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Re: [linrad] For general interest
Tks vy much for the info.
The ( probably expensive) mixer, however, may have impressive IP3 figures
but one has to account the rather bad 16-19 dB noise figure is order to get
an idea of its dynamic range.
----- Original Message -----
From: W6WO <ron-skelton@xxxxxxxxxxx>
Sent: Monday, August 18, 2003 9:27 PM
Subject: [linrad] For general interest
> Here are a few sites that might be useful
> For comparing sound cards
> The Skyworks SKY73001-11 (http://www.skyworksinc.com/) is an
> interesting device designed specifically for direct conversion I-Q
> receivers. Brief specs are
> RF 2 -3500 MHz
> IF 0 -100 MHz
> IIP3 +26 dBm
> IIP2 +67 dBm
> I have been looking at the noise specifications of various DC
> regulators which could affect base-band noise levels, there is a wide
> range. In summary
> At the high end the LM 317 and 337 series have RMS noise levels of
> 0.003% of Vout. The spec states this is over 10 Hz to 10 KHz
> The best I could find from Motorola was the MC1723C that seems to
> have very low noise (2.5 uV) this is stated over the range 100 Hz to
> 10 kHz
> The MC78L/79L 100 m/A series have noise levels 5V/40 uVrms, 12V/75
> uVrms, 15V/90 uVrms stated to be in the 10-100 kHz range.
> It is reasonable to expect these levels could be reduced by Tantalum
> capacitors at the device output but it seems smart to select low
> noise devices to begin with.
> For further immunity the spec for the AD797 amplifier recommends 0.1
> uF and 4.7uF capacitors at the + and - supply pins with <5 mm leads
> to ground.
> Now a question.
> In most I-Q demod designs I note the phase shift is applied to the
> LO. In the simple 40 kHz 2x SBL-1 design that Leif published in QEX
> the shift is applied to the RF. What is the reason for this approach ?