DAB tests with Basic TX
Test with the BasicTX: On the picture you see the board installed inside the USRP, TX A port (Upper right) This board take the signal from the DA's and provide the output with SMA connectors via a transformer. The don't use any actives components, you get after the transformer what you have directly from the DA. When we generate a signal on this board we have measured a total power of 18 uW. (with 50 ohm load 0 dB of gain in the gnuradio module)
As we use one DA from the TX A port (USRP have two DA's with balanced output on each port) we get a real signal at the output, meaning that you get every harmonics and image frequency till they go in the noise floor (bandwidth of the onboard transformer used to unbalance and adapt the output inpedance)
This is typically how looks the output spectrum of the BasicTX. Note the red marker showing the desired working frequency in the Band III (see Band 3 Channels) (exact value: 12C @227.360 Mhz during the measurement). To filter the lower and stronger peaks will required more than 80 dB of attenuation and the same for the next upper peak ! The picture show the spectrum from 0 to 750 Mhz
So ! this will required further filtering before applying any pre amplifier stage...
The same now but with a first filtering trial... we still have to much unwanted carriers near the working band !!! TBC...