John wrote:
> Alberto,
>
> With respect to the "TX side....!!" and your comment (below) " or
> SSB, in which case there will be the need to generate the two audio
> I/Q signals, starting from the microphone input."
>
> Do you require I/Q signals soundcard (software) generated or external
> hardware generated?
>
> John
> N3AAZ
>
John,
software, of course! Aren't we talking of "Software Defined Radios" ?
Seriously, there is an NCO (Numerically Controlled Oscillator), similar to that
already used in SDRadio for the final conversion to baseband, which generates
an audio frequency (e.g. 15 kHz) as an analytic signal, i.e. with the two
I and Q components. This signal is fed to a software mixer (nothing more than
a multiplication of complex numbers) together with the audio samples from
the digitization of the microphone signal. The two I/Q output signals are then
converted to analog form by the sound card DAC. From this point hardware
will carry on, and an upconversion to the operating frequency must be done
using either a QSD mixer, or a more conventional type (in this case it must
be a double mixer, for the image cancelling function, which the QSD
gives natively).
73 Alberto I2PHD
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