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Transmitting a simple sine wave in gnuradio using the USRP - and measuring it's power

Transmitting a sine wave with the USRP is a simple matter of connecting your USRP to the computer and running an equivalent gnuradio flowchart as displayed below.

The signal source is set to zero frequency with an amplitude of 1 - this serves as the baseband signal. The signal is then modulated by the UHD: USRP sink block with a center frequency set by the user. The center frequency represents the carrier frequency that up-converts the baseband signal. The gain is set to "normalized" with the maximum value of 1. This ensures that the USRP is always transmitting at it's highest power.  The reason for setting our baseband/signal source frequency to zero is that we only measure the actual output power of the USRP at it's center frequency, avoiding any modulation effects. 
Now that your script is ready, all you need is a transmission line/antenna to connect to one of the RF-channels of the USRP. Our setup looked like this:

The version seen on the picture is a USRP2 with…

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