The digital radio is one of the most commonly used telephone and data transmission system. It is used to link telephone exchanges and to provide links between GSM stations, i.e (BTS, BSC and MSC). When the terrain is rough or stations are inaccessible, the digital radio is the most preferred transmission mode.

In this experiment, we use the AT & T Digital Radio 6/11-40-140 which is designed to operate at two locations as follows.  

(a) A terminal station which originates and terminates voice or data traffic  

(b) A repeater station which receives, regenerates and retransmits signals along the radio transmission path.


The various components that constitute the radio system are mounted on the frames. A terminating station consisting of a line terminating frame and a radio frame. A repeater station consists of a two radio frames and a regeneration frame. Frame is used, in this case, to denote physical compartments used to mount various electronic equipment. Figure 1 shows the organisation of the AT&T Digital radio system.

The details of the layout of each type of frame are available here in pdf.

Figure 1. Organisation of the AT & T 6/11 Digital Radio System

On each frame, there are mounted various plug-in units as follows:
(a) Digital terminal shelf consists of a receive and transmit modules. The receive modules receives the IF signal from the radio receiver, demodulates the signal and converts back to original form. The transmit module gets the signal from the multiplexer, modulates the signal and sends it to the transmitter.
(b) Service Channel Shelf is located on the regenerator frame. Its function is to carry out performance monitoring, service channel switching, signalling and to issue alarms.
(c) Control and protection transmitting shelf is located on the line terminal frame. Its functions are to monitor the signal and provide protection.
(d) Digital Regenerator Shelf is located on the digital regenerator frame. Its function is to receive the IF signal from the radio receiver; demodulate it; restore signal level; and remove distortions. The signal is then modulated and retransmitted.
(f) Transmitter shelf is located on the radio frames. Depending on the number of channels, there can be up to 4 transmitter shelves. It receives the IF signal from the digital terminal trasmitter or digital regenerator and converts it into an RF signal. Figure 2 and 3  show various components of the tranmitter and the physical layout of the transmitter shelf.

Figure 2. 11 GHz Radio Transmitter

Figure 3. 6 GHz Transmitter Shelf

(g) Radio Receiver Shelves are located on the radio frame. There can be up to 4 radio receivers depending on the number of channels used. It receives RF signal and converts it to Intermediate Frequency (RF) signal. The IF is then sent to the digital regenerator or the digital terminal receiver. Figure 4 and 5 show various components of 11 GHz radio receiver and the layout of the receiver shelf.

Figure 4. 11 GHz Radio Receiver

Figure 5. 11 GHz Receiver Shelf


1. Power up two terminal stations and check their status by refering to the following

     (a) The controls, jacks and indicator manual (found here in pdf)

     (b) The Alarm Matrices manuals (found here in pdf)

     Summarize your status findings in your report.

2. With assistance from the Lab technician, connect the radio system for 6-GHz or 11 GHz radio line-up. With the aid of a diagram, describe the process of carrying up the selected line-up.

3. Identify  and locate, on relative basis, all radio channels assigned to the transmitter and receiver.

4. Using a spectrum analyser,

     (a) display IF spectrum profiles for channels 1-8. Draw the profile in your lab report.

     (b) Display the IF spectrum of one selected channel with all adjacent channels present. Draw the profile in your lab report.

4. Analyse your results with specific reference to telecommunication transmission theory learnt in class



AT&T digital Radio Manuals





Prof. Ambani Kulubi May-Aug 2015