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Nowadays cellular operators in Indonesia are allocated frequency band for UMTS systems in 2.1 GHz band as well as two channels with each channel allocated at 5 MHz. Bandwidth to meet the 3G service was ranging started from 1920 MHz to 1980 MHz for uplink and 2110 MHz it up to 2170 MHz for the downlink it. The number of channels in both uplink and downlink bandwidth is twelve with each frequency channel has a width band of 5 MHz. Currently the remaining unallocated channel is channel 11 and 12. Along with the traffic growth and RPJP, the allocation of the two channels surely increase the capacity and the throughput of 3G operators. The allocation of these two channels are been realized at least on the first quarter of 2012; with the auction system by BRTI. However, the results of field tests conducted by several operators and BRTI, show that if both channels are allocated to operators for 3G services, the transmitter from CDMA2000 base station which is allocated its downlink frequency at 1983.125 MHz to 1990 MHz will interfere with the receiver base station of 3G GSM, operators which will be allocated in blocks 11 and 12. If interference occurs, the quality of service of 3G GSM operators will significantly decrease. Of course this is a consideration of the relevant institutions and 3G operators who wish to be allocated to one or two channel. This interference can be overcome by manual calculation from link budget and antenna spacing between CDMA2000 antenna Tx to UMTS antenna Rx that operate on blocks 11 and 12. This calculation is based from antenna characteristics equation with assumptions and interference constraints defined by 3GPP and 3GPP2. This solution is specifically performed between CDMA2000's base station and UMTS base station which are located at Hotel Pangrango 2 (Bogor), Infil Limo (Depok), and Cengkareng (Tangerang).