[RTTY] poor signals and soundcards performance/calibration

[f6irf at free.fr]

For having done some tests with an HF channel simulator, and parallel tests 
from real live signals I personaly don't have any doubt about the fact that DSP-
based decoders really outperform decoders with conventional analog filters 
(like the PK232, PTC2, etc)...
This was pointed out a few years ago by K6STI in articles about RITTY(for 
example the importance of the ATC, an the big difference it can make)

But I also confirm what Phil has mentionned here 
>I also suspect that the processing power of your PC, and maybe even the
>soundcard, might be a contributing factor in some cases.

For the processing power, I don't know, but for the soundcard I am sure!
-A good soundcard with low noise line input (like you can find on "home studio" 
quality soundcards) can make a difference with Cheap soundcards having just 
a microphone input. One obvious reason, is the substantial amount of noise 
added to the signal, when using the microphone input... 
-Many amateurs never thought about the calibration of their soundcard...By 
experience I know that a baddly calibrated sound-card card can really make the 
best decoder deaf like a stone (*).
Of course many other factors, starting from the receiver itself may also play a 
role, especialy when approaching the theoretical limit, but in general if your 
PK232 outperforms MMTTY, I think that you should first look at the a/m points.

CU in the SP-test - 73's Patrick


(*)For more details, refer to the MMTTY manual chapter "getting things to 
work"