RTL-SDR: E4000 IF bandwidth (& Slashdot!)

Balint Seeber balint256 at gmail.com
Sun Apr 1 02:53:27 UTC 2012


Hi Michal,
Thank you for asking the question - I was thinking about this too last night
(actually this morning) while I was trying to catch up on some sleep, but my
brain wouldn't stop ticking over :)

Can't be sure of the effect as datasheets aren't public, but I will
experiment with narrowing the bandwidth. The 'IFfilter' function in the
E4000 tuner code is made up of a massive if/else block that sets various
register values by checking the input IF-BW values from <= 2150 to > 5500,
so it appears to support a wide range (despite the convenience
'E4000_BANDWIDTH_HZ' enum in the header).

Will post findings a little later, unless someone beats me to it :)

Kind regards,
Balint

PS: "Software-Defined Radio For $11" on Slashdot!
http://hardware.slashdot.org/story/12/03/31/1914217/software-defined-radio-f
or-11

PPS: I've been working to improve the GNU Radio Source block and Windows
plugin with generous feedback from the community. Grab them here if you
wish:
http://wiki.spench.net/wiki/gr-baz#rtl_source_c
http://wiki.spench.net/wiki/USRP_Interfaces

> -----Original Message-----
> From: Michał Rogala [mailto:michal.rogala at gmail.com]
> Sent: Sunday, 1 April 2012 4:36 AM
> To: balint256 at gmail.com; osmocom-sdr at lists.osmocom.org
> Subject: RTL-SDR: E4000 IF bandwidth
> 
> Hi!
> 
> I've just noticed one issue about E4000 driver that bothers me - IF
> bandwidth at the chip is set to 8 MHz, where maximum bandwidth of RTL2832U
> sampling is 3.2 MHz.
> 
> Wouldn't reducing IF bandwidth at tuner chip improve overall sensitivity
> (and maybe noise level)?
> 
> best regards
> 
> Michal Rogala





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