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

[wayne burdick]

On May 1, 2007, at 8:29 PM, Richard Lim wrote:

>>
>> 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.
>>
>>
>> 73,
>> Wayne
>> N6KR
>
> Wayne for reference, what is the width of the roofing filter in a K2?

Typically 200 - 2000 Hz (variable). You can get as low as 100 Hz, but 
with a lot of passband loss.


> Are we adjusting the roofing filters when we set FL1, FL2 etc in the 
> K2?

Yes.

"Roofing Filter" simply refers to the first very narrow filter in the 
receiver -- i.e. at the first I.F. In some rigs the first I.F. may be 
30-70 MHz, and that's why their roofing filters are limited to very 
wide bandwidths (3 kHz minimum, typically, and often as wide as 20 
kHz). Rigs with such wide roofing filters sometimes have narrower 
filters at a second or third I.F. (or both). However, some portion of 
the I.F. circuitry will be exposed to the area in the roofing filter 
passband, which is why

In the K3 the roofing filters *are* the narrow filters, since we 
down-convert to a low I.F. These narrow roofing filters have several 
advantages.

73,
Wayne
N6KR


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