FAQs - Pre-Installation and Site Preperation

What test equipment can I use for site surveys and field strength measurements?

A spectrum analyzer that has a minimum noise floor of at least -90 dBm and a maximum frequency of 3 GHz is recommended. These are made by Anritsu , Agilent/HP, Berkeley Varitronics, Avcom/Ramsey, Root, Willtek, Rohde & Schwarz. Spectrum Analyzers may be rented by the month from many vendors such as Tucker and ElectroRent. Avcom/Ramsey makes one specifically for 2.4-2.5 GHz that sells for approx. $3000. They also offer frequency extenders for low-frequency spectrum analyzers. The Grasshopper, Cricket and Locust handheld analyzers are made by Berkeley Varitronics. Morrow Technolgies make a spectrum analyzer that can be remotely controlled over a LAN or wireless modem, model VC3500. AeroComm has introduced the new SA3000 Spectrum Analyzer for the 2.4 GHz ISM band. Site Survey tools are available on the AeroNet wireless broadband site. If you have Teletronics radios, here is a neat site-survey tool. A new handheld spectrum analyzer, Model FSH3, has been introduced by Rohde & Schwarz. Also the new 4 GHz handheld by Willtek is new.

How do I calculate my network link budget?

You should perform a network link analysis for every PtP link, and for a sampling of your PtMP links. The analysis should be calculated for both signal directions. There are many online calculators for link analysis. Some of these are Telex Link Budget Calculator, Wireless Network Link Analysis from Green Bay Professional Packet Radio, Wicklewood & Wymondham Calculators, and ElectroComm calculators. NOTE: Some WLAN radio manufacturers use the EIRP output power instead of true "radio output power" in their advertisements! Make sure that you obtain the TRUE or CONDUCTED radio output power from the FCC Test Report to use in these calculations.

What RF cable should I use for my antenna installation?

We recommend Times Microwave LMR-series , Andrew Heliax , Belden RF-series or NK Cables USA cable for the lowest losses. Times LMR-1200 or Andrew LDF5-50A Heliax will produce 2.3 dB loss in a 100 foot run. Times LMR-400 and Belden RF400 will produce 3.3 dB loss in a 15m (50') run at 2450 MHz. Belden RG-213/U cable may also be used for runs of less than 7.5m (25'). Total attenuation should not exceed approximately 3 dB. Cables and connectors may be ordered through TESSCO. Low-cost pigtail cable assemblies are available from ALLCOM, RF Cables and Cable X-perts. Check out the neat Technical Articles on the Times Microwave site. LAN Administrators and ISP's should check with the manufacturer of the WLAN system hardware before adding new cables and connectors!

What towers should I use for my Access Point antennas?

Trylon "Titan" tower models T200-72 and T200-96 are very popular and inexpensive. The new Rohn SCL towers are also available in heights from 40' to 100'. Rohn SSV series are recommended for heights of 100-150 feet. Check out AN Wireless towers also. As towers may fall under local zoning ordinances, you may also wish to consider water towers, grain elevators or utility poles as other options. Placing AP antennas higher than 100 feet exposes them to greater amounts of interference, more feedline losses, zoning restrictions, FAA lighting requirements, and larger cell areas. Existing towers may be located using these sites - TelecomSiteSource, FCC Antenna Structure Registration and Wireless Radio Tower Locator. Grain elevators may be located using this site - Grain Elevator Locator.

Can I mount an omni antenna on the side of a tower?

Ideally, an omni antenna should be placed on the tip of a mast above a tower. This will give a nice circular radiation pattern. If your tower is 300 feet high and you wish to place the omni at the 100 foot level, you will have to attach the omni to a stand-off bracket at some distance away from the tower leg. With a spacing of 6" or even 12", you will have many lobes and nulls created by the reflections from the tower. Also with close spacing, there is a greater chance that these reflections will produce an upwards or downwards beam tilt. The depth of these nulls can be reduced by a greater spacing, such as 5 feet. Make sure that your tower can handle the extra wind load of these stand-off brackets, and that the omni antenna is parallel to the tower legs at all times.

How do I perform a PtP site survey?

Initially, create a path profile using one of the various mapping programs. If LOS and Fresnel zone clearance seems good, check for trees and other unusual obstacles to LOS. A good way to check this is to place a person at each end of the path with a high-powered flashlight or large mirror and a cell-phone. While talking with each other, flash the light so that the other person can see it. UHF hand-held radios (FRS or commercial frequencies) also work well to determine LOS. Use 1 watt radios for up to 4 miles and 5 watt radios for up to 15 miles. If results look promising, place an AP at one end and a CPE at the other and try connecting using 19-24 dBi grid or panel antennas. (Do not swing both directional antennas at the same time!) Look for interference at each end by using a spectrum analyzer and both vertical and horizontal polarized antennas. If you have Teletronics radios, here is a neat site-survey tool. There are also professional consultants (e.g. Cyber-Doctors) that can perform wireless site surveys for a fee. Site Survey tools are available on the AeroNet wireless broadband site.

What connectors does Telex use?

Telex can supply antennas with almost any connector, or even without a connector for OEM applications. Standard connectors are Type N plug, Type N Jack, TNC plug, RP-TNC plug, RP-TNC jack, SMA plug, SMA jack, RP-SMA plug, MC-Card plug, and MMCX plug right angle. Cable size dictates which connectors may be used on certain antennas. LAN Administrators and ISP's should check with the manufacturer of the WLAN system hardware before adding new cables and connectors!

What do you recommend for weatherproofing connectors?

We recommend 3M vinyl electrical tape for most applications. Apply one layer of high-quality 3M (88+) tape, then one layer of mastic, then a final layer of 3M tape. (Hint: Apply the first layer of tape with the sticky surface out) Do not use any spray-on or brush-on weather-proofing material, as this is VERY difficult to remove. Times Microwave supplies both vinyl mastic weatherproofing kits as well as 3M cold-shrink weatherproofing kits. See the LMR hardware accessories at the Times Microwave LMR-series web site. Andrew also supplies cold-shrink weatherproofing kits and WeatherShield snap-on connector housings for their Heliax cables. See page 472, 499 and 509 of their catalog at the Andrew Heliax web site.

What do you recommend for antenna grounding & lightning protection?

This depends upon the type of installation. For tower-mounted antennas, there should be a good ground wire (#2/0) attached between the tower base and a single-point earth ground. (There is no need for a separate ground wire running along the tower!) For roof-mounts, the mast should be grounded to the steel structure of the building if possible. If no connection to the building is possible, then a large diameter wire may be run directly to earth ground. Lightning arrestors should be added to the coax cable between the antenna and the amplifier or other radio equipment unless built-in to the amplifier or radio. Otherwise, they should normally be installed where the coax enters a building. For more information, see technical documents at PolyPhaser. Here is a sample lightning arrestor from Alpha-Delta. Arrestors may be ordered through ALLCOM or TESSCO. Data lines running from the antenna must also be protected from lightning surges. We recommend the Tripplite and APC ProtectNet line of surge suppressors. These should be installed where the line enters the house, in a weather-protected area. If you use PoE, then choose a suppressor model rated for T1 service with a voltage-clamp at 75 volts or higher.

How can I check the VSWR of my antenna before and after installation?

The VSWR (Voltage Standing Wave Ratio) of a 2.4 GHz antenna may be checked with most HP/Agilent or Anritsu RF Network Analyzers that have a maximum frequency of 3 GHz. Lower-cost hand-held units are also available from Anritsu , Bird Electronics, and Praxsym. The Anritsu S332B Sitemaster / Spectrum Analyzer combo has both VSWR and Spectrum Analyzer features in one unit. It is also possible to use an IFR spectrum analyzer for return loss (VSWR) measurements. The WLANexpert also has VSWR measurement capabilities for PRISM chipset-based cards. Antennas at this frequency may be checked with an attached transmission line no longer than: 25 feet (LMR-400 & 600), or 5 feet (LMR-195 & RG-58). Longer cables will make the VSWR appear much lower than it really is. When testing an antenna before installation, make sure that the antenna is outdoors and pointing away from the ground and any metallic objects. A VSWR of less than 1.5:1 is excellent, and less than 2:1 is acceptable. Most antenna manufacturers spec their antennas for either 1.5:1 or 2:1 across the bandwidth.

Should I use 2.4 GHz or 5.8 GHz for my WLAN or WISP system?

Currently, most systems use either IEEE 802.11 or 802.11b operating between 2.4 and 2.4835 GHz. As these frequencies become more congested, the U-NII Band 3 at 5.725 - 5.825 GHz (IEEE 802.11a) will be used more. 5.8 GHz also offers data transmission rates greater than 11 MB/s. However, more antenna gain will be necessary at 5.8 GHz for the same distance on 2.4 GHz. 5.8 GHz will have a smaller Fresnel zone, so there may be certain advantages when shooting a signal through a tight space between trees or buildings. The WCS and MMDS frequencies between 2.1 and 2.7 GHz are also available to FCC-licensed users. (See IEEE 802.16a)

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Technical FAQ Categories

Basics, Access Point, Antenna Properties, Canadian RSS-210, Client Equipment, FCC Part 15, Point to Multi-Point, Point to Point, Pre-installation and Site Preparation, Radio Propagation, Reference Material, Troubleshooting.