The Spectrum Analyzer is found in the Text interface (either via Telnet or a serial port configured for
Text Interface capability), which provides live updating. It is found in the Configuration menu, rather
than the Diagnostics menu as might be assumed, because it provides the ability to change the radio’s
configuration by locking out channels.
|CAUTION: It is strongly recommended that the system’s Access Point radio be powered off during|
Spectrum Analyzer testing. If the AP is still running the Spectrum Analyzer will not be able to
differentiate between desired signals from the AP and unwanted signals from interference sources.
Level: The vertical axis of the graph represents the strength of the signal or noise heard by the
radio while running as a spectrum analyzer. It is measured in dBm. (decibels relative to a milliwatt) A
level of -120 can only be attained by attaching a dummy load to the radio. -105 or -110 may be heard in
a very quiet location. A -40 dBm signal is very strong, eg from a radio very near. Any signals not from
your own radio system should, on average, be lower in strength than signals from your own system.
The horizontal axis represents the channel number. In the FCC/IC version of the 900
MHz radio there are 67 channels, numbered from 0 through 66. Other radio types may have a different
number of channels.
Shows the number of locked out channels. If any channels are constantly interfered with
(eg cellular or paging systems, or government systems) the user may lock out channels so they are never
used. This is NOT recommended for normal interference types, as such interference moves constantly.
In the 900 MHz FCC type radio, up to 14 channels may be locked out. Other radio types may allow
locking out of a different number of channels.
The vertical bars seen on any channel (eg “|”) represent the signal level heard on the
last sweep. Go to the top of the bar, then across to the signal level on the left to see how strong the
Upwards-pointing arrows, called carets (over the 6 on your keyboard), may appear
above the vertical bars on some channels. These represent the strongest signal heard on a specific
channel since a continuous sweep began.
If after extensive testing it is found necessary to lock out channels due
to persistent interference on specific channels, here is the procedure:
- Log on to the radio locally with a text interface (either Telnet or serial)
- Go to the Configuration menu, then select the Spectrum Analyzer
- Using the arrow keys, move left or right to select a channel to lock out
- The selected channel number is displayed at the top of the screen, and a caret (^) along the horizontal
axis below shows the channel selected
- Press E to set a lockout channel once you have moved to it, or G to begin selecting a range of channels
- See the note at the top stating “Lock out x more channels for valid configuration” In the 900 MHz FCC
version, you must always lock out 6, 8 or 14 channels.
- If you want to remove the lock-out of a channel, move to it and press F
- Once you have locked out the required channels, press [Esc] to go back to the Configuration menu
- Activate the changes to the radio by pressing I
- If you want to save the radio’s configuration (including the locked-out channels) open a web browser
session with the radio, go to Setup, then Save/Load and save the file. (wait until activation is complete)
|Important Note: The locking out of channels is only helpful in certain circumstances, when|
interference on specific channels is proven to be continuous. For example, a nearby cell tower causing
noise on the lower group of channels. Often however a good band-pass filter can block such out of band
interference. (eg Microwave Filter Company’s model 17965) Normal interference from other frequency
hopping radios or electrical equipment will typically drift from channel to channel, so locking out
channels has no effect.