[Elecraft] Curious -- why is KXFL3 roofing filter an option on KX3 ?

[Wayne Burdick]

Hi George,

Tight matching is required in the roofing filters because of their impact on the I and Q receive channels. This is not unique to Elecraft's application. By matching the gain and phase within the channels, we suppress image responses in hardware, simplifying the task of the DSP after the A-to-D converter.

Fortunately the capacitors come on SMD reels and have fairly tight tolerance within batches. So we sort them the same way we do crystals.

But yes, it would be difficult for a customer to repair their own KXFL3 board, should it involve the tight-tolerance parts. On the other hand, the board is extremely unlikely to fail, and it's a small removable module that can easily be replaced if necessary. I don't know of any cases of this yet.

73,
Wayne
N6KR

On Apr 11, 2014, at 9:26 AM, george fritkin <georgefritkin at yahoo.com> wrote:

> Matching 0.1% capacitors?  What kind of a design is this that requires such tolerances ?  This make maintenance almost impossible.
>  
> George, W6GF