[Elecraft] [K3] Roofing filters are misunderstood

[Joe Subich, W4TV]

> I can remember very loud stations 10 or 15 KHz away completely
> desensing my receiver to the point that the station I was trying to
> copy simply disappeared. When I switched to the K3 the difference
> was astounding.

That is because the 756Pro is a completely brain dead design ... there
is only a single 30 KHz or so roofing filter at VHF and AGC which is
based on total signal in that 30 KHz or so "window" starts at a very
low level.  The only job of the K3's *hardware AGC* is to protect the
analog to digital converter from being driven into saturation so it
does not begin to activate until approximately S9+40.

The K3's normal AGC is entirely DSP based and is effectively
controlled by only the signal which passes through the DSP (it is
a shame the AGC control point isn't also after the notch <G>).

73,

    ... Joe, W4TV


On 5/11/2014 10:02 PM, David Gilbert wrote:
>
> I completely agree with all of that except for the very last sentence.
> Clearly you've never used a 756Pro (first version) in a major CW
> contest.  I can remember very loud stations 10 or 15 KHz away completely
> desensing my receiver to the point that the station I was trying to copy
> simply disappeared.  When I switched to the K3 the difference was
> astounding.
>
> 73,
> Dave   AB7E
>
>