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 _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
