DBSRX and bias voltage issue

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

This forum is not affiliated to the Ruby language, Ruby on Rails framework, nor any Ruby applications discussed here.

| Privacy Policy | Terms of Service | Remote Ruby Jobs