[Elecraft] odds and ends...

[Jeff Herr]

Is signalink mono?












-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Bill Frantz
Sent: Monday, August 20, 2012 5:58 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] odds and ends...

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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