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Published bySaul Goodrick Modified over 2 years ago

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Collocation Interference 1 WRAP 0859G

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Collocation Interference WRAP calculates all potentially dangerous frequencies due to: –Intermodulation –IF breakthrough –Image frequency –Harmonics –Transmitter spectrum –Receiver selectivity –Antenna illumination –Receiver blocking Level calculations are included 2 WRAP 0859G

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Collocation Interference WRAP calculates a set of interference free frequencies based on the settings. 3 WRAP 0859G

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Collocation Interference Calculations are performed in three levels –Probability –Frequency –Interference level 4 WRAP 0859G

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Probability Distance and EIRP criteria to select possible interfering stations. Collocation interference is only shown if the duty cycle of the possible interfering station is greater than or equal to the receiver maximum blocking. If several transmitters (N) are involved the combined probability for transmission is calculated as: 5 WRAP 0859G

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Isolation between stations Interfering signal level –I= P Tx – L b + G Rx – L cable – L add – L spectrum Antenna diagrams included except –at distances < one wavelength –collinear antenna mounting (dipoles located above each other). Stations with multiple antennas –Interference is power-summed over all TX/RX antenna pairs –Minimum value of antenna isolation is presented in the user interface 6 WRAP 0859G

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Isolation 7 WRAP 0859G

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Filtering The transmitter spectrum is defined as the power spectrum density levels* relative to the maximum level, at user defined frequency offsets from the tuned frequency. The maximum of the power spectrum density level shall be set to 0 dB. * Defined in the Occupied Bandwidth of the transmitter The receiver selectivity and external filter characteristics are defined as the attenuation at user defined frequencies. For external filters the frequencies can be defined either as absolute or as relative to the tuned frequency. 8 WRAP 0859G

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Filtering Spectrum and selectivity The calculation takes the spectrum and selectivity into account by integrating the received power over all defined frequencies. External filters are also considered. 9 WRAP 0859G

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Calculation Settings Several settings to filter and adapt input data for large-site calculations. 10 WRAP 0859G

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Interference margin The margin is calculated as –the difference between (receiver sensitivity minus required signal- to-interference ratio) and the calculated interference level –Exception for interference type “Receiver blocking”: The margin is the difference between the defined receiver blocking level and the interference level. 11 WRAP 0859G

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Co/Adjacent channel Always calculated (Checkbox: Level calculations ignored). For stations with several frequencies only the transmitter-receiver frequency pair with the smallest frequency separation is analysed. Indicated as co-channel or adjacent channel interference depending on the following expression: Level calculations are performed if the condition is fulfilled without division by 2. 12 WRAP 0859G

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Antenna illumination Calculates if there is a possible antenna illumination from any of the selected transmitters. Since no terrain database is used there may be false indications when an obstacle hides the transmitter from the receiver in the real world. The frequencies are not important since this is only a geometrical calculation. Illumination is only calculated for stations separated greater than or equal to 100 m. Not an important calculation – this is a reminiscence from an early implementation when complete level calculations were not included. 13 WRAP 0859G

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Receiver blocking Always calculated if the transmitter frequency is within the -40 dB limits of the external receiver filters. (Checkbox: Level calculation ignored.) If filters are not available the domain in the settings is used. Interference level is defined after external receiver filters but before selectivity. 14 WRAP 0859G

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Harmonics Harmonic interference of order n is present if: Level calculations are performed if the condition is fulfilled without division by 2 The transmitter harmonic attenuation is included in the interference calculation. The basic transmission loss is calculated for each harmonic. 15 WRAP 0859G

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Image frequency Image frequency coincidence is present if: Level calculations are performed if the condition is fulfilled without division by 2. The test for image frequency interference is not performed for receivers with varying IF frequency. If the LO oscillator can be both above and below the tuned frequency of the receiver both cases are considered 16 WRAP 0859G

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Image frequency The receiver image frequency attenuation is included in the interference calculation. The filtering in the receiver selectivity is performed with the selectivity curve reversed 17 WRAP 0859G

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IF breakthrough IF breakthrough is present if : Level calculations are performed if the condition is fulfilled without division by 2. IF breakthrough is not tested if the IF frequency of the receiver is varying. The receiver IF frequency attenuation is included in the interference calculation. If the local oscillator is above the tuned frequency, the selectivity curve is reversed. 18 WRAP 0859G

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Intermodulation Transmitter and receiver intermodulation 2 nd and odd orders of intermodulation Involved frequencies are within the -40 dB limits of the external filters. If filters are not available the domain in the settings is used. 19 WRAP 0859G Tx filters Tx 1 Tx filters Tx 2 Rx filters Rx f(Rx) = 2f(Tx1)-f(Tx2)

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Intermodulation Transmitters with TX Frequency = RX Frequency in a station do not contribute to intermodulation interference in their own receivers. This is internally defined as a simplex case, i. e. the transmitter can not transmit at the same time that the receiver receives. The spectrum of the intermodulation signal is set to the widest spectrum of the involved transmitters broadened by the spectrum widening factor W. The power density is adjusted by a factor 1/W. Hence, the total power of the signal is held constant. 20 WRAP 0859G

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Interference-free frequencies Automatic generation of a user-specified number of interference free frequencies IM and harmonics are considered for allotments Result can be saved as a new allotment or exported to a frequency list 21 WRAP 0859G

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Interference-free frequencies Prioritised frequencies are not included in the result, they are prioritised for other use. Stations are set to prioritised by default. The term interference-free means that the frequencies in the list shall not interfere with (or be interfered by) each other or with the frequencies set to prioritised. 22 WRAP 0859G

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Summary Time probability, frequency and level analysis of –Intermodulation –IF breakthrough –Image frequency –Harmonics –Receiver blocking –Antenna illumination –Co/Adjacent channel interference –EMI analysis with general emitters. Generation of interference-free frequencies 23 WRAP 0859G

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Summary Useful for fixed frequency, frequency hopping and direct sequence spreading (see separate presentation) Level calculations with spectrum and filtering by integration. Results at RF signal level. 24 WRAP 0859G

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