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I added 3 x 20 dB attenuators before entering DBSRX. It
works as I imagined and I didn't fry the daughtercard.
I could verify that I master the si2109
demodulator.
Thanks to all for the help,
Patrik
----- Original Message -----
Sent: Thursday, November 10, 2011
6:02
Subject: Re: [Discuss-gnuradio]
Connecting a receiver to the DBSRX
To my understanding, the DBSTX is designed for Satellite TV reception. So it should be safe to connect the output of the satellite LNB to the DBSRX without problem. In fact, I tried to connect the LNB out port of a DVB-S set top box to the DBSRX directly without problem or distortion. KZ
The
only difference is that the DBSRX/DBSRX2 has an extra 20dB gain stage ahead of
the DBS downconverter chip. In most set-top-box
situations
there wouldn't be that extra 20dB of gain. So yes, the downconverter
*chip* is designed to hook up directly to an LNB/LNBF,
but the DBSRX
family have an extra stage of low-noise gain to allow direct connection to an
L-band antenna for L-band "off air" work
(and for things like radio
astronomy and amateur satellite work, etc, etc).
Padding with an
attenuator can't hurt in this case, and in *some* cases, can save the
DBSRX/DBSRX2 from damage coming from things like
C-band radar pulses
getting downconverted by the LNB and potentially producing damaging signal
levels at the DBSRX/DBSRX2. LNBs
generally have very high gain
(50-60dB is typical), which means that for "ordinary, expected" signal levels
of roughly -120dBm or lower,
the LNB converts to levels that are
"comfortable" for DBS receivers/receiver chips. But on C-band, you have
C-band radar to worry
about sometimes, which can produce
very-high-level transients.
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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