[Elecraft] K3 Receiver mush

[Don Wilhelm]

Dave,

Yes, a 400Hz filter will work well for RTTY (and CW too).

73,
Don W3FPR

On 2/21/2017 6:27 PM, Dave Fugleberg wrote:
> Don, that's a great explanation. I came to the same conclusion in a 
> recent RTTY contest. I built my K3 with the single stock filter based 
> on advice from a number of folks to 'just operate for awhile til you 
> get the feel for what other filters you need'. I think that's sound 
> advice.
> Anyhow, I've been generally ok with the standard filter and relying on 
> DSP filtering to narrow it as needed. However, in the RTTY contest, I 
> often had issues working weaker stations when strong ones were very 
> close by. It was easy to see what was going on by watching the P3- I'd 
> start copying a signal inside the DSP bandwidth, and a strong one 
> would pop up just above or below that station. Even though I couldn't 
> hear the strong station, the weak one would go nearly silent as the 
> AGC kicked in due to the strong signal in the IF passband.
> So, I think I've learned that I need a narrower filter for such 
> situations. I'm thinking a 400hz filter is what I want. Any reason for 
> a different selection in that scenario?
> 73 de W0ZF
> On Tue, Feb 21, 2017 at 8:52 AM Don Wilhelm <donwilh at embarqmail.com 
> <mailto:donwilh at embarqmail.com>> wrote:
>
>     Mike,
>
>     Think about it - if there are multiple signals in the passband,
>     the AGC
>     will respond to the strongest, there is just no way around that fact.
>     If the signals can be separated by the DSP, and one is really strong,
>     that strong station may be activating the Hardware AGC.  The only
>     solution for the latter is a more narrow roofing filter - put the
>     offending strong signal out of the passband of the roofing filter and
>     use shift to get your sidetone for the desired signal back in order.
>
>     That may be too much "fiddling" for a run station in a contest, but it
>     is a viable way to operate when trying to copy a weak station working
>     close to a strong station.
>