Talbot Andrew wrote:
[snip]
IF filtering will be a 300Hz bandwidth mechanical filter at 455kHz.
Very extensive front end filtering is needed to remove the image
response which sits in the MF broadcast band at 910 - 1070kHz. 130dB
in total apportioned into two filter blocks either side of the front end
gain stage, Fc at 160kHz so that the 198kHz Droitwich signal is
attenuated by 20dB before it reaches the mixer. Needless to say, all LO
frequencies will be derived from one master 5MHz source.
[snip]
Andy, to solve one for all the image response problems, have you considered
going to the zero IF approach ? This method, using a single DDS for the
conversion,
and a couple of mixers to generate the I and Q components, will allow you to
enter
into a stereo 24-bit ADC and then to do all of the processing, whatever it may
be,
digitally in a DSP chip, keeping the analog portion to a bare minimum. You will
also
save the expense of the mechanical filters.
73 Alberto I2PHD
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