On 3/3/2014 7:18 AM, Charles Guenther wrote:
FD operators are not always good at zero beating, and we've found the wider
filters indispensable for hearing the off-frequency callers.
I've never used my K3 for Field Day; but I would sure use the 700 Hz filter.
I simply do not understand the desire for a 700 Hz ROOFING filter with a
K3. Remember that the switched crystal filters that we all used in older
rigs are replaced by DSP filtering in the K3 and KX3. All it takes to
get 700 Hz IF bandwidth is to turn the bandwidth knob!
The plug-in filters for the K3 are ROOFING filters -- that is, they go
in the first IF to protect the DSP from overload by VERY strong signals.
Roofing filters have the additional benefit of providing cascaded
filtering when the DSP IF is set to the same bandwidth as the roofing
filter. "Cascading" means that the filter slopes of both filters
additive. If, for example, the DSP IF is down by 10 dB at 400 Hz from
center and the roofing filter is down by 8 dB at 400 Hz, the combined
rejection is 18 dB.
I do a LOT of contesting, most of it on CW, and I almost never use IF
bandwidth greater than 400 Hz, and most often 250 Hz. Based on advice
from designers of RTTY decoding software, I've gone to 400 Hz bandwidth
for RTTY, and no longer use the dual-peak filter. With my first K3 I
bought 400 Hz and 1.8 kHz filters. A year or so later I added 250 Hz. I
have the K3 set to switch to the 250 Hz filter at 320 Hz DSP bandwidth,
and most of the time it is engaged. I've also found that I almost never
set the IF narrower than 2.2 kHz for SSB, and that the 1.8 kHz roofing
filter is too narrow.
Bottom line -- a 700 Hz roofing filter for a K3 is a solution in search
of a problem. If you think you need one, you're either doing something
quite unusual, or you probably don't understand how the K3 works.
73, Jim K9YC
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