Connecting a receiver to the DBSRX

Hi All,

I’m about to connect another receiver to the DBSRX to see the spectrum.

Q1: can I break sumthing if connect it straight (receiver -> DBSRX)
Q2: should I use an attenuator (ex: TV 0…20 dB)

Patrik

Hi All,
I’m about to connect another receiver to the DBSRX to see the spectrum.
Q1: can I break sumthing if connect it straight (receiver -> DBSRX)
Q2: should I use an attenuator (ex: TV 0…20 dB)
Patrik
What kind of receiver is it, how much gain, and what is its maximum
output level?

The DBSRX has a GaAs LNA on the front-end, which doesn’t really like
signals above -10dBm, I would put in at least 30dB, depending on
what the signal source is. The DBSRX (and DBSRX2) are both capable
of “seeing” signals down to below -120dBm all by themselves, so
if you’re using them as “IF processors” for high-frequency receivers,
put in a fair amount of attenuation. Even without the hazard of
damaging the LNA, you don’t want to end up in non-linear territory
because of too-high levels going into the receiver card.

With the exception of the BASIC_RX and LF_RX, all of the Ettus receivers
are generally designed for “off air” reception, connected
to an antenna. So if you’re using them as the “IF”, you should
definitely attenuate the input levels down quite a bit.

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

From: [email protected]valid
[mailto:[email protected]valid] On Behalf Of
Marcus D. Leech
Sent: Thursday, 10 November 2011 2:15 PM
To: [email protected]
Subject: Re: [Discuss-gnuradio] Connecting a receiver to the DBSRX

Hi All,

I’m about to connect another receiver to the DBSRX to see the spectrum.

Q1: can I break sumthing if connect it straight (receiver -> DBSRX)

Q2: should I use an attenuator (ex: TV 0…20 dB)

Patrik

What kind of receiver is it, how much gain, and what is its maximum
output
level?

The DBSRX has a GaAs LNA on the front-end, which doesn’t really like
signals
above -10dBm, I would put in at least 30dB, depending on
what the signal source is. The DBSRX (and DBSRX2) are both capable of
“seeing” signals down to below -120dBm all by themselves, so
if you’re using them as “IF processors” for high-frequency receivers,
put
in a fair amount of attenuation. Even without the hazard of
damaging the LNA, you don’t want to end up in non-linear territory
because
of too-high levels going into the receiver card.

With the exception of the BASIC_RX and LF_RX, all of the Ettus receivers
are
generally designed for “off air” reception, connected
to an antenna. So if you’re using them as the “IF”, you should
definitely
attenuate the input levels down quite a bit.

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.

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.

Some images of the test setup @
http://www.poes-weather.com/~patrik/usrp/dvb-dbsrx/

Thanks to all for the help,
Patrik
----- Original Message -----
From: Marcus D. Leech
To: [email protected]
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 L.
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

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