difficulty in keeping up, is the Inrad Roofing filter for
the FT-1000MP.  If it does make a significant difference, it would seem
almost silly to continue to use the stock figures (or at least not include
the new figures), when the mod only costs $ 150.00.  I've had the roofing
filter in my Mark V for over a month, and I notice that at least my radio
sounds much cleaner, and I cannot tell anymore when local hams get on 17
meters unless I actually tune them in.   In my opinion, the Mark V still
does not compare with my Drake on CW.    Tom W6EIJ