Re: whither regenerative amplifiers?
From: Ken Smith (kensmith_at_green.rahul.net)
Date: 10/30/04
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Date: Sat, 30 Oct 2004 16:42:33 +0000 (UTC)
In article <puh6o0lpvkiotq4pbsgtin4ptv4g17h732@4ax.com>,
Paul Keinanen <keinanen@sci.fi> wrote:
[...]
>If we are talking about amateur band systems only, using suitable
>high-Q front end band pass filtering (helical or cavity resonators),
>you can limit the bandwidth to a few hundred kHz (e.g. the SSB or
>satellite band). Then you only need a sampling frequency of the order
>of 1 MHz and undersample (decimate) it and process it at that sampling
>frequency.
This method tends to increase noise unless something clever is done in the
area of the sample and hold. The device that does the sampling, must be
fast so there are a lot of sqrt(Hz) included. The sampling will alias the
high frequency noise from the device down.
You are better off to mix down to a lower frequency using something that
acts multiplying sinewaves so that there are no high frequency components
to cause the mixing of high frequency components. You can make sample and
hold circuits that act this way but you need more than one to make it work
right.
-- -- kensmith@rahul.net forging knowledge
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