[USRP-users] Input power limit for B2x0 series

Sivan Toledo stoledo at tau.ac.il
Sat Jul 8 04:03:27 EDT 2017


Hi, I am trying to understand the input-port limit of the B2X0 series,
which is specified as -15dBm in the User's Manual (
http://files.ettus.com/manual/page_usrp_b200.html).

The issue is that if I use external front-end components (masthead LNA and
a saw filter), it is difficult to limit power to -15dBm (limiting to a 0 or
single-digit dBm is possible with common limiters).

Is the -15dBm the limit that will cause overload and distortion even on the
lowest gain setting, or is it a safely limit above which the unit may get
damanged?

Looking at the schematics of the B210, the input if fed to a switch that
can sustain almost 1W, then through something that looks like a limiter
(U800 and U813), then through another switch, and then to the inputs of the
AD9361, which can tolerate up to 2.5dBm. So it's hard to see why anything
up to 2.5dBm will damage the B2x0, and assuming that U800 and U813 do have
some useful limiting function, maybe much more is safe.

Can you please clarify? I am considering using B2x0 for an application that
may subject them to about 3dBm, maybe 3.5dBm (we use an LNA, followed by a
6dBm-max limiter, then a SAW filter with an insertion loss around 3dB), and
I want to make sure that this is safe.

Thanks, Sivan Toledo
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