Hello! I am experimenting with an old Primestar DBS dish and GNU Radio using the USRP and the DBSRX daughterboard. In order to power the dish's LNB, I need to send 12 volts up the antenna line. After reading previous posts to the GNU Radio mailing list about antenna bias and the DBSRX, I decided against a bias tee and applied 12 volts at 300 mA to the J100 jumper on the DBSRX.
When I hooked everything up indoors, I measured 12 volts, as expected, at the LNB end of the coax. Thinking all was well, I disconnected everything and moved the whole setup outdoors to start experimenting. However, after reconnecting everything, I now measured only 5 volts at the LNB end of the coax. Working backwards, I measured 12 volts at the J100 pins and 5 volts downstream. I recalled from previous posts that shorting J101 would give 5 volts from the USRP power supply. To be certain that this wasn't happening in this case, I disconnected the 12 volt supply and measured no voltage on the line. Reconnecting the 12 volt supply to J100 restored 5 volts to the line. I saw a reference in a previous post that, with the 5 volts in place from jumping J101, the DBSRX could not withstand a short at the SMA connector. According to the post, a small inductor acting as a fuse would be fried but could be replaced. Of course my first suspicion is that I caused this, maybe by an accidental short across the coax while measuring the voltage or connecting to the LNB. However, the fact that I'm still getting 5 volts as opposed to no voltage, like with a blown fuse, makes me wonder. I would greatly appreciate any insight or suggestions for additional diagnostics that you might have. Thanks in advance. Jon Jennings _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio