Most wireless transmitters require high towers to get the coverage area. These are often out of town so the problem is to get the downstream signal from the Internet point of presence to the transmitter. This path is as important as the rest of the system and must be properly designed. There are two basic transmission media, wireless and fiber optics, and two transmission technologies, amplitude modulation and frequency modulation. Amplitude modulation offers more channels. The choice depends, however, on whether there are existing links for television signals and how far it is possible to plan ahead as the business grows.

	Amplitude Modulation	Frequency Modulation
wireless	amplitude-modulated link (AML) to 31 channels	amplitude-modulated link (AML) to 31 channels
precautions	Noise filter may be needed.	downconvert from 44 MHz to baseband, noise filter used
fiber optics	standard CATV fiber optics link 36 to > 69 channels	frequency modulation (FM) fiber link 1 to 16 channels, obsolescent
precautions	standard	downconvert from 44 MHz to baseband, noise filter used

Table 3. A Choice of Uplink Types

It is important to note that in a wireless environment, frequency drift in the uplink degrades the stability of the final transmitted downstream signal. In the STL case, the downconverters and upconverters convert the 44-MHz IF signal to near the baseband stability. In the case of amplitude-modulated links, the conversion to the CATV band and back to IF degrades stability unless the devices can be locked to a stable reference.