Re: [Discuss-gnuradio] tvrx lna questions

[Matt Ettus]

Engin Karabulut wrote:
> hi all,
> I have usrp and tvrx daughterboard,but tvrx sensitivity
> is very bad, minimum input signal level is 40 dBuV(equal to-68dBm).
> and noise figure is 8-10 dB. even if you have hi gain antenna, weak 
> signals die in TVRX. then I decided to purchase LNA next to antenna.
> LNA that I chose is minicircuit's ZX60-33LN+.

The noise figure is 8-10 dB.  However, it is meaningless to say that the 
minimum input signal level is -68dBm.  Sensitivity numbers only have 
meaning if you also specify a modulation system, bandwidth, and error 
rate.  -68dBm would be very bad for AM radio, but would be perfectly 
reasonable for 802.11n.

There's no reason you couldn't receive a signal at -200dBm on any 
receiver, as long as the bandwidth was low enough, and you filtered 
narrowly enough.

Also, are you sure you are controlling the gain properly?

> http://www.minicircuits.com/pdfs/ZX60-33LN+.pdf
>
> If I use this LNA,can I receive weak signals(like -100dBm)?

That LNA has a noise figure around 1 dB.  If everything else remained 
the same, you could receive a signal which was about 6 or 7dB weaker 
than without the LNA.

Matt