Re: [Discuss-gnuradio] USRP2 Transmit Power

[Marcus D. Leech]

On 08/06/2010 02:32 PM, Sylvain Munaut wrote:
>
> You are connection the output of one RFX _directly_ to the input of
> another one ??? Without attenuators ?
>
> that doesn't sound wise.
>
>
> Cheers,
>
>     Sylvain
>
>
>   
Indeed, the LNA in the receive chain on many of the boards will have a
hard time
  coping (device damage possible) with anything greater than roughly
0dBm, although the
  MGA82563 lists an absolute maximum input power of +13dBm, you'll get
nasty clipping long
  before then, and it wouldn't surprise me if you'd end up blowing-out
the mixer.  Which is why
  Matt generally recommends no more than -10dBm into the front end of
the Rx boards.  And really,
  for a general-purpose receiver, a -10dBm signal is what we technically
call "thunderin' loud".

The Rx side of most boards includes an LNA, and the intention is that
they be used as off-air
  receivers, which means that they "expect" a fairly low-level signal. 
Connecting the Tx side
  directly to an Rx is a way to potentially have the magic smoke come
out, or at least get quite
  undesirable non-linear responses from the receive chain.

For doing lab tests, with direct connections, a set of attenuators can
be your best friends:
  10dB, 15dB, 20dB, 30dB.   I'd use the 20dB *minimum* if I was
connecting the Tx side directly to the
  Rx side--that way, even with +17dBm "full power", the Rx would only
see -3dBm, which is still
  a lot, but it likely wouldn't damage anything.


-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org