As you may know, between January 14 and February 18 I have been away from home on a research expedition to Antarctica. Several people have asked me for a post detailing my experiences, and I was also thinking to write at least something about the trip. I could spend pages talking about the amazing landscapes and fauna, or daily life in Antarctica. However, in keeping with the spirit of this blog, I will concentrate on the radio related aspects of the trip (and there are indeed enough to tell a story). If I see that there is much interest in other topics, I might be persuaded to run a Q&A post or something similar.
Apparently, my trip and my posts in Twitter raised the attention of a few Hungarian Amateurs, who even discussed and followed my adventures in their Google group. Thanks to Janos Tolgyesi HG5APZ for his interest and for some good discussion over email during my voyage.
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I have a DF9NP 10MHz GPSDO that is based on a u-blox LEA-5S GPS receiver. Essentially, the LEA-5S outputs an 800Hz signal that is used to discipline a 10MHz VCTCXO with a PLL. The LEA-5S doesn’t have persistent storage, so an I2C EEPROM is use to store the settings across reboots.
Lately it seemed that the reading of the settings from the EEPROM had failed. The u-blox was always booting with the default settings. This prevents the GPSDO from working, since the default for the timepulse signal is 1Hz instead of 800Hz. Here is the summary of my troubleshooting session and the weird repair that I did.
Continue reading “Weird repair of the day: u-blox LEA-5S I2C interface”
Last week I published my results about the LilacSat-2 VLBI experiment. There, I mentioned that there were some things I still wanted to do, such as studying the biases in the calculations or trying to improve the signal processing. Since then, I have continued working on this and I have tried out some ideas I had. These have given good results. For instance, I have been able to reduce the delta-range measurement noise from around 700m to 300m. Here I present the improvements I have made. Reading the previous post before this one is highly recommended. The calculations of this post were performed in this Jupyter notebook.
Continue reading “Improved signal processing for LilacSat-2 VLBI”
On 23 February, Wei Mingchuan BG2BHC published on Twitter the first Amateur VLBI experiment. This consisted of a GPS-synchronized recording of signals from LilacSat-2 using USRPs in groundstations at Harbin and Chongqing, which are about 2500km apart. Wei has made a Github repository containing the recording (in MATLAB file format) and some signal processing in MATLAB. I have done some signal processing of my own with the recording and published my results in a Jupyter notebook. Here I describe some general aspects about VLBI and its use in Amateur radio, and some specific details of the signal processing I have done.
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Many Amateur radio operators are familiar with the effects of the ionosphere at HF frequencies. However, the effects of the ionosphere are also noticeable at much higher frequencies. In particular, at L band, which is used by most satellite navigation systems. Thus, GNSS receivers can be used to measure ionospheric parameters. These measurements are usually distributed as TEC maps in IONEX files.
Here I describe some basic ionospheric physics, how a GNSS receiver can measure the ionosphere, and give some Python code to study TEC maps in IONEX files. Then I use TEC maps to study the CODAR ionospheric observations I did in December last year.
Continue reading “Studying IONEX files”