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 ```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 ``` ``````## Link budget for LV2 ### What's our situation? Here are our requirements for signal strength at the receiver front end, and what the current systems provide. AM ATV (if we were to use it)
We want -53 dBm
We need at a minumum -63
We have -62
We just pass
FM ATV
We want -63 dBm
We need at a minumum -73
We have -62
We win
[[WiFi]]
We want -73 dBm
We need at a minumum -94
We have -70
We win
---- ### What signal levels are needed for ATV? - P5 signal from the ATV circuit Using FM ATV, P5 occurs at > 50 uV (-73 dBm) Using AM ATV, P5 occurs at > 150 uV (-63 dBm) At 5 uV (-93 dBm), AM and FM are at the same level of "snowyness." It is best to exceed the needed signal requirement by 10 dB to allow sufficient fade margin. **For FM ATV, we need -63 dBm to give P5 picture with 10 dB of fade margin.** For AM ATV would need -53 dBm for P5 and 10 dB fade margin. ### What signal levels are needed for [[WiFi]]? - A SINAD that allows 11 Mbps on the [[WiFi]] circuit This SINAD can be obtained with -83 dBm at the [[WiFi]] card. A SINAD allowing the lower limit of 1Mbps on the [[WiFi]] circuit is acheivable with -94 dBm signal at the [[WiFi]] card. It is best to exceed the needed signal requirement by 10 dB to allow sufficient fade margin. **For [[WiFi]] we need -73 dBm at the receiver to give 11 Mbps and the desired fade margin.** ### Whats available? - Antenna and amplifier gains - Path losses The **path loss due to free space** can be found using an equation from [Andrew](http://www.andrew.com) ® Catalog #33; p8; _Lfs (dB) = 96.9 + 20log10 D + 20log10 f_
D is in miles; f is in GHz; Also the path loss can be calculated using an equation found in the [ARRL](http://www.arrl.org) Antenna Book; P17-6; _Lfs = 20 Log10 4(pi)d / lambda(free space)_
where d and lambda are in the same units The freespace loss equation from the Andrew catalog will be used for this calculation. The worst case path is the distance of our spacecraft at apogee, which is 10 miles or 52,800 feet. At the ATV frequency, 1.277 GHz. Lfs = 96.6 + 20log10(10) + 20log10(1.277) = **118\.72 dB (loss)** At 2.422 GHz Lfs = 96.6 20log10(10) + 20 log10(2.422) = **124\.28 dB (loss)** ---- ### The budget Add up all the gains and losses from rocket to the ground... ATV - [[CommLinkBudgetLV2ATV21Jan2004]] - [[CommLinkBudgetLV2ATV26Jan2004]] - New [[CommLinkBudgetLV2ATV30Jan2004]] [[WiFi]] - [[CommLinkBudgetLV2WiFi21Jan2004]] - [[CommLinkBudgetLV2WiFi26Jan2004]] - New [[CommLinkBudgetLV2WiFi30Jan2004]] ---- ### Other stuff - The FM ATV exciter puts out 50 mW (+17 dBm) this needs to be attenuated by 7dB for it to match the required +10 dBm signal input of the M67715 power amplifier. This is done with a Pi attenuator added to the input of the power amplifier board. The R values are 130/47/130 ohms. - Also see System Operating Margin [(SOM)](http://www.ydi.com/calculation/index.php) described by ® Young Design, Inc.. Their calculator is very useful. Actually the calculators have been moved to the Terabeam Wireless site: [Calculators](http://www.terabeam.com/support/calculations/index.php) - The P number system is a metric for picture quality. P5 is best "closed circuit quality", and P1 is barely descernable. See ARRL Handbook. Tom O'Hara W6ORG provided the signal strength information needed for various P levels. - The units of dBm at the transmitter is the only place where reference to milliwatts is applied. All other dB values are unitless ratios, thereby the final result is in dBm. - _dBd = +2.15 dBi_