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FM 24-18: Tactical Single-Channel Radio Communications Techniques

APPENDIX F
NET RADIO INTERFACE

Section I. Purpose and Scope

F-1. Purpose

NOTE: The term radio-wire integration (RWI) is being replaced by net radio interface (NRI). The functions and operations remain the same, but the name change more closely reflects the service provided.

This appendix provides information on the doctrine and operation of TOE net radio interface facilities installed in tactical areas. Procedures for operation of nontactical, garrison type administrative NRI facilities may be developed by local commanders. It provides commanders, operators, and users of NRI facilities the information needed to use this capability effectively in a tactical setting. It may also be used to help personnel prepare for command post exercises and field training exercises. It will be a valuable aid when used with a unit's Army training and evaluation program (ARTEP).

F-2. Scope

Section II of this appendix provides information on the doctrine and deployment of NRI. Section III provides information to both the switchboard operator and the NRI operator on installation and operation of an NRI facility. Section IV provides information regarding Radio Set Control C-6709 which is designed to provide NRI with the automatic switches.

Section II.
Doctrine and Deployment

F-3. Location of NRI

To carry out command and control responsibilities, a tactical unit commander must have all authorized means of communications readily available. The principal means of command and control are the tactical radio and telephone networks. Although each of these networks is a distinct, specialized means of communications, it is possible--and often required--to interconnect or interface them. This interface capability is provided by net radio interface equipment.

At corps level, a net radio interface station is located at--

  • Main.
  • Tactical command post.
  • Corps support command.
  • Area signal centers (ASC).

At corps level, NRI is installed and operated by the corps area signal battalion at each signal center. Commanders of all units serviced by the ASC are authorized to use the NRI facility.

At division level, a net radio interface station is located at--

  • Main.
  • Division support command.
  • ASCs.
  • Division artillery.

At division level, NRI is installed and operated by the division signal battalion. The NRI facility is available to the commanders of all units of the division.

F-4. Use of NRI

At corps level, NRI stations are used--

  • By the commanding officer, corps staff, and other designated key personnel in the corps.
  • For initial establishment of telephone service from the corps area communications system to using units.
  • To keep commanders and staffs in contact with subordinate and higher headquarters, as required, during the displacement of command posts (CP).
  • For emergency FM communication between elements in the corps area where there is a loss of telephone communications. At division level, NRI stations are normally used--
  • To establish emergency communications between mobile FM radio stations and elements connected to the division area telephone system by telephone.
  • To establish communications between FM radio stations separated by distances that are beyond the direct operating range of their FM radio sets.
  • By the commanding general, division staff, and other designated key personnel in the division when operating from a mobile CP to contact division elements connected to the division area communications system.
  • For initial establishment of telephone service from the division area communications system to using units.
  • For voice communications between mobile combat elements in the division forward area and supporting division logistic elements in the rear area.

  • For communications between low-flying Army aircraft operating in distant parts of the division area and airstrips of flight control elements connected to the division area communications system, when direct FM radio cannot be maintained.
  • For communications between forward air controllers and the air liaison officer's communications facilities when these facilities are connected with the division area communications system.
  • To keep commanders and staffs in contact with subordinate and higher headquarters, as required, during the displacement of CPs.
  • To connect two switchboards and to span a break in a wire line between units.
  • For communications during river crossings.

F-5. NRI Equipment

The equipment authorized for NRI stations is based on the unit's mission. However, equipment authorized is normally designated as NRI equipment either by paragraph number or by section. Most NRI facilities use AN/VRC-12 series radio sets. The following paragraphs discuss equipment used for NRI:

Radio Control Set AN/GSA-7.

Radio Control Set AN/GSA-7 is a small, lightweight electronic switching device used to interconnect single-channel FM radio equipment with the local, push-to-talk telephone system. The radio control set can be used in wire-to-wire (via radio), wire-to-radio, or radio-to-wire communications up to a distance of 16 kilometers (10 miles).

Radio Control Set AN/GRA-39.

Radio Control Set AN/GRA-39 is a substitute item for the AN/GSA-7. The AN/GRA-39 may be used to provide remote control of a radio receiver-transmitter up to approximately 3.2 kilometers (2 miles). This equipment may be used to provide NRI between a Telephone Switchboard SB-22/PT and the receiver-transmitters.

Additional telephone systems and radio equipment.

Manual switchboards (Figure F-1).

  • SB-22/PT.
  • SB-86/P.
  • SB-3082/GT.

Figure F-1. Manual switchboards.

Manual switchboard configurations (Figure F-2).

  • AN/MTC-1.
  • AN/MTC-3.
  • AN/MGC-9.
  • AN/TTC-35.
  • AN/TTC-23.
  • AN/TTC-29.
  • AN/MTC-7.

Automatic switch AN/TTC-38 (300- and 600-line). Figure F-2. Switchboard configurations.

Radio equipment (Figure F-3).

  • Radio Set AN/VRC-49 (2 ea RT-524/VRC receiver-transmitters).
  • Receiver-Transmitter RT-524/VRC.
  • Receiver-Transmitter RT-841/PRC-77.
  • Receiver-Transmitter RT-505/PRC-25.
  • Telephone Set TA-312/PT.
  • Installation kits.
  • Cable Assembly CX-7474 (for use with the AN/VRC-12 family).

Figure F-3. Radio equipment.

Figure F-3. Radio equipment (continued).

F-6. Security of an NRI System

NRI systems can be secured through the use of the Vinson secure equipment. (Secure wire line with KY-57s and HYX-57s.) Wire-line Adapter HYX-57 provides the interface for the KY-57 to a standard 2- or 4-wire transmission line, but it does not encrypt or decrypt. This is done by the KY-57. Distance between HYX-57s should be no greater than 16 kilometers (10 miles). If a secure wire line is required over a distance greater than 16 kilometers (10 miles), two HYX-57s can be placed back-to-back to double the range.

Security of an NRI system using the Nestor secure equipment (KY-38 and KY-8) (Figure F-4) is limited to secure radio. The wire line portion is not secure. Users of this type of NRI system must be aware of the security risk that the wire line adds. The enemy will associate call signs with unit or telephone numbers on the wire line. Long calls or trunk lines where possibility of hostile wire tapping exists must be used with caution.

The NRI station can call a radio station that has a KY-38 installed, whether the KY-38 is in the plain or cipher mode. The NRI stations cannot call a radio station with a KY-8 installed if the KY-8 is in the cipher mode. A station with either type of security equipment (KY-8 or KY-38) can call the NRI station by switching to the plain mode.

Figure F-4. KY-38.

Section III.
Operation

F-7. Responsibility for NRI Systems

The operator of the NRI system is responsible for installing, operating, and maintaining an NRI facility that will connect the radio system and the telephone system. There are times when the commander and certain key personnel of the command elements must have access to both the telephone and the tactical radio systems through the NRI facility. This provides the commander with a more flexible means of command and control. The responsibility of the NRI operator does not stop at the NRI facility. When a problem occurs, the operator should be able to locate its source. That means the NRI operator must know what happens at the switchboards, automatic switches, NRI equipment, and the radio site.

F-8. Switchboards and Switches Used With the NRI System

SB-22/PT.

The SB-22 (Figure F-5) is the simplest switchboard used with NRI. Connect a field wire pair to the binding posts on the back of the switchboard that match the line pack selected for NRI use. The other end of the pair goes to the NRI rig. The switchboard is not located in the NRI rig; it is usually the unit or area switchboard.

Figure F-5. SB-22/PT.

SB-86/P, AN/MTC-3, AN/TTC-23, and other similar units.

Use an extra switchboard cord such as the one on the SB-22, SB-86, or AN/MTC-1 type switchboard. If a switchboard cord is not available, use a PJ-051 (Figure F-6) three-conductor telephone plug and connect a piece of two-wire cable to the ring and tip of the plug. Connect the wires coming from the tip and ring of the plug to the binding posts of a TA-312 telephone. Position the telephone where the switchboard operator can reach it, and hang the plug where the operator can insert it into any jack on the board.

Figure F-6. Hookup.

SB-86/P configurations.

In a vehicle mounted configuration with more than one SB-86/P, such as the AN/MTC-3, set the TA-312 on top of one of the SB-86s. Allow the cable to hang so that the plug end can be inserted into any jack on either switchboard. Terminate the line from the NRI site on the binding posts of the TA-312. In an AN/MTC-3, for example, connect the line from the NRI site to spare binding posts A in the signal entrance box. Inside the shelter, at the binding post and jack panel, connect binding posts A to the TA-312 located on top of the switchboard.

AN/MTC-1 and AN/TCC-7 configurations.

In the AN/MTC-1, place the TA-312 on the table behind operator number 1. Run the cable overhead from the TA-312 binding posts and hang it where it can be plugged into any jack on position number 1. Terminate the line from the NRI site at the binding posts of the TA-312. In the AN/MTC-1, this can be done by connecting the line from the NRI site to the PHONE 1 MTA-4 binding posts in the power and signal entrance box of the AN/MTA-3. Inside the AN/MTA-3, connect a phone cable with a two-conductor plug to the TA-312 binding posts and insert the plug end into the PHONE 1 MTA-4 jack on the signal duct. Do not plug a phone into the PHONE 1 MTA-3 jack in the AN/MTA-4.

SB-3082/GT.

Net radio interface is possible through the SB-3082 (Figure F-7); however, it won't work on a push-to-talk basis. This means that the NRI operator must assist the call by using the push-to-talk switch on the NRI equipment handset to key the transmitter for the telephone subscriber. For NRI with the SB-3082, hook up the pair of wires from the NRI rig to one of the lines on the switchboard. Set the toggle switch on the NRI line to MAG. No special actions are required of the switchboard operator. Figure F-7. SB-3082/GT.

AN/TTC-38.

Have the AN/TTC-38 switch attendant program the NRI line as to 20-Hz, 2-wire ringdown circuit using terminal code 34. This gives the dual-tone, multi-frequency (DTMF) telephone (TA-341) subscriber direct access to the NRI 20-Hz phone without assistance from the AN/TTC-38 operator. The AN/TTC-38 operator will have to assist on all calls originating from a radio station.

F-9. Switchboard Operator Sequence of Events

SB-86/P switchboard operator sequence of events (subscriber origination).

The subscriber signals the switchboard. A drop appears on the board. The switchboard operator plugs in an answer cord and answers. The subscriber asks for the NRI operator. The switchboard operator unplugs the answer cord from the subscriber's jack. If the subscriber's telephone is set for CBS, the signal will drop again and the buzzer will sound. The switchboard operator inserts the plug of the cord connected to the NRI telephone into the subscriber's jack. This will restore the signal, if it dropped, and connect the subscriber to the NRI rig. The switchboard operator cranks the TA-312 handcrank, picks up the handset, and waits for the NRI operator to answer. When the NRI operator answers, the switchboard operator hangs up the handset and processes other calls. When the call is completed, the NRI operator rings the switchboard to tell the switchboard operator to disconnect.

AN/MTC-1 and AN/TTC-7 switchboard operator sequence of events (subscriber origination).

The subscriber signals the switchboard. A light appears on all three positions. A switchboard operator plugs in an answer cord and answers. The subscriber asks for NRI. If operator number 2 or 3 answered the call, the operator will tell operator number 1 to pick up the NRI call on the number 1 board. Operator number 2 or 3 will unplug when operator number 1 plugs in. Switchboard operator number 1 plugs the telephone cord into the subscriber's jack, picks up the TA-312 handset, cranks the TA-312, and listens for the NRI operator to answer. Operator number 1 must tell the other operators not to plug into the circuit which is being used for NRI. A busy test of the subscriber's jack on position number 2 or 3 will not indicate busy; but, if an operator plugs into the circuit, the NRI call will be interrupted. The line can be checked using the handset of the TA-312. At the end of the call, the NRI operator signals the switchboard: the TA-312 buzzer sounds. Operator number 1 picks up the handset and is told by the NRI operator to disconnect.

SB-86, AN/MTC-1, and AN/TTC-7 sequence of events (radio origination).

The NRI operator signals the switchboard. The TA-312 at the switchboard buzzes. The switchboard operator picks up the TA-312 handset and answers. The NRI operator gives the switchboard operator the desired telephone number. The switchboard operator plugs the cord connected to the TA-312 into the desired subscriber's jack, cranks the TA-312, and listens to the TA-312 handset for the subscriber to answer. The switchboard operator replaces the handset on the phone and continues to handle other calls. Operator number 1 must tell the other operators not to plug into the telephone circuit which is receiving the NRI call. The NRI operator processes the call and rings the switchboard operator when the call is completed. The TA-312 in the switchboard rings, the switchboard operator picks up the handset, and is told to unplug the TA-312 cord from the switchboard.

F-10. NRI Equipment, Configurations, Hookups, and Procedures

The following information explains the connections for, and the operation of, NRI using the AN/GSA-7 (Figure F-8) and the AN/GRA-39 (Figure F-14). Use the AN/GRA-39 only if the AN/GSA-7 is not available. These instructions apply to an NRI system using the AN/VRC-49 radio. If you have only one RT-524, the following change to these instructions will apply. For a call originating from a telephone, the NRI operator will tune the NRI radio to the frequency of the desired station and instruct the radio station to tune to the NRI frequency. The NRI operator then returns the radio to the NRI frequency to complete the call.

Figure F-8. Radio Set Control AN/GSA-7.

Figure F-9. NRI hookup using the AN/GSA-7.

Using the AN/GSA-7.

NRI hookup. The following equipment will be needed: Radio Set Control AN/GSA-7, Telephone Set TA-312, Radio Set AN/VRC-49 or Receiver-Transmitter RT-524, and Handset H-33 or equivalent. The circled numbers are keyed to Figure F-9.

Connect the two wires from the unit switchboard to the line binding posts of the AN/GSA-7. (1)

Connect the TA-312 to the same binding posts with a short pair of wires. (2) Set the switch on the TA-312 to LB.

Connect the CX-7474/W from the radio jack on the AN/GSA-7 to the RETRANSMIT R/W jack on the RT-524. (3)

Connect handset H-33 or equivalent to the PHONE jack. (4)

Set the C.O. POWER switch on the AN/GSA-7 to EXT. (5)

If using AC power, set the POWER SELECT switch to match the input voltage. (6)

Connect the AC or DC power cable (depending on the power source). Also see Figure F-10. (7)

Connect the RC-292 (or the OE-254) or the whip antenna to the ANT jacks on both transmitters with coaxial cable. (8)

When using the whip, either on the vehicle or raised up on the AB-9()3, connect the antenna control cables between the ANT CONT jacks (9) on both RT-524s and the connectors on the base of the antennas (Figure F-11). When you use an RC-292 or OE-254, you don't use the control cable.

Do not remove the X-MODE covers. (10) The set won't work with the covers removed. Figure F-10. Check polarity.

Figure F-11. Base of antenna AS-1729/VRC (whip). Connect a microphone to the C-2299. (16)

Set the POWER switches (13) on both RT-524s to LOW.

Set the SQUELCH switches (11) according to local directives.

Set the BAND switch, MC TUNE, and KC TUNE controls on RT-524 number 1 (12) to the assigned NRI frequency. Read it in the window. Don't set RT-524 number 2 on the NRI frequency.

Turn the speaker switches to ON. (14)

Set the VOLUME controls to mid range. (15)

System testing. Set the OFF-AC-DC switch on the AN/GSA-7 to AC or DC depending on the power source. Allow warm-up time. (Figure F-12.)

NOTE: If the radio keys and stays keyed, reverse the leads from the switchboard at the binding post on the AN/GSA-7.

Figure F-12. Line connections.

Turn the RADIO & MON/TEL switch to TEL-R to ring the switchboard. Release the switch. It will return to TEL-T. Use the handset of the TA-312 or the handset connected to the PHONE jack to talk to the operator. Request a ringback. The buzzer in your TA-312 should ring.

Turn the RADIO ∧ MON/TEL switch to RADIO ∧ MON-T. Check your CEOI for the frequency and call sign of a known operating station. Set the RT-524 number 1 on this frequency. Using the handset on the TA-312 or the handset connected to the PHONE jack on the AN/GSA-7, call the station for a communications check. If the station doesn't answer, set the power switch to HIGH and call again (Figure F-13). During transmission, a beep should be heard about every 5 seconds to remind the users that it is an unsecured NRI circuit.

When you finish the communications check, turn the POWER switch on the radio back to LOW, tune back to the NRI frequency, and set the switch on the AN/GSA-7 back to TEL-T.

Set the C-2299 to TRANS 2. Use the mike on the C-2299 and test RT-524 number 2.

Figure F-13. RT-524.

Figure F-14. Radio Set Control Group AN/GRA-39.

NRI call originating from a telephone subscriber.

NOTE: In the following discussion, you are presumed to be the 1-77 Infantry Battalion NRI operator. The commander of the 1-77 Infantry Battalion desires an NRI call to the commander A/1-77 Infantry Battalion. (Telephone subscriber does not have the radio call signs). Unclassified unit designators will not be linked with call signs.

When a call comes from a telephone network user, your TA-312 buzzer will buzz.

You can answer with either the TA-312 handset or the handset connected to the PHONE jack. Obtain the required information and tell the caller to stand by.

NRI OP: "SERVANT 134".

TEL SUB: "This is SERVANT 106, SERVANT 140 please."

NRI OP: "Roger--Wait--OUT."

NOTE: NRI operator determines necessary call signs and contacts requested party. In the event the requested party is not operating on your frequency, you must enter his net and request he meet you on your frequency.

NRI OP: "C46, this is A81--OVER."

RADIO SUB: "A81, this is C46--OVER."

NRI OP "This is A81, stand by for A46--OUT."

NOTE: NRI operator provides telephone subscriber with the necessary call signs and reminds him to use proper radiotelephone procedures.

NRI OP: "Sir, you are A46, your party is C46. You must use proper radiotelephone procedures. This circuit is not secure. Go ahead with your call--OUT."

Set the switch on the AN/GSA-7 to RADIO & MON-T.

Any one of three conditions will occur.

The telephone subscriber will be able to control the transmitter from his or her telephone set. This happens if the subscriber's telephone is set for local battery (LB) and is connected to the same switchboard as the NRI rig. In this condition, just monitor the call.

The second possible condition is that the transmitter will key as soon as the switch is moved to RADIO ∧ MON-T for the telephone subscriber to talk and unkeyed by setting the switch to TEL-T for him to listen.

The third possible condition is that the subscriber will be unable to key the transmitter from his or her telephone set and it does not key when the AN/GSA-7 is set to RADIO ∧ MON-T. This occurs if the AN/TTC-38, or SB-3082 switch is used, or if the call comes over a multichannel system. In this condition, leave the AN/GSA-7 switch in TEL-T. Key the transmitter with the switch on the TA-312 handset, or the handset connected to the PHONE jack, for the telephone subscriber to talk. Unkey it for the subscriber to listen.

NOTE: If you can find out beforehand what type telephone system is in your area (CB, LB, automatic switch), you should be able to tell how the transmitter is to be keyed.

Monitor the call. If feedback from the speaker causes erratic keying or squealing, turn off the speaker and monitor with the handset.

When the call is over, ring the switchboard operator and tell him or her to disconnect. Return the switch on the AN/GSA-7 to TEL-T.

NRI call originating from a radio station.

NOTE: In the following discussion, you are the brigade NRI operator. The B/1 -77 Infantry Communications Chief (radio subscriber) desires an NRI call to the 1st Brigade COMSEC Officer Unclassified unit designator will not be linked with call signs.

If necessary, the radio subscriber requests permission to leave his net.

Radio subscriber contacts the BDE NRI station on the BDE NRI frequency.

RADIO SUB: "W6T81, this is H8Q48--Request permission to enter net--OVER."

NRI OP: "H8Q48, this is W6T81--Identify your station--OVER."

RADIO SUB: "W6T81, this is H8Q48--Refer to Bravo Juliet--OVER."

NOTE: The NRI operator may elect to use abbreviated call signs once the station has been identified.

NRI OP: "Q48. this is T81--authenticate. Juliet Lima--OVER."

RADIO SUB: "T81, this is Q48--I authenticate, Whiskey--OVER."

NRI OP: "This is T81--Roger--OVER."

NOTE: In the event the requested party is not served by the NRI operator's switchboard, the full call sign and item number identifier will be given.

RADIO SUB: "This is Q84--Request contact with T36--OVER."

NRI OP: "This is T81 Roger--Wait--OUT."

NOTE: NRI operator determines switchboard designator and number and establishes contact with requested party.

SWBD OP: "SHAMROCK."

NRI OP: "SHAMROCK 167 please."

TEL SUB: "SHAMROCK 167."

NRI OP: "This is SHAMROCK 134. You have a radio call from H8Q48. Refer to Bravo Juliet. You are T36. You must use proper radiotelephone procedures. This circuit is not secure. Do you have any questions? Stand by--OUT."

NRI OP: "Q48, this is T81. Go ahead with your Call--OUT."

Switch the AN/GSA-7 to RADIO ∧ MON-T. Refer to the previous sequence for difference in transmitter keying with CB, LB, or automatic switches.

When the call is completed, return the AN/GSA-7 switch to TEL-T. Ring the switchboard to tell him to disconnect the call.

Using the AN/GRA-39.

NRI hookup. The following equipment will be needed: Radio Set Control Group AN/GRA-39, Switchboard SB-22/PT, Radio Set AN/VRC-49 or Receiver-Transmitter RT-524,18 Batteries BA-30/U, Connector U-182/U or Connector U-229/U, and 1 meter (about 3 feet) of 2-wire cable. Have your repairman build a cable as follows: Connect one wire of the 1-meter (3-foot) cable to pin A and the other wire to pin C of the U-182 or U-229 connector. Strip the insulation from about 2 centimeters (3/4-inch) of the wires on the other end. The circled numbers are keyed to Figure F-15.

NOTE: The connector is the same as the one on your RT-524 handset or mike.

Install four BA-30s in the SB-22 and six BA-30s in both the C-2328 and the C-2329.

Connect the WD-1 from the unit or area switchboard to a pair of line binding posts on your NRI SB-22. (1)

Insert the connector of the 2-wire cable to the audio jack on the C-2328. (2)

Connect one of the stripped wires of your homemade cable to the bottom binding post of the C-2328. (3)

Decide which line pack on the SB-22 is to be used for NRI. Connect the other stripped wire to one of the binding posts (4) that matches the selected line pack.

Run a wire (5) from the other binding post of the SB-22 to the top binding post of the C-2328.

Connect the C-2328 binding posts to the C-2329 binding posts. (19)

Connect the RADIO cable (6) on the C-2329 to the RETRANSMIT R/W jack on RT-524 #1.

Connect the mike to one of the audio connectors (7) on the C-2299.

Connect the coax cables from both RT-524s to both antennas. (8)

Connect both antenna control cables if you are using the vehicle whip. (9)

Set the SQUELCH on both RT-524s according to local directives. (10)

Set the RT-524 #1 BAND switch, MC TUNE, and KC TUNE controls to the NRI frequency. (11)

Turn both RT-524 speakers on. (12)

Adjust the RT-524 VOLUME controls during operation. (13)

Connect the SB-22 headset microphone to the SB-22 HEADSET connector. (14)

Set the SB-22 visual and audible alarm switch to AUD.

Turn on the C-2329. (16)

Set the C-2328 VOLUME control to mid range. (17) Make the final volume adjustment during operation.

Set both RT-524 power switches to LOW. (18)

NOTE: If the transmitter keys and stays keyed, reverse the two wires (4) and (5) connected to the NRI line pack on the back of the SB-22.

Figure F-15. NRI hookup using the AN/GRA-39.

System testing. Check your SOI for the frequency and call sign of an operating station. Set the RT-524 #1 on the frequency.

Set the C-2328 switch to RAD.

Plug the switchboard operator's cord into the line pack used for NRI.

Put the headset on, squeeze the switch in the headset cord (Figure F-16), and using radio procedure call the radio station.

Release the switch to listen. Adjust the headset audio using the VOLUME control on the RT-524.

If the station does not answer, set the RT-524 on HIGH power and try again.

After completing the radio check, put RT-524 back on LOW power, unplug the operator's cord from the NRI line pack (Figure F-17), and plug into the line pack connected to the area switchboard. Set the switch on the C-2328 to TEL. Turn the handcrank on the SB-22 to signal the area switchboard. Ask the operator to give you a ringback.

Figure F-16. Headset switch.

Figure F-17. Switchboard connections for subscriber radio link, NRI. After the switchboard communications check, plug the SB-22 operator's cord into the operator's jack on the operator's pack.

Set the RT-524 #1 back on the NRI frequency.

Set the C-2299 RAD TRANS switch to 2. Using the mike on the C-2299, make a radio check with the same station. When you finish testing, set the C-2299 back on RT 524 #1.

NRI call originating from a telephone subscriber. (Call originates from a telephone. Refer to the AN/GSA-7 sequence for typical conversation.)

The drop on the line pack connected to the area switchboard will turn to white and the buzzer will sound.

Plug the operator's cord into the area switchboard line pack jack and, using the SB-22 handset, answer the call. Lock the cord switch in the middle position.

Obtain the required information from the caller. Tell the caller to stand by.

Check the SOI for the call sign and frequency.

Give the telephone caller his or her call sign and the call sign of the person being called, if necessary.

Set the RT-524 #2 to the frequency of the station being called.

Set the C-2299 to TRANS 2. Use the mike on the C-2299 and call the radio station.

When the radio station answers, tell the radio operator to tune to the NRI frequency and to call back. Set the C-2299 to TRANS 1.

When the radio operator calls back, answer the call by using the mike on the C-2299. Tell the operator to stand by for an NRI call.

Plug the cord of the line pack connected to the area switchboard into the jack on the NRI line pack and, talking into the SB-22 headset mike, tell the telephone subscriber to go ahead. Tell the subscriber to use radio procedure and that the circuit is not secure.

Set the switch on the C-2328 to RAD. Monitor the call.

NOTE 1: If the telephone subscriber can't key the transmitter with the push-to-talk switch, key the transmitter for the subscriber by squeezing the switch on your headset cord.

NOTE 2: If the transmitter keys and stays keyed when the switch is set to RAD, the telephone subscriber probably has a common battery phone. If this happens, you can key the transmitter by setting the switch on the C-2328 to RAD when the telephone user talks and setting it to TEL when the user listens.

NOTE 3: If the sound from the speaker causes squealing or erratic keying, turn off the speaker and monitor the call through the headset.

When the call is finished, unplug the NRI line pack cord, set the C-2328 switch to TEL, ring the switchboard, and tell the operator to disconnect the line cords. Plug the SB-22 operator's cord into the jack on the operator's pack and wait for another call.

NRI call originating from a radio station. (Refer to the AN/GSA-7 sequence for typical conversation.)

The call will be heard on the RT-524 #1 speaker.

With the switch on the C-2299 at position TRANS 1, answer the call using the mike connected to the C-2299. Get the required information from the radio operator. Tell the operator to stand by.

Plug the SB-22 operator's cord into the jack on the line pack connected to the area switchboard. Turn the crank on the SB-22.

When the area switchboard operator answers, use the SB-22 headset mike. Tell the operator that you have an NRI call and give the desired number.

When the desired party answers, say that the line is not secure. Advise the party of the assigned call sign, to use radio procedures, and to stand by.

Plug the cord from the area switchboard line pack into the NRI line pack jack.

Use the mike connected to the C-2299 and tell the radio operator to go ahead with the call. Set the switch on the C-2328 to RAD. Monitor the call.

NOTE 1: If the telephone subscriber can't key the transmitter with the push-to-talk switch, key the transmitter for the subscriber by squeezing the switch on your headset cord.

NOTE 2: If the sound from the speaker causes squealing or erratic keying, turn off the speaker and monitor with the headset.

NOTE 3: If the transmitter keys and stays keyed when the switch is set to RAD, the telephone subscriber probably has a common battery phone. If this happens, you can key the transmitter by setting the switch on the C-2328 to RAD when the telephone user talks and setting it to TEL when he or she listens.

When the call is completed, unplug the NRI cord, ring the switchboard, and tell the operator to disconnect.

Plug the operator's cord into the jack on the operator's pack and wait for the next call.

Section IV.
Radio Set Control C-6709/G

F-11. Typical Usage

The C-6709/G will extend push-to-talk control of a wire-connected radio set at the NRI station to 2-wire/4-wire telephone users. This will allow the telephone user to talk and listen to a remote radio user. Control tones generated by using the keyset of the 2-wire or 4-wire telephone will control the transmitter/receiver in the transmit or receive mode. The station operator at the manned NRI station will answer and extend calls by dialing into the 4-wire automatic system and will respond to and place calls to the radio user's system. At the conclusion of a call, the normal release signal will reset the equipment for another call. The control unit will be capable of being mounted in the vehicle that houses the radio equipment. Connection between the control and Radio Set AN/VRC-12 or any other radio set will be accomplished by means of standard cables shipped with the C-6709/G. The equipment will be powered by the vehicular battery through Radio Set AN/VRC-12 or an equivalent power source. Figure F-18 shows the control unit, and Figure F-19 illustrates a typical system.

Figure F-18. Radio Set Control C-6709.

Figure F-19. Typical C-6709 system.

F-12. Equipment Characteristics

The C-6709/G is in a waterproof enclosure with a cover held by four latches. The cover has an air relief valve for equalizing air pressure before opening. All controls and interconnections are on the front panel which is accessible when the cover is removed. The cover contains a small canvas bag used to store a spare lamp and fuse. A separate canvas bag is used to store cables, headset, and two mounting brackets used to mount the C-6709/G in a vehicle. Table F-1 lists some electrical characteristics.

Table F-1. Electrical characteristics.

F-13. Mission of the System

Mode of Employment.

Radio Set Control C-6709/G will be used to provide integration facilities between 2- or 4-wire telephones and a push-to-talk radio system. A subscriber is connected to 4-wire central offices, and push-to-talk AN/VRC-12 type radio sets. Other type push-to-talk radios can be used with this device if connecting cables are compatible.

Purpose.

Radio Set Control C-6709/G is part of a reliable, high quality, automatic, electronic, 4-wire switching system. It is a lightweight, completely solid state, single-channel, attended radio set control device. The control provides a means for the telephone subscriber with a push-button telephone to control transmission and reception of a remote radio used in an NRI system.

System Applications.

The C-6709/G may be used with several radio sets, COMSEC devices, and telephone switching equipment (Table F-2).

Table F-2. Equipment compatible with the C-6709.

F-14. Location

This equipment is designed to be mounted in a vehicle along with the radio set with which it is being used. Space requirements are illustrated in Figure F-20. When the C-6709/G is used with some radio sets (such as the AN/VRC-12), it uses the radio set power supply. In some cases, an external 24 volts DC power supply is needed. The C-6709/G is normally mounted so the operator has easy access to the radio set. The use of an external 24 volts DC power supply will be required when using any radio/crypto sets other than the AN/VRC-12. The connection for these radio/crypto sets will be made to a pair of binding posts on the front panel of the C-6709/G. The wire/cable and the connectors (for example, alligator clips for 24 volts DC vehicle battery) are not supplied as a component with the equipment when used with the list of radio/crypto sets other than the AN/VRC-12.

Figure F-20. Vehicle space requirements for C-6709.

F-15. Operation

Call originating from a radio station.

NOTE: In the following discussion you are the 1-77 Infantry Battalion NRI operator. The Commander, 1-77 Infantry Battalion desires an NRI call to the Commander A/1-77 Infantry Battalion. (Telephone subscriber does not have the Radio call signs.) Unclassified unit designators will not be linked with call signs.

You receive a call from a radio station. You will hear the call in your H-250 handset or H-325 headset microphone. You may hear the call over the radio speaker, if the radio set is so equipped.

RADIO SUB: "A81, this is A46--OVER."

If the C-6709/G has been placed in the proper standby condition, you need only to key the transmitter to answer the call. If you are using the H-250 handset, key the radio by depressing the push-to-talk (PTT) switch and unkey it by releasing the PTT switch. If you are using the H-325/TTC headset microphone, you key the radio by depressing key number 1 on the C-6709/G keysender and unkey by depressing key number 3. If the C-6709/G is not in the proper standby condition, you must place the C-6709/G MODE switch to the OPER position; this permits you to key your radio on and off. You next depress the C-6709/G OPER CONNECT RADIO pushbutton; this connects the C-6709/G to the NRI transmitter-receiver. You may now key your radio on and off as outlined above.

NRI OP "This is A81--OVER."

NOTE: In the event the requested party is not served by the NRI operator s switchboard, the full call sign and item number identifier will be given.

RADIO SUB: "This is A46. Request contact with C46--OVER."

NRI OP: "This is A81--Roger--Wait--OUT."

You consult the SOI and telephone directory to determine the telephone number for the desired party.

You depress the C-6709/G OPER CONNECT SWBD pushbutton; this connects the C-6709/G to the automatic switchboard. The C-6709/G SVC REQ/BUSY lamp will come on and remain lit and you will receive a dial tone from the switchboard. You then key the number of the desired party on the keysender of the C-6709/G.

NOTE: If you misdial the number, depress the C-6709/G RLSE pushbutton; this disconnects the C-6709/G from the switchboard and places it in a standby condition. The C6709/G SVC REQ/BUSY lamp will go out. Again depress the C-6709/G OPER CONNECT SWBD pushbutton and proceed as above.

When the telephone is answered, get the desired party on the line and tell him or her there is an incoming NRI call. Because a telephone user doesn't usually have an SOI, you will have to give the subscriber the call sign to use. You and the subscriber now must determine the type of radio transmitter keying control the subscriber will use. If the subscriber is using a telephone handset that has a push-to-talk (PTT) switch, the SF (PTT) position of the C-6709/G MODE switch may be used. In this position the transmitter is keyed when the PTT switch is depressed and held, and is unkeyed when the PTT switch is released. If the subscriber has a telephone with a keysender, the DTMF 1/3 position of the C-6709/G MODE switch may be used. In this position, the transmitter is keyed when the subscriber presses key number 1 on the keysender and is unkeyed when key number 3 is pressed. The subscriber may choose, as an alternative, to use the AVOX position of the C-6709/G MODE switch. In this position, the transmitter is keyed when the subscriber is speaking and is unkeyed when he or she is silent. You must remember the type of transmitter control used. The switchboard subscriber is then told to stand by for the NRI call.

TEL SUB: "SERVANT 140."

NRI OP: "This is SERVANT 134. You have a call from A46. What type of telephone equipment are you using?"

TEL SUB: "TA-312."

NRI OP: "Your call is from A46. You are C46. You must use proper radiotelephone procedure. This circuit is not secure. Stand by--OUT."

You depress the C-6709/G OPER CONNECT RADIO pushbutton; this transfers the connection of the NRI operator from the switchboard subscriber to the radio transmitter.

NOTE: The C-6709/G SVC REQ/BUSY lamp will remain lit, indicating that the C-6709/G is still connected to the switchboard subscriber. Using the H-250 handset or H-325/TTC headset microphone, establish contact with the radio station. Tell the radio subscriber to then go ahead with the call.

NRI OP: "A46, this is A81. Go ahead with your call--OUT."

You set the C-6709/G MODE switch to the AVOX position.

NOTE: At this time the C-6709/G MODE switch will be set to one of the three positions, as determined by you and the switchboard subscriber.

You then depress the C-6709/G CALL CONNECT OPER IN pushbutton. This disconnects you from the switchboard subscriber, and connects the switchboard subscriber and the radio station to a common talk path within the C-6709/G. When the C-6709/G CALL CONNECT OPER IN pushbutton is depressed, you can monitor both sides of the NRI talk path. You cannot transmit to either party.

Monitor the NRI talk path to ensure that the switchboard subscriber can key the transmitter on and off and that good communications between the two parties has been established. If for some reason the switchboard subscriber cannot key the transmitter, you must set the C-6709/G MODE switch to the OPER position and key the transmitter on and off at the appropriate times for the switchboard subscriber. After a good NRI connection has been made, you must monitor to ensure proper radio procedure is being used.

NOTE: As long as the NRI call is in progress, the C-6709/G SVC REQ/BUSY lamp will remain lit.

When the NRI call has been completed and the switchboard subscriber hangs up the handset, the C-6709/G SVC REQ/BUSY lamp will go out, and the C-6709/G is automatically placed in a standby condition. When this occurs, you should place the C-6709/G MODE switch to the OPER position and depress the OPER CONNECT RADIO pushbutton. You are now ready to answer the next service request. If it is by radio, you need only key the transmitter to answer. If the request is by telephone, you need only to depress the C-6709/G OPER CONNECT SWBD pushbutton to answer. If the C-6709/G SVC REQ/BUSY lamp does not go out within a reasonable time, you should depress the C-6709/G CALL CONNECT OPER IN pushbutton. This will enable you to monitor the NRI talk path. If the call has been completed, you should then depress the C-6709/G RLSE pushbutton. This will disconnect the C-6709/G from the switchboard and place the C-6709/G into a standby position. You should then place the C-6709/G MODE switch to the OPER position and depress the OPER CONNECT RADIO pushbutton. You are then ready for the next service request, as outlined above.

Call originating from switchboard subscriber.

You receive a call from a switchboard subscriber. This is indicated on the C-6709/G by the audible alarm and flashing SVC REQ/BUSY lamp.

Depress the C-6709/G OPER CONNECT SWBD pushbutton. This connects you to the switchboard subscriber. The audible alarm will go off and the SVC REQ/BUSY lamp stops flashing and remains lit.

Answer the call by using the H-325/TTC headset microphone or H-250 handset. Obtain from the subscriber the individual or station the caller desires. Because a telephone user does not usually have a CEOI, you will have to look up the call signs and frequency and give the call sign to the subscriber. You and the subscriber will have to determine the type of radio transmitter keying control the subscriber will use. If the subscriber is using a telephone that has a push-to-talk switch, the SF (PTT) position of the C-6709/G MODE switch may be used. In this position the transmitter is keyed when the PTT switch is depressed and held, and is unkeyed when the PTT switch is released. If the subscriber has a telephone with a keysender, the DTMF 1/3 position of the C-6709/G MODE switch may be used. In this position, the transmitter is keyed when the subscriber depresses key number 1 on the keysender and is unkeyed when the subscriber depresses key number 3. Alternately, the subscriber may choose to use the AVOX position of the C-6709/G MODE switch. In this position the transmitter is keyed when the subscriber speaks and is unkeyed when he or she is silent. Remember the type of transmitter control used. Tell the switchboard subscriber to standby while the desired party is contacted by radio.

NRI OP: "SERVANT 134."

TEL SUB: "This is SERVANT 106, connect me with SERVANT 140."

NRI OP: "What type of telephone equipment are you using?"

TEL SUB: "TA-838."

NRI OP: "Roger--Wait--OUT."

Depress the C-6709/G OPER CONNECT RADIO pushbutton. This transfers you from the switchboard subscriber to the NRI radio receiver-transmitter. Note that the C-6709/G SVC REQ/BUSY lamp will remain lit, indicating that the C-6709/G is still connected to the switchboard subscriber. Set the radio to the frequency of the desired party. Place the C-6709/G MODE switch in the OPER position. You may now key the radio on and off. If you are using handset H-250, key the radio by pressing the PTT switch and unkey the radio by releasing the PTT switch. If you are using headset microphone H-325/TTC, the transmitter is keyed when you depress key number 1 on the C-6709/G keysender and is unkeyed when you depress key number 3.

NRI operator determines necessary call signs and contacts requested party. In the event the requested party is not operating on your frequency, you must enter his net and request he meet you on your frequency.

NRI OP: "C46, this is A81--OVER."

RADIO SUB: "This is C46--OVER."

NRI OP: "This is A81--Stand by for a call from A46--OUT."

Depress the C-6709/G OPER CONNECT SWBD pushbutton. This disconnects you from the receiver-transmitter and makes connection to the switchboard subscriber. Provide the telephone subscriber with the necessary call signs and remind him to use proper radiotelephone procedure.

NRI OP: "Sir, you are A46. Your party is C46. You must use proper radiotelephone procedure. This circuit is not secure. Go ahead with your call--OUT."

Set the C-6709/G MODE switch to the AVOX position.

NOTE: At this time the C-6709/G MODE switch will be set to one of the three positions, as determined by you and the switchboard subscriber earlier.

Depress the C-6709/G CALL CONNECT OPER IN pushbutton. This disconnects you from the switchboard subscriber, and connects the switchboard subscriber and radio station to a common talk path within the C-6709/G. When the C-6709/G CALL CONNECT OPER IN pushbutton is depressed, you can monitor both sides of the NRI talk path. You cannot transmit to either party.

Monitor the NRI talk path to ensure that the switchboard subscriber can key the transmitter on and off and that good communications between the two parties has been established. If for some reason the switchboard subscriber cannot key the transmitter, you must set the C-6709/G MODE switch to the OPER position and key the transmitter on and off at the appropriate times for the switchboard subscriber. After a good NRI connection has been made, you must monitor to ensure proper radio procedure is being used.

NOTE: As long as the NRI call is in progress, the C-6709/G SVC REQ/BUSY lamp will remain lit.

When the NRI call has been completed and the switchboard subscriber hangs up the handset, the C-6709/G SVC REQ/BUSY lamp will go out. The C-6709/G is automatically placed in a standby condition. When this occurs, place the C-6709/G MODE switch to the OPER position and depress the OPER CONNECT RADIO pushbutton. You are now ready to answer the next service request. If it is by radio, you need only to key the transmitter to answer. If the request is by telephone, you need only to depress the C-6709/G OPER CONNECT SWBD pushbutton to answer.

If the C-6709/G SVC REQ/BUSY lamp does not go out within a reasonable time, depress the C-6709/G CALL CONNECT OPER IN pushbutton. This will enable you to monitor the NRI talk path. If the call has been completed, depress the C-6709/G RLSE pushbutton. This will disconnect the C-6709/G from the switchboard and place the C-6709/G into a standby condition. Place the C-6709/G MODE switch to the OPER position and depress the OPER CONNECT RADIO pushbutton. You are now ready for the next service request as outlined above.



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