Chapter 11: Radio Communication (Analog/Digital VHF) PDF

CHAPTER XI RADIO COMMUNICATION (Analog/Digital VHF) 11.1 RADIO COMMUNICATION 11.1.1 “Communication by Radio” means the transfer of intelligence from one point to another through space using radiated electromagnetic energy (Radio...

CHAPTER XI RADIO COMMUNICATION (Analog/Digital VHF) 11.1 RADIO COMMUNICATION 11.1.1 “Communication by Radio” means the transfer of intelligence from one point to another through space using radiated electromagnetic energy (Radio Waves) (in the FREQ spectrum of from about 10KHz to about 30,000 KHz.) Radio Frequency Spectrum Class Freq. Range Wave length VLF 10-30 kHz 30,000-10,000 m LF 30-300 kHz 10,000 - 1,000 m MF 300-3000 kHz 1,000-100m HF 3-30 MHz 100-10m VHF 30-300 MHz 10-1m UHF 300-3000MHz 100-10cm MW 3 to 30 GHZ 10-1 cm 11.1.2 The objective of any communication is to pass information from one place to another. Radio Communication consists of generation, propagation and reception of electromagnetic waves. Modes used in Indian Railways are- - VHF Communication - UHF Communication - M/W Communication 11.1.3 VERY HIGH FREQUENCY (VHF) COMMUNICATION The frequency band of VHF Communication is 30 MHz to 300 MHz. The frequency allotted by WPC (Wireless Planning and Coordination wing of ministry of communication) in VHF for Indian Railways are in the band 146.2 MHz to 167.95 MHz. Communication in this range of frequencies is mainly due to line of sight, reflection and scattering of waves. 11.1.4 Uses of VHF VHF Communication is used (now a days) for many applications such as:- - Traffic Control - Police Duties - Mobile Communication - Point to Point Communication - Point to MultiPoint (Group) Communication - Disaster Management Possible uses of VHF Communication on IR are Indian Railways Telecom Manual - 2021 Page 108  - Communication during Maintenance and Construction Blocks - Yard communication - Communication in the train between Guard & Driver. - Mobile Communication in between moving train/vehicle with fixed location (Station) or another moving train/ vehicle. - Emergency Communication: o ART equipped with hand held and base station VHF sets - Duplex VHF Sets are utilised for o Extension of exchange number to distant place. o Control working.( Train Traffic Control )/Patching. 11.2 SPECIFICATION & PERFORMANCE PARAMETERS 11.2.1 VHF PARAMETERS 1. Frequency Range - 30 MHz to 300 MHz - Frequency Band used in Railways is 146.2 MHz to 167.95 MHz. - One spot frequency is used for each channel 2. Mode of Propagation: -Line of sight waves -Reflection & scattering of waves 3. Type of operation: Simplex Duplex 4. Channel capacity: - 1/16/128/256 channel - Voice or Low speed Data or both. 5. Type of Equipment: i) Walkie-Talkie (Hand Held) Set- 1W/2W to 5W switchable output power operated on in-built NiMH / Li-ion batteries. (For communication in the train in between Guard & Driver, in between moving train/vehicle with fixed location (Station) or another moving train/ vehicle, 5W sets are to be used) ii) Portable 25W VHF Sets – Portable 25W VHF Sets are normally used in Loco and vehicles operated on 12V battery set. iii) Fixed 25W VHF sets (Base Stations) – Installed at desired locations , mainly at ASM rooms. - Operating on AC Mains or by 12V battery. - External antenna with feeder cable connector mounted on a mast by itself or on Roof top as needed. ( For digital 25W Indian Railways Telecom Manual - 2021 Page 109  VHFset : RDSO specification no. RDSO/SPN/TC/107/2018 or latest , for analog 25W VHF set with secured station to station communication : RDSO Specification no. RDSO/SPN/TC/73/2008 or latest ) 6. Antennas used - Whip Antenna - Ground Plane (GP) Antenna - Dipole - Low Profile - Yagi Antenna 7. Feeder cable: - 50 Ohms Unbalanced Coaxial cable. 8. Expected Communication Range in open area: - Walkie -Talkie to Walkie - Talkie - 1 to 2 Km. - Portable Set can transmit - 12 Km to 15 Km. - Fixed 25W VHF Set to Fixed 25W VHF Set - upto 25 Kms when antenna used are directional & fixed at the height of 15 to 20 metres. The range may get reduced due to the number of parameters like terrain, ghat section, tunnels and obstructions etc. 9. License: - Mandatory As per the latest guidelines WPC license is required to be taken for each VHF set. 10. Frequencies allotment: Following frequencies has been decided by the Railway Board for different use: Indian Railways Telecom Manual - 2021 Page 110 Indian Railways Telecom Manual - 2021 Page 111 11.2.2 LIMITATIONS OF VHF COMMUNICATION - Range limited up to 25 Km maximum due to requirement of line of sight. - Dark Zones occur due to terrain, high rise buildings & other structures. - VHF sets consume more power, hence the set may require more than one battery set for long duration usage. - Interference due to other users operating at the same frequency. - Effect of prevailing noise in the surrounding. 11.2.3 Digital radio VHF sets Digital Mobile Radio (DMR) is an open standard which is not proprietary to any single manufacturer. The DMR standard specifies that DMR equipment must be compatible, so a radio will work on any base station or network, which improves availability of options and pricing. These are having several advantages in terms of Voice Quality, Coverage, Battery Life, Channel Capacity and Data Capabilities etc. In view of these additional features/advantages, Digital Walkie-Talkie sets should be preferred over Analog sets and Analog sets to be phased out gradually. Use of Licence exempted Digital VHF set allowed by WPC may be considered for maintenance purpose (non- crew usage). 11.3 INSTALLATION OF VHF - For point-to-point communication availability of line of sight is essential. - Antenna height must be decided at both locations by measuring minimum field strength needed for satisfactory communication. This can be measured by putting one trans-receiver at one end and mounting antenna at a suitable height of 15m to 20 m and measuring the field strength by field strength meter at receiving locations. VHF sets of the same power and frequency can also be installed to check the quality of communication. Antenna height and orientation can be adjusted to get a maximum signal strength or voice. - Antenna can be mounted on a tower/Mast of approved design or on a pipe on the roof of a building. Feeder cable must be of 50 Ohm. impedance unbalanced of approved design. Antenna and its feeder cable must be earthed as per earthing arrangement defined in chapter XXIII. - Connectors used must also be of good quality and supplied by an approved supplier. - 230V AC mains operated power supply of rated voltage & current is supplied by the supplier along with VHF set. A 12V/80-120 AH battery must be connected on float to the set to prevent communication failure during mains failure. 11.4 VHF Walkie/Talkie Sets 11.4.1 VHF Walkie/Talkie sets are used in several departments of the Railways. PCSTE with approval of GM and Sr. DSTE with approval of DRM shall distribute these sets among various departments and units under their jurisdiction in view of safety, train operation, security and maintenance. Indian Railways Telecom Manual - 2021 Page 112  Distribution of these sets using a pool system through crew lobby etc. should be followed to optimize the requirements of sets. 11.4.2 Procurement of VHF sets and their condemnation shall be done by the S&T department.as per RDSO procedures and Railway Board guidelines. 11.4.3 The S&T department of the divisions shall be responsible for obtaining frequency authorization and obtaining license from Wireless Planning Commission. It shall also be responsible for payment of spectrum charges and license renewal of the entire population of the VHF sets being used in the division. Funds for the procurement, initial license fee and its subsequent annual renewals of license shall be provided by the respective user department. 11.4.4 Maintenance of VHF sets a. Maintenance of the VHF sets for the entire population of the division is the responsibility of the S&T department. b. Nodal supervisors of the user department shall inform or handover defective sets to the concerned SSE/Tele. c. SSE/Tele concerned shall then arrange for repair/replacement of these sets for minor defects departmentally and for major defects through authorized agencies/OEM. d. The unserviceable handsets should be expeditiously condemned and payment of license fee for those sets to be stopped. e. VHF set’s transmitting power at different frequencies/channels are to be measured once in a year. f. Spurious emission squelch operation current drain frequency stability, frequency deviation, sensitivity of receiver & adjacent channel selectivity are to be checked once in a year in the centralized repair center or during repair through authorized agencies/OEM. g. List of Standard Testing Tools for VHF sets in the centralized repair center include Digital Multimeter, Communication radio test set, Dummy Load, Variable power supply, 0-30V, 0-30 A, Battery analyzer, Digital load for battery test, Channel programming kit etc. 11.5 INSPECTION Fixed VHF installation must be inspected every month by JE, by SSE once in six months and by ADSTE/DSTE once in a year. 11.6 FAILURE REPORT Indian Railways Telecom Manual - 2021 Page 113  - VHF system’s failure must be reported to the controlling officer daily in the morning. - Monthly statements of a failure must be reported in the PCDO to Headquarter. - Spare sets must be kept at site or at a suitable location to replace the faulty sets. -x-x-x- Indian Railways Telecom Manual - 2021 Page 114