Simple APT decoder prototype

I have wanted to implement a simple APT decoder for the NOAA weather satellites in GNU Radio for quite some time now, in particular since the USRP equipped with a TVRX or WBX daughterboard and a GNU Radio FM receiver can be an extremely good receiver for this purpose. Today I have spent some time looking at the details of decoding APT and actually ended up with a working prototype implemented using the GNU Radio Companion.

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GNU Radio 3.3.0 on Mac OS X – USRP

I have now tried the USRP on Mac OS X using the MacPorts installation and I am happy to report that it works very well. Indeed, the USRP is really plug and play on OS X and there is no need to configure udev or anything like it is the case on e.g. Ubuntu Linux. The video below shows the FM receiver listening on the local APRS frequency.

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Simple SSB transmitter using complex bandpass filter

There are several ways to generate a single side band signal in a software radio and I am slowly exploring each and every one of them. For this first attempt I have decided to try using a basic amplitude modulation followed by a bandpass filter with complex taps that can select either the upper or the lower side bands.

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Dynamic File Names in GNU Radio Companion

I needed a quick USRP IQ data recorder today to record the APT downlink from NOAA satellites. This is really trivial to implement using the GNU Radio Companion, but I had to figure out how to use dynamic filenames to avoid overwriting previously recorded data. Of course, I could just rename each file when recording has finished but I am too lazy to do things like that. Using the current date and time in the file name seemed to be a good solution.

This quick how-to explains how to use the Python datetime module to generate a unique filename in GRC.

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Binaural CW Receiver with GNU Radio and USRP

Today I felt like doing an experiment that is not quite on my TODO list – a binaural CW receiver. A binaural CW receiver is a receiver that gives a spatial feeling while you are tuning. As I understand it, you have to use stereo where the signals move from one side to the other as you tune and are in the middle when you are tuned to the frequency.

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Improved AGC for the simple SSB receiver

Few days ago I wrote about how I upgraded the simple double side band receiver implemented in the GNU Radio Companion to a simple single side band receiver. This initial implementation used some default values for the AGC attack and decay rates. These values were acceptable; however, I wanted to spend some time trying to find better values that would correspond to Fast, Medium and Slow AGC – just as we are used to in commercial radios.

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