rejection ... so does the RX320 which cannot do sideband in hardware
due to a hardware 1st LO with 2.5Khz steps using a 10Khz filter (main
purpose is image rejection not sideband rejection) bandwidth and fixed
2nd and 3rd LOs it is impossible to to place the sidebands on the
filter slope to filter out the opposite sideband, not to mention there
is no way to select the sideband you want because the 1st, 2nd and 3rd
LOs are the same whether you are in AM CW USB or LSB modes ... If you
measure the opposite sideband rejection using the 320's 12Khz output
and Alberto's program you'll find it's far less than 30 db but with
the I-Q generation in the built-in software the 320's opposite
sideband rejection exceeds 60 db ... no other way to explain that
other than the 320 does it's I-Q generation and sideband rejection in
software (Plus a couple of Ten-Tec engineers told me about the I-Q
generation in software which they've been doing since the early 90's
in their commercial DSP receivers) .... it's also why neither the
STAR or the RX320 use a zero IF but actually use a 12Khz or 15Khz IF,
I-Q generation in software won't work with a zero IF from what I've
been told ... If I remember right Bob Larkin's DSP-10 2 Meter
transceiver generated it's I-Q in software also
You can see the STAR's software block diagram in the 2nd part of the
series and it clearly shows I-Q generation in software .... the key is
they mix to baseband in software not hardware and the generation of a
15Khz I-Q lo and the mixers in software isn't that tough ... from
there the software is essentially like the hardware I-Q versions
You can join the STAR Yahoo group and all the details are in the files
section, including the DSP source code
JR
--- In [email protected], "jabauzit" <[EMAIL PROTECTED]> wrote:
>
> --- In [email protected], "i2phd" <i2phd@> wrote:
> >
> > There is no way out, unless the
> > external hardware operates in quadrature, no software magics can
> > recreate those I/Q components that haven't been generated by the
> > hardware, and the two sidebands are by now irremediably mixed
together.
> >
> If I understand you correctly, a TRX like the Pic-A-Star which
> extracts the I/Q components in the DSP works because the image has
> been removed by the preceding stages and the I/Q channels are used
> only for demodulation, not image rejection.
>
> Jean-Claude PJ2BVU
>
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