|From:||Marcus D. Leech|
|Subject:||Re: [Discuss-gnuradio] USRP Daughterboard bandwidth|
|Date:||Fri, 25 Jun 2010 19:00:00 -0400|
|User-agent:||Mozilla/5.0 (X11; U; Linux i686; en-US; rv:184.108.40.206) Gecko/20100430 Fedora/3.0.4-2.fc12 Thunderbird/3.0.4|
On 06/25/2010 01:31 AM, Matt Robert wrote:
PLL synthesizers often have a certain minimum resolution, or "step size". It varies by specific
daughter-card. That's a very, very, very conventional "problem" to run into. In many communications
systems, there's a standard "raster" that systems are set up on. In television, for example, channels
are 6MHz wide, so it's no unusual to find 6MHz or 3MHz as a minimum "resolution" for the
synthesizer. In amateur radio systems in VHF and above, channels are often 25KHz wide, so you'll
find synthesizers with 25KHz or 12.5KHz minimum step-size in the synthesizer.
The downconverter in the DBS_RX for example is designed for DBS (Direct Broadcast Satellite)
applications, where 1MHz and wider channel spacings are the norm, so the resolution of the PLL is
quite "coarse" compared to what you might find in a HF synthesizer for example.
Again, varies by daughter-card. The TV_RX, for example, has a 6MHz-wide IF filter, so you'll *never* get
more than 6MHz of useful bandwidth out of it. The DBS_RX has a programmable baseband filter that
goes anywhere from a coupla of MHz to 30MHz, depending on programming.
-- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org
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