Rayzer, There are clear and limited definitions, unlikely to be changed, for what legally constitutes a "radio" or a "transmitter". The "mistake" of the SDR manufacturers was to ever call or market them anything but instruments (as Red Pitya has done). When the idea of classifying them as instruments was floated in the early days of the GnuRadio list (by Steve Schear) he cautioned to make sure the products weren't called anything that might even vaguely sound like a wireless device. Evidently the marketing people at these companies knew better. End-user controlled software signal generation and capture techniques are now widely in use by premium instrument manufacturers. If the FCC attempts to curtail the frequencies, modulation types, etc. by these these test instruments I think there will be manufacturers screaming bloody murder. Transmitters are generally much simpler electronically than receivers (which are much less regulated). They may be little more than a few components added to a digital circuit, as Rayzer pointed out, though that rarely leads to a generally useful device. Attaching a circuit which contains the necessary components to generate the desired digital signal (e.g., using a Direct Digital Synthesizer) and convert it to a quality analog one to a USB or on a header of a PC/SoC motherboard should provide a nice signal generator which could effectively bypass FCC enforcement (legally or otherwise). WW