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What about strong signals within the same band? The impression I get
(from criticisms I've read) is that the wideband ADC approach is
particularly susceptible to cross-modulation from such signals, and
that it's too late to apply filters in software. Is this fair? If so
can ALEX step in and help with this problem?<br>
<br>
Murray VK6HL<br>
<br>
<a class="moz-txt-link-abbreviated" href="mailto:pvharman@arach.net.au">pvharman@arach.net.au</a> wrote:
<blockquote cite="mid1173233218.45ee1e426623d@webmail.arach.net.au"
type="cite">
<pre wrap="">***** High Performance Software Defined Radio Discussion List *****
Hi Graham,
Thanks for taking the Project Leader role on for Alex. Re your request
below, based on my tests with the prototype Mercury setup the native
performance should be very acceptable without any additional input filters. The
Mercury board contains a switchable 1.5MHz HPF and 55MHz LPF to remove high
level MW broadcast signals and prevent VHF signals from aliasing into the
passband.
I live in an area close to multiple MW broadcast stations and with the HPF in
circuit have no problems on any HF band. If I want to listen on MW then I will
bybass the HPF and if necessary turn off the preamps and use the 0-30dB
attenuator.
I used the Mercury prototype on 40m during the recent ARRL CW contest. As I
test I mixed an S9+60 db signal in with the antenna and at 1kHz spacing could
still copy a signal at the noise floor. The limit of the test was the sideband
noise of my HB8640B not the receiver strong signal performance.
Since we have little practical experience in using direct digital conversions
receivers (and having a frontend fully open from 1.5 to 55MHz does not feel
right to an analogue receiver designer!) Alex is there in case folks live in a
high signal environment, require additional front end selectivity for contest
or DXperdtion operations etc. I suspect that in many cases with the natural
selectivity offered by antennas, ATUs, HF beams etc then Alex may not be
required.
73's Phil...VK6APH
</pre>
<blockquote type="cite">
<pre wrap="">I assume the majority of the users want good ham band performance
and casual SWL, WWV, and experimental capability. The
native performance of the underlying SDR should be good
enough for the "casual" and incidental uses with the preselectors
bypassed. [ Phil H, please comment. ] Any serious or focused
other uses can put a dedicated filter section in the user
defined spaces, or rework the whole filter pack. The PCB
layout will accommodate third order (three inductor)
bandpass or low-pass filters in each section.
</pre>
</blockquote>
<pre wrap=""><!---->
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</pre>
</blockquote>
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