> a) Is 26dB a reasonable S/N ratio for a built-in mother board sound
> card?
Your signal to noise ratio is not 26 dB ... it is 56 dB ("S9" audio
level minus no input noise level) but you're not using the entire
dynamic range (noise floor to clipping) of the sound card. 56 dB
is about as good as you can expect to see in any system with AGC.
In general the K3 shows about 20 to 25 dB change in audio output from
MDS (-145 dBm) to S9 +20 dB (-53 dBm). You might see some improvement
by adjusting the K3 audio output to be lower with no signal (-90 dB)
and adjusting the AGC THR/AGC SLP settings so that S9 +30 dB (onset of
hardware AGC) reaches -40 dB or a total dynamic range of 50 dB. The
real question is whether the K3 Line Out will remain clean over the
entire 50 dB range and whether the operator can tolerate that range
of audio or the resulting maximum level.
> b) How much could I likely improve the S/N ratio with a better
> quality sound card?
None ... you're not close to using the real dynamic range of even
a poor sound card since most transceivers have an audio output range
of only 30 to 40 dB. Note - the microHAM interfaces have a dynamic
range (internal noise floor to clipping) greater than 96 dB.
73,
... Joe, W4TV
On 6/2/2011 8:42 PM, RLVZ@aol.com wrote:
> Hi Guys,
>
> Thank You for your recent comments regarding 75 Baud RTTY. I think I'm
> ready to "go at it" this weekend.
>
> I am trying to check out the performance of my computers sound card
> running RTTY with MMTTY and using a K3 for the receiver and Spectran audio
> analyzer software. Here are the numbers I'm getting:
>
> 1) Cable to sound card input disconnected, noise floor averages -100dB.
>
> 2) Cable connected from K3 rcvr to sound card input but no signal, noise
> floor averages -70dB.
>
> 3) Same as #2 above but with an S-9 signal, signal averages -44dB or 26dB
> above the no signal noise floor.
>
> QUESTIONS:
>
> a) Is 26dB a reasonable S/N ratio for a built-in mother board sound card?
>
> b) How much could I likely improve the S/N ratio with a better quality
> sound card?
>
> Thanks& 73,
>
> Dick- K9OM
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>
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