[USRP-users] Input power limit for B2x0 series

Dan CaJacob dan.cajacob at gmail.com
Sun Jul 9 00:11:25 EDT 2017


I think (having gone through this before) that the real badness happens if
you put -15 dBm in the front end *and* turn all the gain up to the maximum.
Then some chip in the chain goes over its limit.

Really though, with a real world system, over the air, I'd be shocked if
you could blow up the front end. What you have to be careful about is when
you cable it directly to a transmitter. Even USRP to USRP, I always use at
least 30 dB of attenuation and preferably 60 dB, just to be safe.

On Sat, Jul 8, 2017 at 4:04 AM Sivan Toledo via USRP-users <
usrp-users at lists.ettus.com> wrote:

> 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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> USRP-users at lists.ettus.com
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>
-- 
Very Respectfully,

Dan CaJacob
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