How do I calculate
my network link budget?
You should perform a network link analysis for every Point
to Point link, and for a sampling of your Point to Multi-Point
links. The analysis should be calculated for both signal directions.
There are many online calculators for link analysis. Some
of these are Wireless Network Link Analysis from Green Bay
Professional Packet Radio, Wicklewood & Wymondham Calculators,
and RFProp Software by Colin Seymour G4NNA . A basic explanation
of link budget calculations can also be found in a white paper
from Intersil. 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 wireless 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 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 wireless 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 wireless
access point 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 directional 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 directional antenna at the 100 foot level, you will
have to attach the omni directional antenna 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 directional
antenna is parallel to the tower legs at all times.
How do I perform
a Point to Point wireless 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 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 a wireless access point 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 wireless spectrum analyzer and both vertical
and horizontal polarized antennas. If you have Teletronics
radios, here is a neat wireless site survey tool. There are
also professional consultants (e.g. Cyber-Doctors) that can
perform wireless site surveys for a fee. Wireless 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, RP-TNC, SMA, RP-SMA, MC-Card,
and MMCX. 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
wireless 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 wireless 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 wireless 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 wireless antenna before and after installation?
The VSWR (Voltage Standing Wave Ratio) of a 2.4 GHz wireless
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
and Bird Electronics. 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 WLAN expert also
has VSWR measurement capabilities for PRISM chipset-based
cards. Wireless 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 wireless antenna before installation,
make sure that the wireless 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 wireless antenna manufacturers spec their wireless antennas
for either 1.5:1 or 2:1 across the bandwidth.