Transmit gain

I am using the example to transmit using the Basic TX
daughterboards. I am getting about a 30mV peak-to-peak signal and I
want to know if I can add more gain to the signal. I don’t know alot
about this stuff. I was thinking it might have to do with the line that

gain = gr.multiply_const_cc (4000.0 / options.nchannels)

but I don’t know how much gain I can give it (if I just increase the
number 4000 or if this is not the way to do it). Any help would be much