Craig,
The AGC pumping will not happen if the undesired signal is within the
spectrum of filter ultimate rejection. Any filter worthy to be called a
filter (even a poor one) will have an ultimate rejection of 60 dB or
greater - the K3 filters plots show ultimate attenuation in the 78 dB or
greater range.
As Vic pointed out in a related post, the hardware AGC only kicks in if
the DSP will be overloaded, so as long as the undesired signal is
outside the filter passband (by definition, that is the area of ultimate
rejection for the filter) the unwanted signal will be severely
attenuated and should not activate the hardware AGC. Yes, the K3 is
different than the Orion.
If OTOH, you are concerned about a signal somewhere on the filter slope
(say 20 dB down), then you may encounter an AGC pumping problem, but
that has to do with the steepness of the filter slope and is much
different than the ultimate rejection that you indicated you were
concerned about.
73,
Don W3FPR
[EMAIL PROTECTED] wrote:
In a message dated 9/18/2007 4:36:17 P.M. Eastern Daylight Time,
[EMAIL PROTECTED] writes:
If the roofing filter is able to knock down the
unwanted signal to a level the DSP can handle, then the DSP will not
overload and the DSP itself will provide great ultimate rejection.
Well, sorta kinda. If the unwanted signal gets in and pumps the AGC, then
the DSP might knock down the signal but won't be able to do anything about the
AGC pumping. Then, you won't hear the signal if it is weak. That is the
whole issue of the DSP being in or out of the AGC loop and it generated a
mountain of controversy with the Orion when TT moved the DSP to within the loop.
I believe I read the K3 did not follow that mistake but a little
clarification from the gurus who know a whole lot more about this issue would be helpful.
Craig "Buck"
k4ia
Fredericksburg, Virginia USA
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