[Elecraft] odds and ends...

[Bill Frantz]

Using a SignaLink USB interface, I often see cocoaModem 
reporting input overload from strong signals on 20 meters with 
the noise barely visible on the waterfall. This occurs with both 
the K3 and the Small Wonder Labs PSK-20 driving the system. (The 
Icom 706 MK2G generates a lot more noise.) I reduce the gain on 
the SignaLink, or with the K3 on the RF gain, but that pushes 
weak signals too low to decode.

I am willing to accept that the SignaLink isn't a good sound 
card, but need evidence/alternatives.

Cheers - Bill, AE6JV

On 8/20/12 at 22:08, lists at subich.com (Joe Subich, W4TV) wrote:

>With real receivers you probably will never notice the difference in
>dynamic range between a 16 and 24 bit sound card.  The receiver AGC
>- even only modest AGC - will keep the dynamic range presented to the
>sound card well within anything the 16 bit sound card can handle.
>That is *unless* the 16 bit card is poorly designed with internal
>noise that wastes a significant part of the 16 bit range.
>
>Even without AGC, the range between "background noise" (the noise
>floor of the demodulation process including sky noise, thermal
>noise in the IF, etc.) and the clipping point of the audio output
>can be considerably less than 90 dB in "real" receivers.  Audio
>output levels tend to range from around 10 mV with "no signal" to
>just under 5V P-P (2V RMS) at best ... that's less than 50 dB.
>Even if one assumes the software can decode a 1 mV signal in the
>10 mV nose floor, the resulting dynamic range is still much less
>than 90 dB provided by a properly designed 16 bit sound card and
>unless the 24 bit soundcard uses other than the typical 5V power
>supply, its real performance will be limited by the same 5V P-P
>audio levels!
>
>Taken a step further - if the receiver produces a 1 mV noise floor
>with 24V P-P output (+/- 12V supplies), that's *still* less than
>90 dB of range.
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