Hi Phil,
The four switch QSD circuit you simulated integrates signal on four capacitors with two of the capacitor voltages summed to form the I or Q signal output. Thus it make good sense that when you simulate a two switch QSD each of the outputs will be cut in half, thus a 6dB gain reduction.
The SoftRock QSD circuit uses only two signal integrating capacitors, one each for the I and Q signals. In the v4.0 SoftRock, each capacitor voltage is refreshed two time per cycle and so the gain will be greater than your two switch simulation. Your two switch simulation is correct for the QSD gain of the v5.0 SoftRock.
I conclude my observation of a 3dB gain decrease when going from a v4.0 SoftRock to a v5.0 SoftRock is probably valid.
Interesting stuff. Thanks for your simulation and SDR software efforts.
73,
Tony KB9YIG
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----- Original Message -----
From: "Phil Covington" <p.covington@...>
To: <softrock40@...>
Sent: Wednesday, October 26, 2005 1:04 PM
Subject: [softrock40] QSD Models
Hi all,
I've placed some results of simulation of a two switch and four switch
QSD circuit on my blog at:
Check it out if you are interested in the QSD circuits.
73 de Phil N8VB
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