[Icom] PSK31 and sound card question.

[Chris Smolinski]

BielefeldJ@andovercontrols.com wrote:
> 
> I use a compaq PC with a built in sound chip ESS Technologies ES1869F.
> It is supposed to run of a 14.31818Mhz clock. When I measured the clock
> input to the sound chip I measured 14.31954Mhz using a frequency counter.
> 
> The problem I have is, I have garbled text displayed even on strong signals.
> 
> How important is the clock frequency accuracy for receiving PSK31?
> The clock on this board is difficult to tell where it is generated as I can not
> find any 14.318  crystal oscillator. I'm tempted to unsolder the X0/X1 sound chip
> clock input/output pins and build an off board crystal oscillator with
> higher precision.

14.3... MHz is a standard clock frequency found on the PC AT bus. It is
probably derived from some other clock.

Assuming your freq counter is correct, you have a difference of around
95 ppm. For the [nominal] 1 kHz PSK31 audio carrier frequency, this
would give you an error of 0.095 Hz after sampling. Is the SSB tuning
precision on your rig superior to that? If not, this is a non-issue. 

73
Chris
N3JLY