Bill Tippett wrote:
Ken there are two issues here. You are
talking about how the ear/brain processes signals
in noise....
The second issue (the real one which
roofing filters address) is the generation of
spurious products within the receiver itself
which can interfere with the desired signal.
...
Ken,
There is a third, equally important issue, and this is often the
dominant one during contests or in pile-ups: Very strong interfering
signals within the passband of the roofing filter can de-sense the
reciever (or at minimum pump the AGC) by overloading stages after the
filter (I.F. amp, second mixer, A-to-D converter and its buffer, DSP,
PIN diode attenuators, etc.).
I can't count how many times K2 customers have told me that their
"other" rig (I won't list them) was useless in the presence of strong
signals, while the K2, with its narrow roofing filters, completely
eliminated this effect. The K3 also has this advantage.
A narrow roofing filter -- compatible with the communications bandwidth
required -- will protect "downstream" stages. The K3's
shift/width/hicut/locut controls automatically select and properly
position the optimal roofing filter. You'll see the FL1-FL5 icons
selected as you rotate these controls.
73,
Wayne
N6KR
---
http://www.elecraft.com
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