13 GHz SYSTEMS DESCRIPTION

The microwave input signal passes through the ferrite attenuator and into a low-noise amplifier (LNA). The signal then passes through the image reject filter and into a ferrite isolator and then into the mixer where conversion to VHF occurs. The output of the mixer is amplified by a low-noise VHF preamplifier, whose output is connected to a VHF automatic gain control (AGC) module. The signal then passes through a 3 dB pad to the AC/VHF diplexer. The VHF output of the diplexer is connected to the 5/8-24 cable entry (output of the receiver).

Local oscillator power for conversion of microwave to VHF is provided by the solid-state source to the mixer by means of a semirigid coaxial cable and isolator. The source is indirectly phase locked to a harmonic of the 74-MHz pilot tone signal that is tapped off the VHF AGC module. The pilot tone filter rejects all the VHF signals with the exception of the pilot tone, which is then amplified in the AGC amplifier. This unit maintains the pilot tone signal at a constant level at its output. The phase detector compares the phase of the pilot tone to that of the voltage-controlled crystal oscillator (VCXO). From this phase comparison, a dc voltage is generated and fed to the VCXO to control its frequency. The solid-state source is in turn phase locked to an additional output of the VCXO.

The pilot tone signal is also used in the microwave AGC loop. The pilot tone is extracted at J12 before it goes through any AGC stages of the AGC amplifier. (The name of this amplifier refers to the AGC function it serves in the phase lock loop, and to neither the microwave nor the VHF AGC.) The pilot tone is fed to the ferrite driver, where it is detected and used to control the amount of attenuation set into the ferrite attenuator.


18 GHz AML SYSTEM DESCRIPTION

18 GHz AML (Amplitude Modulated Link) Transmission Systems are point-to-point wireless trunking systems operating in the 18.1-18.6 [GHz] (Private Cable) band which are used to extend the reach of a cable plant or MMDS cells that distribute broadband analog and/or digital signals.

In many applications there are economical, geographical, or regulatory restrictions which make AML systems more attractive link solutions than hybrid fiber coaxial (HFC) alternatives, particularly in the light of implementation budgets and schedules.

The fundamental building blocks of a Microwave AML Transmission System are Transmitters, Repeaters, and Receivers.

All 18 GHz AML Wireless Networks Receivers are outdoor units mounted in close proximity of the associated antenna. Outdoor units are optionally supplied with hardware kits for mounting on free standing or wall supported 4.5" diameter steel pipes.

Antennas and ancillary associated hardware can also be specified and supplied by AML Wireless Networks.

To facilitate the use of 18 GHz AML systems as cable plant extenders, Transmitters are designed to directly accept standard CATV channel signal levels with bandwidth up 72 NTSC analog video channels.

AML Transmitters translate entire CATV channel line-ups to a microwave frequency and AML Receivers downconvert the microwave signals to provide a spectral replica of the channel line-up injected at the input of the microwave Transmitter, in full compatibility with the ensuing cable plant.

AML Wireless Networks provides ultralinear systems with very low inherent phase noise which makes them ready to handle high level digital modulation schemes. AML systems can transport mixed analog and digital traffic, either from telephony or from MPEG-1 / MPEG-2 digital video compression sources with any degree of channel compression.