[Elecraft] Regarding PSK31 and K2 Filters and KDSP2

[Julian (G4ILO)]

I have been using digital modes since 1999 and I have to say my experience 
is not the same as yours. It's not a question of how much power they are 
running, but how strong they are. Even a 5W signal can be S9.

A strong PSK signal can easily make weak ones disappear from the trace and 
switching to the narrow filter *does* improve the copy as I've frequently 
proved.  A strong signal in the filter passband activating the AGC is going 
to depress the strength of the weak signal you're trying to copy, no 
argument. I suppose you could disable the AGC, but that's an extra thing to 
do when changing modes, and you'd probably run into problems with 
overloading the sound card due to the large changes in audio level you'd 
then experience.

The suggestion of using the KDSP2 to remove a strong signal won't make a 
difference. A strong audio signal won't "annoy" the sound card, as you put 
it. A strong RF signal will reduce the gain of the receiver, which will 
reduce the S/N ratio of the wanted weaker signal, resulting in poorer copy. 
What might help is IF DSP reducing the strong signal so it doesn't have any 
effect on the AGC.

Actually, I don't see how the use of KDSP2 in data modes can improve copy 
at all. The data mode program itself is using DSP. It will simply ignore 
noise, signals on other frequencies and so on that may bother our ears. The 
only thing the computer can't do is decode a signal that isn't there, and 
that will occur more often if a strong signal elsewhere is reducing the RX 
gain. The KDSP2 can't help there.

I think the best the KDSP2 can hope to do is not make copy any worse in 
data modes. I think Lyle's decision to have it disabled in RTTY mode is the 
technically correct one, although there's probably an argument for letting 
users have the choice and deciding for themselves.

The bottom line is, I don't think PSK is different from any other narrow 
band mode - it's best received using a narrow band filter so as to get the 
best S/N ratio, whether it's your ears or a computer that are doing the 
decoding.
--
Julian, G4ILO. (RSGB, ARRL, G-QRP, K2 #392)
G4ILO's Shack: http://www.qsl.net/g4ilo

Joe Squarzini <k4aa@verizon.net> wrote:

I have been operating all digital modes on the K2 for about one year. 
Despite all the reflector chat on various filter setting methodologies, I 
have found that leaving the K2 on OP1 all the time is optimum. Rarely have 
I found AGC pumping so serious that I could not copy a weak signal. If a 

[snip]

Most digital stations are using 
low power. I worked a ham last night during immense static crashes here on 
the East Coast: he was running 3 watts! 

[snip]