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Sun Nov 25 16:08:01 EST 2012

Trying out rtl-sdr

* FM radio demod works.  (Q: how to sync the sampling rates of dongle
  & audio card?)

* I have a Rafael Micro R820T tuner[1]:

  These tuners cover 24 MHz to 1766 MHz (locking again with lots of
  gaps from 1850-1860 and 1900-2100). They also don't have the DC
  spike caused by the I/Q imbalance since they use a different,
  non-zero, IF. On the other hand, they might have image aliasing due
  to being superheterodine receivers.

* Did some scanning using FFT view and NBFM demod.  Found a beakon at
  453.433M and multiple NBFM dispatch.  453.19M Police radio?  Found a
  reference here[3].  Real frequency seems to be at 453.21250.  Error
  is is 50ppm.  One of these constant ones is probably a DMR, probably
  the trunking data line[6].  There's some on 866MHz too.

* Found headphones at 911.03MHz.  NBFM doesn't work.  WBFM?
  Actual chan 1,2,3: 912, 912.5, 913 MHz

* How to calibrate?  Maybe local broadcast FM radio is best.  Tuning
  on 90.5 / 99.9 MHz when talk radio is on seems best, this makes the
  sidebands quite visible on a sharp FFT.  I'm at 100ppm correction.
  
* A bunch of narrow-spaced carriers at 149.7Mhz

* Very strong blip at 433.750, 1/minute

* Strong signals at 866MHz, 930MHz




[1] http://superkuh.com/rtlsdr.html
[2] http://discovermagazine.com/2007/jun/tireless-wireless/allochrt_lg.jpg
[3] http://www.radioreference.com/apps/db/?ctid=1259
[4] http://apcointl.org/spectrum-management/resources/spectrum/low-power-450-470-mhz.html
[5] http://upload.wikimedia.org/wikipedia/commons/4/45/United_States_Frequency_Allocations_Chart_2003_-_The_Radio_Spectrum.jpg
[6] http://www.youtube.com/watch?v=J5lNw4F4SFQ

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