[Elecraft] Width of AM filter

[wayne burdick]

> Isn't there some way to just bypass the filter and rely on DSP?

Hi Steve,

We convert directly from our 1st I.F. of 8215 down to a 15 kHz 2nd I.F. 
(DSP). Without a narrow filter at the first I.F., you'd have an image 
response at 8215 + 15*2 = 8245 kHz that would pass through unimpeded. 
So you really do need a wide filter if you wish to copy AM at high 
fidelity, or to use FM at all.

Other transceivers incorporate wide filtering by default because they 
up-convert to a very high first I.F. where it's easy to make such 
filters. But this results in major compromises in receive performance.

We have the opposite strategy -- down converting to a low first I.F., 
which provides far better receive performance (by 10s of dB in some 
parameters). But this does require that each K3 user to determine 
whether they want to use wider-bandwidth modes, and the filters aren't 
cheap, because they're very high quality, requiring custom, matched 
sets of crystals.

I feel that we made the right tradeoff.

> I still would appreciate more bandwidth for CW. 2.7khz is far too 
> narrow for comfortable monitoring while working around the shack. I 
> know it takes some programing but from a layman's point of view, it 
> seems like a simple request and it would certainly improve the 
> product.

I agree, and this is on the MCU firmware list.

73,
Wayne
N6KR