Hmmmm........... Ed, I almost tried using the built in
"translator" in Outlook...but then I recognized some of those words, like
"is" and "the". :-() It almost let the smoke out of my head.
Seriously though, I don't understand the filter setup
technicalities. I can get through setting them up per the defaults in the
manual, but I would like to understand more about what you said. I'm not
sure why a filter would be advertised as a 250hz filter but actually have a
(usable?) bandwidth of 370hz. Is this just a difference in how it's
measured?
I have SN/0690 and am just now installing the KRX3. It arrived a few
months after the radio, back in mid to late 08, and I just never got around
to installing it. I have identical filters in both the main and sub receiver
(13khz, 6khz, 2.8 & 400 respecitively, with # 5 empty) so I can try out
diversity receive. I don't do much CW so didn't figure I needed a 250hz.
I'm sure I'll be asking some questions about this in short order,
once I get the rig back together. I am doing some of the mods and am
currently waiting on some parts and the REV C or D (or whatever it's up to
now) DSP board.
Stan Rife
W5EWA
-----Original Message-----
From: elecraft-boun...@mailman.qth.net
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Ed Muns
Roofing filters are selected by either of two ways. One is by directly
selecting FLx on the K3 front panel. The other is by changing the DSP
bandwidth via WIDTH, LO CUT or HIGH CUT. When the DSP bandwidth is
decreased to the crystal filter bandwidth, then that roofer is selected.
(Or, when the DSP increases beyond the current roofer's bandwidth, then the
next wider roofer is selected.)
It is important to note that the "roofer bandwidth" is specified by the user
in the K3 CONFIG menu, and you are not constrained to use either the
"marketing" bandwidth or the actual bandwidth of the filter. You can put in
any bandwidth you want because all you are doing is telling the K3 what DSP
bandwidth to engage that particular crystal filter.
Most users specify the marketing bandwidth of the filter, e.g., 250 Hz for
the 250 Hz 8-pole filter. So, as you decrease the DSP bandwidth and reach
250 Hz, that crystal filter will engage. (Or, if you select FLx, then
crystal filter 'x' is selected and the DSP bandwidth is set to 250 Hz.) But
you can specify 350 Hz, which is actually rational since the real bandwidth
of this filter is 370 Hz. Some people even specify a wider DSP bandwidth
engagement point such as 400 or 450 Hz, because they want their crystal
filter bandwidth INSIDE the DSP bandwidth.
So, think about the relationship of the two filters (crystal and DSP), the
resultant cascade bandwidth of the two, the shape factor of the two filters,
and the passband shape. Decide the DSP bandwidth at which you want your
particular crystal filters to engage. There are arguments for keeping the
roofer wider than the DSP at all times and vice versa. Remember that when
the DSP bandwidth is near the roofer's actual bandwidth, the cascade
bandwidth will be significantly less. When one is much narrower than the
other then the narrow bandwidth dominates the IF bandwidth, but other RX
characteristics like IMD performance will be determined by the roofer
bandwidth.
Setting the DSP engagement bandwidths for your crystal filters affects both
the resultant IF passband width, shape and "sound" of the audio, as well as
the RX performance characteristics such as IMD. If your head hurts thinking
about all this, just specify the bandwidth number in the part number of the
filter! That is a good default and the radio will work great.
Ed - W0YK
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