[Elecraft] Re: roofing filters - when to use them

[wayne burdick]

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


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