Hi Don,
At 08:47 PM 5/4/07, Don Wilhelm wrote:
I did ask Wayne about the AGC (with respect to the roofing filter
selection) and he indicated that the AGC was developed in hardware
before the A/D conversion and there is additional AGC action created
in the DSP. As I understand it, it is similar to that which you
describe in the Orion.
If it is like Orion's I'll be happy!
Yes, from a receiver performance standpoint, only the A/D overload
problem counts (and it is critical), but from an operating (AGC
pumping) standpoint, there can be undesired performance in the
presence of strong signals that pass through the roofing filter even
though they are filtered out by the DSP because they will reduce the
overall gain of the receiver. Quite apart from the receiver specs,
it does show up during operation and the AGC pumping can be a real
problem for weak signal reception regardless of the total dynamic
range of the receiver.
I'm not sure I agree. If analog AGC is
not activated, there is no analog gain change or
pumping. According to the note I posted from
Doug Smith, the DSP can internally handle AGC
within the ballpark of 100 dB (noise floor to S9+40).
It first filters signals digitally and then applies AGC
only to signals appearing within the selected DSP
bandwidth, so there is no pumping by signals
outside the DSP bandwidth...unless I misunderstand
...which is completely possible of course!
All I can say is I have never experienced
the problem in Orion. I've got to get ready for a
symphony concert now so hopefully all will be
answered in the fullness of time!
73, Bill
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