Chapter 7
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7-1.5 Meters for M/W System 1. Power Meter Anritsu - ML 4803 A 2. Power Meter HP - 437 B, 4368, Philips 3350 3. Spectrum Analyzer- Anritsu MS 7101 B,10 KHz- 23 GHz, 22 GHz- 140 GHz. 4. M/W System Analyzer (MSA) Transmitter & Receiver ME 538 M Anritsu 4510 B Transmitter and Receiver. 5. M/W frequency counter Anritsu MF 76 A 6. Sweep Generator programmable Marconi instrument 10Mhz-20 GHz 7.
7-1.6 Before proceeding any M/W system A/T --------1] Get TT-O, TT-1 duly filled in all respect, 2] Collect Survey report which includes, - Check list - Route details - Site survey report - Particulars at a glance - Clearance calculation - Path data calculation - Rain attenuation calculation - Availability calculation - Interference calculation - Tower diagram - Line diagram - Path profile - Site map Here you have to check the deviation in survey and nominal level which should not be more than ±3 dBm. N.B.
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7-2 MICROWAVE SYSTEM A/T Microwave A/T comprises of - Local A/T of all stations, and Repeaters. - Hop Test. - Through Test. 7-2.1 Local A/T:There are several makes of Narrow / Wide band microwave systems, near about all test are same except power supply points, access points. Here for example Satara M/W station to T.E. end link of 11 GHz (1+ 1) digital M/W system MakeHFCL, is described. 1. Check of power supply:Measure voltage at Battery point and Bay input, note down the voltage drop. Limit :- 1.0 V.
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3. Test on receiver:- Check of RLO frequency :- Check of RLO frequency with unritsu or HP frequency counter, measure frequency and offset Write assigned measured and deviation in PPM limit ±20 PPM Measure RLO output level at RLO mon limit ≥-12 dBm Feed Receive RF frequency at a level of -30 dBm at RX, RF and record 1.RF frequency limit ±250Khz 2. If level at AGC out (IF out) limit -5 ±1 dBm 3.
7-2.2 VSWR: - Voltage standing wave ratio Standing wave :- If the impedance of the load (Antenna) and source ( Generator ) is not equal, that is not matching then part of the energy is reflected back towards the source., some power is absorbed and rest is reflected .this interference form one set of waves V & I traveling towards the load and reflected set travels back to generator. These two sets of traveling wave moving in opposite direction 180 out of phase.
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MSA Transmitter -10 IF in 201 IF O/P 70 75 Ω termination MSA Receiver Counter IIF return loss IF in on Rx card Fig. 7-10 Conversion chart of VSWR, Return Loss and SWR. VSWR 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.18 1.20 1.30 1.50 1.43 1.38 1.33 1.29 1.25 1.222 1.196 1.173 1.152 1.135 1.119 1.106 1.094 Return loss In dB 46.1 40.1 36.6 34.2 32.3 30.7 29.4 28.3 27.3 26.4 25.7 24.9 24.3 23.7 23.1 21.7 20.8 17.7 14.0 15.0 16.0 17.0 18.0 19.0 20.0 21.0 22.0 23.0 24.
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Please see the Wiltron diagram, Anritsu detector converts power into voltages. - Connect Open , select - Connect Short , select - Connect device , - Start select, - Function, - Max /select -20 dBm, - Min / select -34 dBm, - Cursor also move for max to minimum. Wiltron Generator: - See Fig. 7-12, 7-13. - Take 10.7 to 11.
4. Check of BER with IF Loop: Loop IF Trans to If Receive and test 140 Mb/ STM-1 on DTA set for 0 PPM and ± 15 PPM. The result should be 0.00 E-11 5. a) Trans Branching Filter loss: The difference between Trans Power at PA out and antenna port will be a Trans Branching Filter loss. b) Receive Filter loss: Feed RF Frequency at a nominal level to antenna port and measure at Rx in, Calculate receive filter loss. Limit: - Tx + Rx combined filter loss should be 6 dB max. 6.
7-2.4 HOP A/T OF 11 GHz 140 Mbps or STM-1 1] Receive level: - Note down Surveyed level, Nominal level and measure Rx RF level at Rx IN by power meter with suitable sensor and pad by removing the W/G from RF IN. - The same Rx RF level can be measured with calibrated spectrum analyzer and by tuning the required frequency of a channel, deviation between measured and surveyed should be within ±1 dBm. - The deviation between surveyed and nominal level should be within ±3 dBm.
4] BER measurement:- Ask distant station loop on 140 Mb or STM-1 which is installed. - Carry out BER Test as usual for 0 and ± 15/20 PPM. - Take out printout for each channel/PPM , - Limit: - 1x 10 E -11 5] Jitter measurement :- ( as mentioned in OFC systems Pl) Carry out I/P Jitter test for both Main and Protection channels for the following frequencies: - 200 Hz, 500 Hz, 10 KHz, 3500 KHz, and note down the results in UIPP. O/P Jitter: - Select Filters as HP-1+LP & HP-2 +LP. For Limits pl see the table.
7-3 Microwave constituents 7-3.1 1. Antenna: - It is a metallic device which transmits and receives Radio signals in the form of electromagnetic waves. Antenna used for the transmission of Radio, TV, M/W, GSM and CDMA network. There are two types of antennas. 1. Omni directional (radiates equally in all direction) It is a simple rod. 2. Directional (radiates in one direction only) - Yagi : - Directional antenna of array of dipoles.
7-3.2 3. Link Budget:Link budget is to calculate particular M/W system Receive level taking into consideration all gains and losses in the network. It accounts attenuation of transmitted signal due to propagation. Formula: - Pt + Gt + Gr – L – FL – Br Where Pt – A Transmitter power. Gt + Gr - Antenna gain in both directions. L - Free space loss. FL – Feeder cable loss in both directions. Br – Branching filter loss at both end.
7-3.3 5. Fresnel zone: No. of concentric ellipsoid revolutions which defines volumes in radiation pattern of circular aperture and it is due to diffraction by circular aperture The first zone is circular; sub second zones are annular in cross section and concentric with first. This zone concept is used to analyze interference by obstacle near the path of radio beam. TR – Direct path and TAR – Secondary transmission path by reflection of M/W energy from A. T A R Hilly Terrain 6.
7-3.4 8. Rain attenuation: - As the water droplets scatters and absorbs radiation the effect of rain goes on increasing with the increase of frequencies i.e. it is more in 13 GHz system compared to 4 and 6 GHz Formula A (dB) = 0.0308 f – 0.1872R, R - Rain rate at that location = -----------Where f = operating frequency within 10-15 GHz This rain attenuation can be reduced by interconnecting two stations separated by distance greater than likely size of rain cell i.e. by space diversity.
Antenna diversity: - In this diversity scheme microwave signals are transmitted along with different propagation path with the help of second antenna at receiving end to improve received performance. 7-3.5 10. Hot stand by: If main equipment fails automatic switch over takes place on a stand by equipment set i.e. a complete set of parallel equipment is switched in almost instantaneously on failure of operating equipment. This is also called a equipment diversity.
13. Wayside dropping: - If any small station in any hop requires 2 MB stream, an additional card is provided in system so as to handle the traffic of small station along with main M/W system. 14. IF DADE: - Differential Absolute Delay Equalizer. It is to adjust the phase difference between signals received through main and space diversity antenna. This phase difference causes loss of bits. DADE cable is used and it is placed between IF out and RX2 IN.
7-4 2 GHz / 8 MB D/ UHF System A/T Make: - ARM-2208-M3 7-4.1 Specification: - Frequency band 2.0 to 2.3 GHz. - Bit Rate 8.448 MHz 75 Ω. - Tx- Rx Spacing 161 MHz. - RF Tx: +30 to +32 dBm at antenna port. - Receive IF frequency 70 MHz. - Transmitter PA out +34 dBm max. - AGC dynamic range 45 dBm for threshold. - Ref Rec. I/P level -42 dBm ± 1 dBm. - Overload of LNA -35 dBm or better. - Receive Threshold for BER of 1 x 10-3 -86 dBm at Rx In. - O/W response ± 2 dBm. - Noise level -53 dBm. 7-4.
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- Disconnect RF cable from Rx In. Make a test set up as above for AGC calibration. Select RF frequency and level say -40 dBm and calibrate it for the correct O/P level. Put ON RF O/P and monitor AGC voltage. Note down AGC voltage up to -75 dBm in steps of -10 dBm and there after in 5 dBm steps when E-3 LED lights. Reading will be -86 to -89 dBm. Limit is -86 dBm at Rx IN.
7-4.4 HOP/ through A/T 1. Receive level: - Measure RF Rx level at Rx IN and compare it with surveyed level. - Deviation between surveyed and measured level should be within ±1 dBm. (Ref: - DOT ML sector 7 GHz/ 34 Mb) 2. BER test: - Ask distant station to loop all four tributaries and check BER on all four Trbs for 0 and ± 50 PPM for 5 minutes each. Limit: - 0.00 E-10, No Error. 3. Check of switching operation: - Take loop on one tributary from distant station.
6. - Tele command status TC1, TC2 OFF. BITE Alarms: Eqpt fail: - Any Eqpt failure. System fail: - Any System failure. Microprocessor fail: - When processor in supervisory card out. OB call tone busy: - When Bus call is sent EOW: - When O/W call is in progress. 7. - Alarms: - Monitor following various alarm on Transmitter. Data fail T/R unit when I/P HDB3 data failure. RF fails in BITE. When power <+30 dBm.
