To boost that -10 dBm tester as decribed in the documentation, you can buy an inexpensive RF amp on amazon, ebay, etc. See this page for details:
I bought two of the same design, but different layout. The square one did not sit flush onto the heat sink. Some grinding fixed that. The rectangular one did sit flush. Both performed almost the same. From 9-12 V, you'll get about 30 dB gain (or more), depending on input frequency. Of course, you'll also get lots of harmonics, so a LPF is needed.
These modules are sold as 2-3 W, but are really only good for 1 W, unless you want to burn it up. With 0 dBm input and the correct voltage, you'll get 1 W out (harmonics included). Also, my two modules worked up to 700 MHz, then the output fell off rapidly.
Here is a picture of the two that I bought:
