MMDS 2.3 GHz


Point-Point and Point-Multipoint

1. System Description

A point – multipoint (and point to point) microwave distribution system (MMDS or AM micro) designed for the transmission of several TV program signals in the microwave band. The AM-VSB modulated TV signals together with the FM modulated pertaining voice channels are lined up in 8 MHz channels.

The typical construction of the 2.3 GHz system manufactured by our partner in Hungary is shown in Fig.1. The programs arriving from several different locations can be transferred from the base band either in the VHF or the UHF bands into the neighboring channels with the aid of channels units (modulators). In this case the channels are mixed up into the VHF band on the unique modulator outputs and a combiner takes them to a distribution amplifier. The output level range of the distribution amplifier is approximately the same as the output level of the modulators ( 90 – 110 dBμV at 75 Ω ). 

In the MDS 230/T MDS transmitter the VHF channels are up-converted into the 2.3 GHz microwave band and amplified to the necessary level. It is important that the adding of the transmitter’s own noise to the noise balance should be low enough together with the intermodulation products caused by the simultaneously transmitted channels located closely on each other.

In order to cover an area the output signals of the transmitters must be distributed to the antenna system. A typical example is shown in the microwave distribution network in Fig.2. where 3 dB hybrids can divide the output signal of the transmitter into 8 parts. After the division the new levels on each output port have to be amplified in order to give the necessary level for each antenna required by the MMDS system. In the same example, the 3.5 dB real attenuation of the individual microwave hybrids will result about 10.5 – 11 dB total attenuation plus the added attenuation of the connecting cables. In order to reach the desired level a microwave output amplifier block must be attached to each output with the same requirements as valid for the amplifiers of the transmitter (low own noise and high linearity).  








2. Technical data

Input frequency level                 198 – 238              GH
Input level range 
1 TV channel                  90 – 110              dBμV / 75Ω

5 TV channels                5 x 90 – 110           dBμV / 75Ω
Input impedance                       75                          Ω
Output frequency band              2290 – 2335                   MHz (optional)
Output level (1 TV channel)        40                          mW
Output level (5 TV channels)      5 x 40                     mW
Output impedance                    50                          Ω
Output connector                     “N-“
TV channel RF signal/noise
(C/N)                                        min. 63                dB
Output IP3                                55                          dBm
Output IM3 (at nominal
output levels)                            min. 60                dBm
Out – of – band components’

         level compared to the
         carrier                             max. – 70             dBc
Consumption figures
Mixer and preamplifier               150                        W
End amplifier                            150                        W
from 220 V AC                          max. 2                  A
Temperature range                    0 - +50              ºC
Storage                                   -35 - +65              ºC

  Note: The manufacturer reserves the right to change the data without notice.

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