Specifications

environment. The alignment of the antennas was done by first using a visual alignment and then
fine-tuning by using the built in buzzer in the transceivers. Aiming proved not to be critical, as
the small changes in angle did not change the received power level much since the beam pattern
is relatively flat. The range as given by the user interface of the Redline terminal was 17.03
miles.
The severe difference in throughput in different channels shown in Figure 5.8 may have been due
to the presence of interfering signals. The signal propagation should not differ significantly
between the different channels. The possibility that additional noise, such as local microwave
radiation from other users of the same spectrum, which might be contributing to the lower SNR
was explored. An RF spectrum analyzer was hooked to the antenna at the Cobleigh Hall site to
look for sources of interference, and to measure the noise floor. The noise floor was observed o
be at about –100 dBm. There were two narrow band interferes noted to be present. Their
characteristics are shown below in Figure 5.9. There is a possibility that there was an interferer
present at the remote site that could not be seen at the Cobleigh Hall site. This would impair the
link, yet not be detectable from the Cobleigh Hall site.
Frequency, MHz Power level, dBm Channel
5764.6 ~-90 2A
5821.8 ~-91 5
Fig. 5.8 The two interferers present at the Cobleigh Hall site.
Channel Throughput (Mbps)
2A 20.06
3 19.87
4 13.09
4A 13.14
5 11.05
Fig 5.9 The effect of utilizing different channels
29