[hpsdr] Fwd: ISD for SDR

[Ahti Aintila]

Hi Phil,

As your simulation shows:
<http://pcovington.blogspot.com/2005/10/qsd-simulation.html> the
voltage gain of the ISD depends on the duty cycle. My understanding is
that your simulation had same component values for all duty cycles.
However, for the maximum signal power transfer the input impedance of
the integrating circuit should be optimized for the actual duty cycle
and good match with the source impedance.

73, Ahti OH2RZ


---------- Forwarded message ----------
From: Ahti Aintila <oh2rz.sdr at gmail.com>
Date: 30-Aug-2006 10:34
Subject: [hpsdr] ISD for SDR
To: High Performance Software Defined Radio Discussion List <hpsdr at hpsdr.org>


Hi all,

After a lot of private mailing and experiments with the Active
Integrating Quadrature Sampling Detector concept, I think it is the
time to put my results under the public criticism. Unfortunately, my
previous sending bounced back due to too big attachments, so you
should see the links:
<http://kotisivu.dnainternet.net/ahti/sdr-1000/AIQSDb.pdf>
<http://kotisivu.dnainternet.net/ahti/sdr-1000/isdbrd.jpg>.

Against the common practice and opinions I have used 50% wide I and Q
sampling pulses instead the 25% pulses, because those wider pulses are
readily available without any extra decoding in proper form to the
selected two fast SPDT sampling switches.

Please, understand that my circuit is not necessarily best optimized
for the purpose, but I feel that it is a good starting point for other
experimenters. Already now I can suggest few dB more internal gain for
the ISD so that no post amplifier would be needed before the sound
card (provided that the sound card has differential inputs).

73, Ahti OH2RZ

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