Message-ID: <3A59A12E.711D7982@usa.net>
Date: Mon, 08 Jan 2001 12:14:54 +0100
From: "Alberto di Bene" <dibene@usa.net>
Organization: Undisclosed
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To: rsgb_lf_group@blacksheep.org
Subject: LF: RE: LF Receiver
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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