Beginner question about rtlsdr

historical

Hello

May I suggested a few things not related to the "Programming" issues but
related to the Radio Astronomy subject? Just like retail, about "Location,
Location, Location," Radio Astronomy's is about the "Antenna, Antenna,
Antenna." One thing the TV Dongle offers for Radio Astronomers is the ease
of placing the receiver (Dongle) on the Antenna. The USB must be extended
from the Computer to the Antenna, instead of bringing the Signal from the
Antenna to the Dongle. The advantage is lower noise and higher gain (without
noise). There are many references on the Internet for extending USB, some
for purchase, some DIY. 

Extending the USB is not limited to Radio Astronomy...

-----Original Message-----
From: osmocom-sdr-bounces at lists.osmocom.org
[mailto:osmocom-sdr-bounces at lists.osmocom.org] On Behalf Of Michel Pelletier
Sent: Sunday, October 21, 2012 12:25 PM
To: osmocom-sdr at lists.osmocom.org
Subject: Beginner question about rtlsdr

Hello everyone, I hope this is an appropriate forum for a beginner question
about using an E4000 dongle.

I'm an amateur astronomer, and lately I've been wanting to get into amateur
radio astronomy.  The rtlsdr seems like a really cheap way to get involved.
It can tune many interesting frequencies, in particular channel 37 around
608-614 Mhz.

I am a Python programmer by trade so I am using roger-'s amazing pyrtlsdr
library which is great, I can read samples from the device and they get
returned as numpy arrays.  The scipy.signal package allows me to correctly
decimate the signal and I am working on a simple graphing program to graph
signal levels in realtime, by hour, by day, and by week.  I hope to
basically reproduce the Jansky experiment that started the entire science of
radio astronomy:

http://en.wikipedia.org/wiki/Karl_Guthe_Jansky

I have a question though about how to use the dongle that I can't quite
figure out.  roger-'s demo_waterfall program, for example, sets the default
sample_rate to 1.4e6, but then on each scan only calls read_samples(2**16).
The demo displays the entire megahertz of bandwidth, so I'm a bit confused
as to how the 64K samples map onto the 1M samples of the device.  It doesn't
seem to make sense taht the device only returns the first 64K samples.  Can
anyone clue in a total beginner on the sample rate and reading samples from
the device correlate?

Thank you!

-Michel

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