v20161108
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  1. Using a ProFlex 800 as a
    Continuously Operating Reference Station (CORS)

    (Mark Silver, ms@igage.com, +1-801-412-0011)

    The ProFlex 800 is a great solution for a CORS station, static campaign or a community base.

    Here are my notes on provisioning a ProFlex 800 CORS station:

    1. Read the NGS CORS Bible: [ CORS Guidelines (pdf) - Feb 2006 ]; Read the [ UNAVCO CORS Monumentation PDF ], [ CORS Guidelines ]; These [ guidlines ] from New South Wales are excellent.

    2. Consider your site location carefully:

    Site Selection: The perfect site is going to be difficult to find. Every site you consider will have some feature which sucks. My concerns, in order of importance are:

    1. Permanence. We don't want to go through all the trouble to setup a CORS site and then have the building remodeled a year later and force a relocation. Stay away from roof mounts because when the roof is replaced, the CORS site will have to be taken offline. A great CORS location will be a great location for communication antennas also, try to pick a location that won't have a tower erected nearby after CORS is commissioned.

    2. Stability. (See http://www.ngs.noaa.gov/PUBS_LIB/GeodeticBMs ) Masonry buildings (over 5 years old) or piers may be best, but if you set a new structure it is going to take a long time to settle into a permanent location unless you are are really careful. Consider future buildings, future trees (will you be allowed to cut down every tree within 50 meters for the next 100 years?). Remember that you want 1 mm stability. That is a tough row to hoe.

    A masonry building with cracked walls is unacceptable.

    3. Obstructions. None above 10 degrees, best if none above 5. No obstructions above 0 degrees within 3-meters.

    4. Interference. Power-lines, cell towers, UHF and VHF towers (if you are going to broadcast corrections, try to put your UHF antenna directly north of the GNSS antenna. Try to choose a location without any metal roof flashing nearby. Any metal roofs in the vicinity is bad.

    5. Security. The site needs to be secure against copper thiefs, equipment theft and meddlers. Don't place the antenna in location where it will be backed into by trucks, or accidently nicked by heavy equipment.

    3. Mount. Use the SECO mounts built for this purpose: http://www.surveying.com/products/details.asp?prodID=2072-Series No reason to reinvent the wheel. These are great solutions and are available with 1.5", 2" and 3" pipe thread on the bottom. Seco recommends #2072-50 leveling vial for leveling the mount, I prefer the #2002-00 Tribrach Adjuster.

    4. Building attachments. There are lots of methods, I think the best way to choose one is to look at some of the recently NGS accepted attachments:

    5. Cable.I recommend that you have less than 75 meters (250 feet) of feedline. No Matter What. So you need to site the receiver within 220 feet of the GNSS antenna.

    You can purchase prebuilt cables, but the ends will be pretty big and require giant holes in the building or large conduit. I prefer to run the cable, cut to length and terminate the ends where I need them. It makes for a neater installation. I have seen many installations with 10 meter cable runs that have 20 meters of coiled cable next to the receiver. More is not better when considering cable length.

    I prefer to encase the cable in metallic conduit. If that is not possible, secure the cable using bushing clamps every four feet.

    The cable length will determine the minimum cable specifications. Here is how to compute the allowable cable loss...  NGS specifies 9 db of loss total from antenna to receiver, Considering lightning protection and connection loss:

    Diamond Antenna SP3000W Lightning Protector  - 0.3 db
    2 N-Connectors (on Lightning Protection) -0.15 db @  - 0.3 db
    2 TNC-Connections (on antenna and receiver) -0.15 db @  - 0.3 db
    Total loss other than cable  - 0.9 db

    This leaves 8.1 db of loss for the cable, from which we can derive these maximum cable lengths (at 1.3 GHz):

    Cable Type Loss / 100' at 1.2 GHz Maximum Length
    Times LMR 400 4.75 db /100' 170 feet (52 M)
    Times LMR 240 9.16 db / 100' 88 feet (27 M)
    RG-8 8.25 db / 100' 98 feet (30 M)
    Times LMR-200 12.00 db / 100' 67 feet (20 M)
    RG-58 17.65 db / 100' 45 feet (14 M)

    6. Lightning Protection:

    SP3000W Lightning Surge Protector

    Always include a lightning protection device. If your GNSS antenna takes a direct hit, the antenna, the cable, the receivers will all be pool of metal (the plastic will have vaporized). But if there is just a static event (like a nearby strike), then Lightning Protection will/may/might save your receiver!

    I recommend the Diamond Antenna SP3000W (DC to 3GHz, 200W) for both the GNSS and UHF radio. You will also need to provide a low-impedance path to ground.

    7. Internet Connection: You will need a reliable internet connection. You will need to be able to forward an outside static IP address through the router using port 80 (HTTP Web Interface), port 22 (FTP) and any ports you export Direct IP data from. FTP will also require "Stateful Packet Inspection" to support passive FTP transfers.

    Most IT departments are going to be freaked out when you ask them to allow FTP access inside a router. If the IT department is small, it may not be a problem. If the IT department is big, this may be the single most difficult issue concerning deployment. (Many dozen donuts may be required to soften up the IT department. :)

    7. GNSS Equipment: The ProFlex 800 L1/L2 without GLONASS is the most cost effective high performance receiver. If you choose a GNSS antenna (like the Ash661) then you can add GLONASS at a later date with no cost penalty.

    A 16 GB thumbdrive will hold about 2.5 years of archived GNSS (GPS+GLONASS) 5-second data. I prefer to completely configure the receiver via a command file named 'autoconfig.cmd' on the root of the USB attached thumbdrive. Using this strategy, I can replace the receiver or upgrade firmware, when the receiver boots, I press the button to run the command file and the new receiver is completely configured.

    Here is a real command file for the CORS station on my chimney:

    $PASHS,ETH,ON Turn on Ethernet port power
    $PASHS,ETH,PAR,DHP,0,ADD,10.1.16.7,MSK,255.255.255.192,
       GTW,10.1.16.62,DN1,8.8.8.8,DN2,192.168.1.26
    Configure ethernet port, mask, gateway and DNS servers
    $PASHS,TCP,PAR,MOD,1,LGN,igage,PWD,xxxx,PRT,8888 Turn on TCP/IP server with authentication
    $PASHS,WEB,PAR,ON,AdminName,AdminPassword,80 Turn on Web Server, set Admin name and password
    $PASHS,WEB,OWN,Mark's Chimney CORS,Mark Silver,ms@igagecom,+1-801-412-0011 Set owner's name (on the web server splash screen)
    $PASHS,WEB,USR,ADD,NGS_NOAA,noaapassword Setup a dedicated user account for NGS
    $PASHS,WEB,USR,ADD,user,pswd Setup a dedicated user account for general users
    $PASHS,EFT,PAR,LGN,admin,PWD,bry1,MEM,2,PTH,bry1,PRT,21 Setup the internal FTP server, admin name and password, serve files from the "/bry1/" path on the USB thumbdrive
    $PASHS,EFT,USR,ADD,NGS_NOAA,noaapassword Setup a read only password for NGS
    $PASHS,EFT,USR,ADD,user,pswd Setup a read only password for general users
    $PASHS,EFT,ON Turn on the FTP server
    $PASHS,SVM,25 Set the max number of tracked SV's to 25
    $PASHS,STI,23 Set the broadcast station ID to 23 (sent to rovers)
    $PASHS,DYN,1 Set the receiver dynamics to 'Static'
    $PASHS,PEM,5 Elevation mask for position processing
    $PASHS,ELM,0 Elevation mask for raw data, data recording, differential data (must be 0 for NGS CORS)
    $PASHS,ANR,ARP Antenna Reduction Mode = ARP, ANT and ANH are ignored. The base position is the ARP.
    $PASHS,ANT,0,0,0 Ignored, but Antenna Offset
    $PASHS,ANP,OWN,ASH111661,12345,0 Antenna type and serial number
    $PASHS,ANP,OUT,OFF Disable Virtual Antenna
    $PASHS,POS,4206.7913503,N,11234.217050,W,1234.589 Set the position of the base, ddmm.mmmmmm format, height in meters
    $PASHS,GLO,ON Enable GLONASS (if option is present)
    $PASHS,SBA,ON Enable SBAS (WAAS)
    $PASHS,PRT,B,7 Set port B to 38,400 baud (connects to ADL radio)
    $PASHS,BAS,B,CMP Set port B to CMR+ differential message
    $PASHS,CPD,MOD,BAS,2,0 Set receiver to Base, GPS+GLO, Static Base
    $PASHS,BDS,CMP,I1,ON Set differential stream types for all 9 ports
    ...  
    $PASHS,BDS,ATM,I9,ON 9th port
    $PASHS,DST,I1,ON,1,0,7201 Enable Stream 1 on port 7201, server mode
    ...  
    $PASHS,DST,I9,ON,1,0,1002 Stream 9
    $PASHS,RNX,TYP,4,1,16 RINEX type 4 (L1&L2 SNR, position every 12 Epochs), once per second, attributes every 16 second.
    $PASHS,SES,OFF Turn off data recording sessions
    $PASHS,SES,AUT,000000,24,0100,5 Set for 24 sessions, based at the top of every hour
    $PASHS,SES,PAR,DAY,1,OFS,0,SIT,sgu1,MEM,0,RNX,1,CMP,1,DEL,0,
       MOV,2,DST,2,PTH,s/Y/D/s,FTP,0,RFM,Y
    Store sessions in internal memory, convert to rinex, compress, move to USB in folder "site/yyyy/ddd/site", don't push ftp to remote site, com
    $PASHS,RXC,PAR,AGY,Mark Silvers Chimney,OBN,IGAGEMC,MNM,BRY1,
       MNB,BRY1,OBS,BRY1 ANT_ASH111661 SN_12345
    Information for RINEX conversion
    $PASHS,SES,ON Turn on Sessions

    8. GNSS Antenna:

      vs.

    The Ash661 antenna is a great antenna for under $2,000. The 111584 is a great choke ring antenna for under $5,000. The 111584 is a slightly better antenna than the ASH661 (fewer very low angle slips). From a performance standpoint it is very, very difficult to measure any difference.

    The choice is yours :)

    9. UHF Radio for Real-Time Corrections: The ProFlex 800 supports up to two external radios (no option purchase is required.) For UHF operation, choose the Pacific Crest ADL Vantage Pro radio.

    Purchase these components:

    87400-00-S ADL Vantage Pro Radio
    ADL 35W Radio 430-470 MHz
    A00630  Ashtech Serial Data Cable
    A82024  DL Vantage Pro Desktop Power Supply  
    C02086 450-470 MHx Unity Gain Fixed Installation Antenna
    84269 ADLP wall mount with fan  
      Antenna Cable, Lightning Protector as needed
    (TNC on radio, N on Lightning Protection and N-Female on Omni)
     

      

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