The amplifier in an OCAR often doesn't need particularly low noise figure. This is because only the "top part" of the amplifier's output range is used. Most users won't hear the noise floor produced. This allows considerable latitude in the design and implementation of both the filtering and the amplifiers. Good linearity is of more importance than low noise, low loss and high sensitivity.

An exception to this would be when an OCAR is being used to provide "connectivity" to a weak signal environment; an OCAR used to connect all users to satellite transmit and receive antennas, for example. In this case, it is desirable that the noise floor presented at the receive antenna (proably a highly directional, tracking antenna) be delivered to each user.

In our 900 MHz OCAR, the amplification is distributed across three different enclosures.

1. an input (preamplifier) stage, two MSA-06 MMICs with a ceramic bandpass filter (BPF) located at the receive antenna
2. an intermediate stage, a combination of discrete and integrated gain blocks, with power distribution located on the coax in between the antennas
3. output (power) amplifier stage, Mitsubishi FM PA-driver "brick" rebiased for linear operation, located at the transmit antenna

DC power to the two antenna mounted gain stages is distributed by the same coaxial cable which connects them for RF signals. By separating the stages in this manner, no special packaging techniques are required to get large amounts of gain along with stability. All amplifiers are mounted in plastic food containers (Tupperware) to keep water out.

OCAR Amplifier Responses

• 900 MHz OCAR Amplifiers
• Individual Amplifier Responses
• Combined Response

The total amplifier gain is about 85 dB. Because there is several dB of cable+input_filter loss, the final gain of ~79 dB is actually a little low of what is desired and we plan to replace the first amplifier with one which can provides up to 10 dB more gain.