[hpsdr] Call for Comments and Discussion - CYCLOPS

[David McQuate]

While a higher second IF choice (like 906MHz) helps rejection of images
due to non-brick-wall filters, it requires removal or bypassing of the 55MHz
low-pass at Mercury's input.  For "normal" operation as a receiver, an
external low-pass would be required.  -- On the other hand, placing the 
filter
externally opens up the option to extend Mercury's frequency range up to
and even beyond the sampling frequency.  (There's also the preamp to be
considered...)

If a lower 2nd IF frequency were chosen (say "zero" to 55MHz) no 
modification
would be required to Mercury, and a much larger chunk of spectrum could be
acquired at a given first LO frequency.  This opens the possibility to 
use Cyclops
as a down-converter for higher frequency reception (to 1GHz).  It seems 
to me that the
second IF would be defined by Mercury's low-pass filter.  A band-pass filter
would not be necessary.  The lower end of the 0-55MHz range might be of
less use, because of finite filter slopes, due to inadequate rejection 
of the image
frequency in the second mixer, so the useful bandwidth might be 10-50
or 20-50MHz.

73,
Dave wa8ywq


Graham / KE9H wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> All:
>
> An information package has been posted to the Wiki on the
> CYCLOPS page, under the "July 11 Update" heading, with
> block diagram, schematics and a proposed PCB layout for
> a prototype CYCLOPS spectrum analyzer card.
>
> The Tracking generator will likely be a separate card developed
> after the main SA receiver card is running.
>
> Please review the package and direct questions, comments,
> constructive criticism, etc to Phil, VK6APH or myself. Phil is the
> project leader and designer.  I have been assisting Phil with
> the PCB layout, bill of materials and sourcing.
>
> --- Graham / KE9H
>
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