HopNet RS-232 Serial ModBus Radio
Guidelines for Avoiding Terrain Obstructions
The HopNet transceivers operate in the 2.4 GHz frequency band. While this band
offers many advantages over the VHF band for data transmission, it is also more
prone to signal attenuation from obstructions such as terrain, foliage, buildings and
anything else in the transmission path.
Use the following guidelines to avoid terrain obstructions:
•
A line-of-sight transmission path between the base and the associated remote
sites provides for the most reliable transmission path.
•
A line-of-sight path can be achieved by mounting the station antenna on a
tower or elevated structure that raises it to a sufficient level to clear
surrounding terrain and other obstructions.
•
The importance of a clear transmission path relates closely to the distance to
be covered. If the system is to cover only a limited geographical area such as
1-3 miles, then some obstructions may be tolerated with minimal impact.
•
For longer-range systems, any substantial obstruction in the transmission path
could compromise the performance of the system.
RF Tools
Range Optimization.
On the RF Tools tab in the HopNet Configuration Wizard,
the Range Optimization function is used when the HopNet radios will be covering
ranges of more than one mile. The distance optimization parameter is needed to tell
the radio when to look for the acknowledgement from the receiving radio. This
function will automatically detect the best setting for this parameter and save it in the
radio. The value is only required in the remote radio and not the base. Different
remotes at varying distances from the base will have different values for this
parameter. This function can take several minutes to complete.
Receive and Bi-Directional Transmissions
. The Receive Only function
displays the percentage success rate for receiving transmissions from the base. This is
an indication of how well the remote HopNet “hears” the base. The Bi-Directional
function provides a round-trip success rate. That is, the base must successfully receive
data from the remote and the remote must successfully receive data from the base. In
theory, this percentage should be the square of the Receive Only percentage. If it is
substantially less, it is an indication that the base HopNet is having difficulty
“hearing” the remote. Good RF links will have the Receive Only percentage above
95% and the Bi-Directional percentage above 90%. These functions operate with the
Automatic Retransmit Request (ARQ) disabled and as such provide an indication of
link quality but do not provide an indication of how often data will get through since
in normal operation ARQ is enabled and the radio automatically and transparently
will resend data that was not received on the first attempt.
©
2000- 2004 Cirronet
™
Inc
52
M-2410-0022 Rev B
