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== Antenna calculations ==
 
Every HP-node has two 5.15-5.6 GHz antennas. The one as a build in patch antenna and the other is an 5.1-5.8 GHz omni-directional antenna. The idea is that the patch antenna of a node will either be aligned to the omni or the patch antenna of another node. The following calculations is to get an feeling of what distances should be possible between these antennas.
 
South African Wifi channels:
Channel  1 : 2412  Mhz 11g          Channel  48 : 5240  Mhz 11a
Channel  2 : 2417  Mhz 11g          Channel  52 : 5260* Mhz 11a
Channel  3 : 2422  Mhz 11g          Channel  56 : 5280* Mhz 11a
Channel  4 : 2427  Mhz 11g          Channel  60 : 5300* Mhz 11a
Channel  5 : 2432  Mhz 11g          Channel  64 : 5320* Mhz 11a
Channel  6 : 2437  Mhz 11g          Channel 100 : 5500* Mhz 11a
Channel  7 : 2442  Mhz 11g          Channel 104 : 5520* Mhz 11a
Channel  8 : 2447  Mhz 11g          Channel 108 : 5540* Mhz 11a
Channel  9 : 2452  Mhz 11g          Channel 112 : 5560* Mhz 11a
Channel  10 : 2457  Mhz 11g          Channel 116 : 5580* Mhz 11a
Channel  11 : 2462  Mhz 11g          Channel 120 : 5600* Mhz 11a
Channel  12 : 2467  Mhz 11g          Channel 124 : 5620* Mhz 11a
Channel  13 : 2472  Mhz 11g          Channel 128 : 5640* Mhz 11a
Channel  36 : 5180  Mhz 11a          Channel 132 : 5660* Mhz 11a
Channel  40 : 5200  Mhz 11a          Channel 136 : 5680* Mhz 11a
Channel  44 : 5220  Mhz 11a          Channel 140 : 5700* Mhz 11a
 
HP-Node detailed specs: http://wirelessafrica.meraka.org.za/wiki/images/0/07/WLAN-A0033.pdf
 
Pigtail detail specs: http://wirelessafrica.meraka.org.za/wiki/images/0/0a/Ca178_cable_assemblies_datasheet.pdf
 
Wireless adapter detail specs: http://wirelessafrica.meraka.org.za/wiki/images/2/21/Wlm54sag23.pdf
 
OR the Mikrotik version of the same adapter called a R52H (also manufactured by Compex, but usually cheaper)
http://wirelessafrica.meraka.org.za/wiki/index.php/Image:R52H.pdf
 
Another popular adapter is the DCMA-82 from Wistron. They have better RX sensitivity, but lower output power and they are a bit more expensive than the Compex cards. In some of the discussions that I've seen they state that the DCMA-82 has much cleaner output power, better RX sensitivity, and a lower failure rate/quality issues than Compex's cards.
http://wirelessafrica.meraka.org.za/wiki/index.php/Image:DCMA-82.pdf
 
Node specs summary:
Patch antenna            - 21-23 dBi,  16 deg H,  11 deg V, 5.15 -5.6 GHz
5Ghz Omni antenna        - 8-11 dBi,    360 deg H, 10 deg V, 5.1 - 5.85 GHz
2.4Ghz Omni antenna      - 7.5-8.5 dBi, 360 deg H, 12 deg V, 2.4 - 2.5 GHz
30mm U.FL-SMA pigtail    - RG178 cable insertion loss, 2.4 GHZ = -1.1dB, 5.6 GHz = -2dB
Compex WLM54AG23 adapter - IEEE 802.11a/b/g (2.4/5GHz)
                          - AR5413/5414(AR5006X/XS) Atheros Chipset
                          - RECEIVER SENSITIVITY 802.11a -
                            -90 dBm @ 6Mbps
                            -70 dBm @ 54Mbps
                          - OUTPUT POWER 802.11a
                            23dBm @ 6-24Mbps
                            22dBm @ 36Mbps
                            19dBm @ 48Mbps
                            17dBm @ 54Mbps
Mikrotik (Compex) R52H  - IEEE 802.11a/b/g (2.4/5GHz)
                          - AR5413/5414(AR5006X/XS) Atheros Chipset
                          - RECEIVER SENSITIVITY 802.11a -
                            -90 dBm @ 6Mbps
                            -70 dBm @ 54Mbps
                          - OUTPUT POWER 802.11a
                            24dBm @ 6-24Mbps
                            22dBm @ 36Mbps
                            19dBm @ 48Mbps
Wistron DCMA-82          - IEEE 802.11a/b/g (2.4/5GHz)
                          - AR5413/5414(AR5006X/XS) Atheros Chipset
                          - RECEIVER SENSITIVITY 802.11a -
                            -90 dBm @ 6Mbps
                            -82 dBm @ 36Mbps
                            -72 dBm @ 54Mbps
                          - OUTPUT POWER 802.11a
                            22.5dBm @ 6-24Mbps
                            21.5dBm @ 36Mbps
                            18dBm @ 48Mbps
 
I could not find any receive sensitivity info for ranges between 6Mbps and 54Mbps for the WLM54AG23. The closest I could find was the specs of another manufacturer card, using the same Atheros chipset as the WLM54AG23. Here is the receive sensitivity info for a WMIA-166AG Dual-Band miniPCI module (802.11a/g)
Nominal Temp Range:
  6Mbps 10-5 BER @ -90 dBm, typical
  9Mbps 10-5 BER @ -89 dBm, typical
12Mbps 10-5 BER @ -88 dBm, typical
18Mbps 10-5 BER @ -86 dBm, typical
24Mbps 10-5 BER @ -82 dBm, typical
36Mbps 10-5 BER @ -78 dBm, typical
48Mbps 10-5 BER @ -72 dBm, typical
54Mbps 10-5 BER @ -68 dBm, typical
 
The WLM54AG23 is not the best wifi adapter in the market, but it gives a good compromise between price vs performance. If one need to push the limits of a specific link then I would probable select the SR5 from Ubiquity. They have excellent TX power and RX sensitivity.
There are lots of wifi/antenna/distance calculators available on the WEB. Most of these calculators cannot calculate the max distance for a link, you have to specify the distance and it will calculate you dBm margin. Links to a couple of Wifi/antenna/distance calculators:
 
http://www.radiolabs.com/stations/wifi_calc.html
http://www.zytrax.com/tech/wireless/calc.htm
http://www.widgetbox.com/widget/wifi-link-calculator
http://www.wifiextreme.com.au/index.php?main_page=page_5
http://www.rflinx.com/help/calculations
http://www.olotwireless.net/castella/radio.htm
 
Here are some formulas use to calculate a link budget:
  Free space loss = 36.56 + 20Log10(Frequency) + 20Log10(Dist in miles)
  mW to dBm = 10Log10(milliWatts) + 30
  dBm to mW = 10(dBm/10)
  RX Power = Margin - RX sensitivity
  Theoretical margin = TX power budget + RX power budget - free space loss
  SAD factor = Theoretical margin/TX power budget * 100 and shows the percentage of spare power on transmission.
 
(Free Space Loss) = 92.5 + (20 Log fequency) + (20 log km distance)
 
Free space loss @ 5400GHz:
1km = -107.07dB      11km = -128.028dB
2km = -113.09dB      12km = -128.784dB
3km = -116.61dB      13km = -129.479dB
4km = -119.11dB      14km = -130.123dB
5km = -121.05dB      15km = -130.722dB
6km = -122.63dB      16km = -131.282dB
7km = -123.97dB      17km = -131.809dB
8km = -125.13dB      18km = -132.305dB
9km = -126.15dB      19km = -132.775dB
10km = -127.07dB    20km = -133.221dB
 
The following are the minimum and maximum link calculations for our HPNode with a 5Ghz patch to omni link under ideal conditions with a decent fresnel zone. Just note that one very seldom get ideal conditions in real life installations. These calculations are done to get a feeling for what to expect from our equipment. Link distance calculations was done with these calculator at http://www.swisswireless.org/wlan_calc_en.html. I've first played around with the Free-space-loss values in the Link Budget tool until I would get a 6dB margin. They recommend to take a sufficient security margin (5-6 dB or more on large distances). Then I've used the Free space loss tool to convert my Free-space-loss value to a km distance. Lets do some calculations to see what we get.
 
Patch - Omni:
Min link distance @ 54Mbps 0.9km:              Max link distance @ 54Mbps 1.55km:
patch min        = 21dBi                      patch max      = 23dBm
omni min        = 8dBi                        omni max        = 11dBm
pigtail          = -2dBm                      pigtail        = -2dBm
TX power        = 17dBm                      TX power        = 17dBm
RX sensitivity  = -70dBm                      RX sensitivity  = -70dBm
Free space loss  = -106dB                      Free space loss = -111dB
link margin      = 6dB                        link margin    = 6dB
 
Min link distance @ 24Mbps 6.9km:              Max link distance @ 24Mbps 12.3km:
patch min        = 21dBi                      patch max      = 23dBm
omni min        = 8dBi                        omni max        = 11dBm
pigtail          = -2dBm                      pigtail        = -2dBm
TX power        = 23dBm                      TX power        = 23dBm
RX sensitivity  = -82dBm                      RX sensitivity  = -82dBm
34km free space  = -124dB                      Free space loss = -129dB
link margin      = 6dB                        link margin    = 6dB
 
Min link distance @ 6Mbps 17km:                Max link distance @ 6Mbps 30.9km:
patch min        = 21dBi                      patch max      = 23dBm
omni min        = 8dBi                        omni max        = 11dBm
pigtail          = -2dBm                      pigtail        = -2dBm
TX power        = 23dBm                      TX power        = 23dBm
RX sensitivity  = -90dBm                      RX sensitivity  = -90dBm
34km free space  = -132dB                      Free space loss = -137dB
link margin      = 6dB                        link margin    = 6dB
 
The following are the minimum and maximum link calculations for our HPnodes with a 5Ghz patch to patch link under ideal conditions with a decent fresnel zone. Just note that one very seldom get ideal conditions in real life installations. These calculations are done to get a feeling for what to expect from our equipment. Link distance calculations was done with these calculator at http://www.swisswireless.org/wlan_calc_en.html. I've first played around with the Free-space-loss values in the Link Budget tool until I would get a 6dB margin. They recommend to take a sufficient security margin (5-6 dB or more on large distances). Then I've used the Free space loss tool to convert my Free-space-loss value to a km distance. Lets do some calculations to see what we get.
 
Patch - Patch:
Min link distance @ 54Mbps 3.9km:              Max link distance @ 54Mbps 6km:
patch min        = 21dBi                      patch max      = 23dBm
pigtail          = -2dBm                      pigtail        = -2dBm
TX power        = 17dBm                      TX power        = 17dBm
RX sensitivity  = -70dBm                      RX sensitivity  = -70dBm
Free space loss  = -119dB                      Free space loss = -123dB
link margin      = 6dB                        link margin    = 6dB
 
Min link distance @ 24Mbps 30.9km:            Max link distance @ 24Mbps 38.9km:
patch min        = 21dBi                      patch max      = 23dBm
pigtail          = -2dBm                      pigtail        = -2dBm
TX power        = 23dBm                      TX power        = 23dBm
RX sensitivity  = -82dBm                      RX sensitivity  = -82dBm
Free space loss  = -137dB                      Free space loss = -139dB
link margin      = 6dB                        link margin    = 6dB
 
Min link distance @ 6Mbps 77.6km:              Max link distance @ 6Mbps 123km:
patch min        = 21dBi                      patch max      = 23dBm
pigtail          = -2dBm                      pigtail        = -2dBm
TX power        = 23dBm                      TX power        = 23dBm
RX sensitivity  = -90dBm                      RX sensitivity  = -90dBm
Free space loss  = -145dB                      Free space loss = -149dB
link margin      = 6dB                        link margin    = 6dB

Latest revision as of 16:27, 17 June 2009

migrated to wireless dev