ET-A Microwave Communication System

The ET-A mircowave communication system provides a complete long-haul microwave network in the European area. The system consists of two basic types of site configurations, mainline sites and tributary sites.

(1) Mainline Sites: these are sites along the primary broadband multichannel radio network.

(2) Tributary Sites: these are remote stations requiring only single- or two-channel special purpose communications.

Mainline Sites. The mainline sites form important links in the primary radio network. Much of the radio equipment used at mainline sites contains cabling for future equipment additions. Since traffic loads and site functions differ along the mainline route of communication, the size and complexity of the sites vary considerably. Mainline sites may vary in size from an ordinary repeater station to a fully implemented nodal point station or console site (see Mainline Site Configurations below).

Tributary Sites. Tributary sites are remote stations which are serviced by the mainline of the ET-A system. Tributary sites are connected to the mainline through nodal point sites.

ET-A Console System. The ET-A Console System is a command and control facility incorporated within the ET-A microwave communication system. It uses the radio and multiplex equipment of the ET-A microwave communication system to provide semi-automatic conference call capabilities between the local telephone sets (drop subsets) at various headquarters locations (Console Operations Centers) and a large number of military installations (tributary sites). Basically, the Console System consists of six Console Operations Center sites and a number of Console Remote Equipment (CRE) vans. A Console Operations Center is linked to a CRE van via the radio and multiplex equipment along the mainline. (Five mainline "command and control" channels are used for this purpose.) The CRE vans are located at the mainline nodal sites, each van being equipped to service a maximum of 24 tributary sites.

MAINLINE SITE CONFIGURATIONS

1. General
a. The equipment complements at mainline sites vary and depend on the operational requirements of each specific mainline site. However, all mainline sites fully or partially fall into one of the following six basic configurations:
Through repeater site
Drop repeater site
Terminal Site
Junction Site
Nodal point site
Console site

The six configurations are discussed in paragraph 3 through 8.

b. In addition to basic configuration variations, the radio equipment complement varies due to different microwave transmission modes. Mode variations are described in paragraph 2.

2. Diversity and Modes of Operation
The sites on the mainline broadband network of the ET-A system use the troposcatter, diffraction or line-of-site mode of microwave transmission; four-fold or two-fold space diversity configurations are utilized.

a. Troposcatter. In the troposcatter mode of operation the radio equipment required to meet system performance requirements consists of either 1-kw or 10-kw transmitters, receivers with or without parametric amplifiers and treshold extension, 15 or 30-foot antennas, and four-fold space diversity. The four-fold space diversity configuration uses two antennas, two transmitters, and four receivers (two dual receivers).

b. Diffraction. In the diffraction mode of operation the radio equipment required to meet system peformance requirements consists of 1-kw transmitters, receivers with parametric amplifiers and threshold extension, 30-foot antennas, and four-fold space diversity (see a above). Only one mainline link (Site 11.1, Feldberg/Schwarzwald, to Site 46, Savona, Italy) operates in this mode.

c. Line-of-Sight. In the line-of-site (LOS) mode of operation the radio equipment required to meet system performance requirements consists of 1-watt transmitters, receivers without parametric amplifiers and treshold extension, 4 or 6-foot antennas, and two-fold space diversity. The two-fold space diversity configuration uses two antennas, two transmitters, and two receivers.

3. Through Repeater Site
a. The through repeater site is usually located in a high-elevation area for the purpose of linking two mainline sites between which direct communication in the troposcatter mode is not feasible. The through repeater receives the microwave signal from one site, amplifies it, and transmits it to the next site. A block diagram of a through repeater site is shown in figure 2.

b. The through repeater site equipment complement consist of two radio shelters, each of which is connected to an antenna system and a maintenance control center (MCC) console. The antenna systems are pointed toward the neighboring mainline site antenna system, while the radio shelters are connected back-to-back at the multiplex baseline level. The orderwire channel from each direction is dropped to voice frequency in its corresponding radio shelter and extended to the MCC. In each radio shelter, only the orderwire channel in the direction of the shelter's shoot may be utilized. At the MCC, however, the orderwire channels may be utilized in either direction, or may be connected as a through circuit in both directions for conference purposes. Summary fault alarm circuits are extended from both radio equipment shelters to the MCC, permitting monitoring of the equipment from one location and eliminating the requirement that personnel be in the radio equipment shelter continually.

4. Drop Repeater Site
a. The purpose of the drop repeater site is to divert a limited number of multiplex channels from the microwave signal for local use. A block diagram of a drop repeater site is shown in figure 3.

b. The drop repeater site equipment complement consists of two radio equipment shelters, a multiplexer set, and a maintenance control center console. The antenna systems are pointed toward the neighboring mainline site antenna system. Each radio equipment shelter feeds its multiplex baseband output to the multiplexer set. The multiplexer set processes the baseband from one direction, dropping a limited number of channels to voice frequency level for local subscriber use. The remaining channels are passed to the other baseband, at either channel, group, or supergroup level, for transmission to the next site.

c. Orderwire channels from each direction are dropped to voice frequency in the radio equipment shelter and extended to the MCC. Each radio shelter may use the orderwire channel in the direction of the shelter's shoot only. However, at the MCC the orderwire channels may be used in either direction or may be connected as a through circuit in both directions for conference purposes. The MCC also extends a local orderwire circuit to the multiplexer set, which can also be connected into the conference circuit.

d. Summary fault alarm circuits are extended from both radio equipment shelters and the multiplexer set to the MCC, permitting monitoring of the site equipment at the MCC without requiring personnel be in the radio equipment and multiplexer set shelters continually.

5. Terminal Site
a. Terminal sites are located at each end point of the ET-A mainline, where all multiplex channels are dropped for local subscriber use or interface with other systems. A block diagram of a terminal site is shown in figure 4.

b. The terminal site equipment complement consists of either one or two radio equipment shelters, a multiplexer set, and a maintenance control center console. The terminal site shown in figure 4 utilizes one radio equipment shelter.

c. The radio equipment shelter is connected to an antenna system which is pointed toward the next site on the mainline. From the radio equipment shelter the baseband is fed to the multiplexer set, where all channels are dropped to either supergroup, group, or channel level for either local subscriber use or interface with other systems.

d. Orderwire channels and summary fault alarm circuits are utilized as described in paragraphs 4c and 4d, respectively.

6. Junction Site
a. A junction site serves as a junction for the mainline paths converging on the junction from three or more directions (sites). A junction site block diagram is shown in figure 5.

b. The junction site equipment complement consists of a technical control van, two or more multiplexer sets, three or more radio equipment shelters, and a maintenance control center console.

c. The junction site shown in figure 5 utilizes two multiplexer sets and three radio equipment shelters. Each radio equipment shelter is connected to its antenna system, which is pointed toward another site; thus three paths are converging on the junction site. Radio equipment shelters RS A and RS B feed their baseband outputs to multiplexer set MS A, while radio equipment shelter RS C feeds its baseband to multiplexer set MS B. The mulitplexer sets drop the three basebands down to channel voice frequency level. All channels are then routed to the technical control van. The technical control van contains a main distributing frame for cross-connecting the voice-frequency channels, in any of the three radio-frequency directions, to other systems or to local subscribers. Jack fields are also provided for patching or monitoring all channels.

d. Orderwire channels and summary fault alarm circuits are utilized as described in paragraphs 4c and 4d, respectively.

6. Nodal Point Site
a. A nodal point site serves as a junction for connecting the tributary sites to the mainline communications network. A nodal point site block diagram is shown in figure 6.

b. The nodal point site equipment complement consists of one to three nodal point radio sets, one Console Remote Equipment van, a multiplexer set, and one (terminal) or two (repeater) radio equipment shelters.

c. The nodal point site shown in figure 6 utilizes one nodal radio and two radio equipment shelters. The two radio equipment shelters and the mulitplexer set are set up as a through repeater site, as described in paragraph 3. The multiplexer set drops five command and control multiplex channels (used throughout the ET-A Console System) to voice-frequency level and feeds them to the CRE van.

d. The CRE van can service as many as three sectors of up to eight tributaries each, a nodal point radio set being required for each sector. Therefore, as many as three nodal point radio sets can be connected to the CRE van. Operation of the CRE van is automatic and is controlled by signals from either a Console (site,) Operations Center or a tributary site. The command and control channels () carry controlling signals and traffic from the console sites and other tributaries. The five channels from each direction of the mainline are bridged in the CRE van, thus giving the switching circuits of the CRE van uninterrupted connection to the mainline in both directions. From the CRE van one transmit oderwire, one transmit carrier channel, and eight receive channels are fed to the nodal point radio set, which feeds a pair of antennas pointing in the direction of a tributary site. Eight tributary sites can be so connected by eight antenna pairs.

e. The CRE van, on receiving a command from a Console Operations Center (to) a tributary site on one of the command and control channels, connects that channel of the transmit channels to the nodal point radio set. The nodal point radio set then transmits the data to all equipped tributaries. Traffic from a tributary is sent to the nodal point radio set and then to the CRE van on the tributary receive channel (??) to that tributary. The CRE van connects the traffic received from the tributary (to one) of the command and control channels for transmission, via the mulitplexer set () radio equipment shelter, to the other tributary or to the Console Operations Center.

f. Orderwire operation at the radio equipment shelters and multiplexer is the same as described in paragraph 4c. Service is also extended from the MCC to the CRE van and the nodal point radio set. Select controls are provided at the (CRE) and nodal point radio set for selecting the orderwire channel to any one of the (eight) tributaries. The MCC van can also connect the mainline orderwire with the tributary orderwire.

g. Summary fault alarm circuits are extended from all shelters and vans to the MCC, thus permitting monitoring of the equipment at the MCC without requiring personnel to be at the shelters and vans continuously.

7. Console Site
a. The console site provides central control capability within the command and control network of the ET-A system. A block diagram of a console site is shown in figure 7.

b. The console site equipment complement consists of a Console Local Equipment van, an Operations Center (in building or van), a multiplexer set, one or two radio equipment shelters, a maintenance control center, and telephone drop subsets.

c. The Console Operations Center equipment (which includes the Operations Center and CLE van) may be used with the drop repeater configuration or the terminal configuration. The block diagram shown in figure 7 utilizes the terminal configuration. From the multiplexer set the five multiplex voice frequency channels, which are assigned command and control channels in the ET-A Console System, are routed to the CLE van for processing.

d. The CLE van contains the logic and signaling circuitry that performs the following functions:

e. The orderwire operation is the same as described in paragraph 5, with service also extended to the CLE van.

f. Summary fault alarm circuits are extended from all shelters and vans to the MCC, permitting monitoring of the console site equipment from one point.

"C" Det, EGSM Company, was located at Nelson Barracks, Neu Ulm, in the early 1970s. They provided signal support for microwave and other signal sites in southern Germany.