RE: Beginner question about rtlsdr

Hello Michel OK, I see you are way ahead of me. However, I have some experience using these TV Dongles, they have pitfalls. Number one is its frequency Accuracy, out-of-the-box; needs calibration. Another is that its frequency accuracy drifts over time and from the Ambient temperature necessitating periodic offset calibration. While it is possible to create a compensation cure for frequency drift vs. temperature, it may be far more prudent to place the Dongle in a temperature controlled enclosure (50C Heater) keeping it above the ambient to help prevent drift, in your case, the all too important Temperature related Phase Shift. I have thought of disconnecting the Dongle's Crystal and placing it in a Crystal Oven, but I have not tried that. The Entire Dongle is small enough to place it in a temperature controlled enclosure which also keeps it dry. -----Original Message----- From: osmocom-sdr-bounces(a)lists.osmocom.org [mailto:osmocom-sdr-bounces@lists.osmocom.org] On Behalf Of Michel Pelletier Sent: Sunday, October 21, 2012 8:22 PM To: Jay Salsburg Cc: osmocom-sdr(a)lists.osmocom.org Subject: Re: Beginner question about rtlsdr On Sun, Oct 21, 2012 at 5:50 PM, Jay Salsburg <jsalsburg(a)bellsouth.net> wrote: DIY. Thanks Jay, I'm personally fascinated by the scientific aspects of the subject so I do appreciate your comment. I'm not sure if you're referring to the link I posted in this thread to a picture of my telescope, but I did as you suggested an embedded the dongle directly in the cantenna. My extension is a simple usb cable as my computer is just across the wall, although for my next antenna on the other side of my property, I intend to use a small dlink access point device flashed with openwrt and using usb over IP and power over ethernet to extend the other data source to my computer. This will give me a single interferometric baseline to begin using packages like aipy. I have the parts, I'm still piecing together the receiver. I live in Western Oregon so weatherproofing is key. :) FWIW the EOR array uses simple, omnidirectional crossed dipoles and Python: http://eor.berkeley.edu/ That's a pretty gorgeous picture of Centaurus A for some simple dipoles! Here is an excellent presentation on the python technology behind it: http://setiathome.berkeley.edu/~aparsons/papers/2008-08-10_LFSW_AIPY_Present ation.pdf there are some pretty pictures at the end. All of the software parts of the interferometry are basically done, what is needed is to vet the possibility that something like an rtlsdr dongle and a simple antenna, arrayed across an area, can produce data of sufficient quality to feed into a package like aipy. As roger-'s ecellent pyrtlsdr can already capture dongle complex data directly into numpy arrays, it seems like all the pieces are laying around, simply needing to be put together, and I intend to try it. As an update, thanks to Scott's great help I am currently dumping data at 1420 Mhz center frequency into numpy arrays and averaging their squares. Here's the simple "core" of my loop: while True: yield numpy.average(numpy.absolute(radio.read_samples(2**20))) I'm accumulating one average per secondish and dumping them into a data file that I am plotting on a simple graph. Cassiopeia reaches maximum at my local position around midnight, and the graph is currently trending upward. I'm really hoping that by morning I'll have a nice curve that peaks at midnight and hopefully not a bunch of random squiggles. :) -Michel ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2013.0.2741 / Virus Database: 2614/5846 - Release Date: 10/21/12