Campbell Scientific RF401-series and RF430-series Spread Spectrum Data Radios/Modems - Manual (Page 49)

RF401-series and RF430-series Spread Spectrum Radio/Modems
7. Radio receiver is “de-sensing” from nearby transmitter.
This problem can be observed from LED behavior when operating a hand-
held radio near an RF401 or RF430 that is receiving collected data from a
remote station. If you key a hand-held 150 MHz or 450 MHz transmitter,
even though its frequency of operation is far removed from the 900 MHz
band, its close proximity to the base RF401 or RF430 can overwhelm (de-
sense) the RF401 or RF430 receiver resulting in failed packets and
LoggerNet retries. This problem could also occur if your radios are at a
site near commercial transmitters or repeaters. In general it is best to
avoid such sites, especially the high-power FM or AM transmitter antenna
sites which can change at any time with added equipment.
It is possible to avoid de-sensing in some cases if the RF401 or RF430
link is solid enough due to: the proximity of your remote radios; high
antenna gains and directionality; high elevation; and sufficient distance
separation between the RF401 and RF430 and commercial transmitter
antenna. Try horizontal polarization of antennas. A field test in such
situations is essential.
8. There is insufficient signal strength.
There are some things you can try to get that extra few dBs of signal
strength sometimes necessary for a dependable RF link. The drop in
signal going from Winter (no deciduous tree leaves) to Spring sometimes
requires a little more signal.
a. Raise the antenna height using a mast, tower or higher terrain. Often
a little extra height makes the difference.
b. Change to a higher gain antenna
c. If in a multi-path situation such as inside a reflective building or
canyon, try pointing the antenna in unlikely directions while looping
back data (see Appendix K, RF401/RF411 Pass/Fail Tests) from the
remote radio and typing characters in HyperTerminal. Sometimes
a particular reflected signal will be stronger than the direct wave.
d. Change polarization (element orientation) of all antennas in your
network (yagi or collinear) from vertical to horizontal or vice versa.
9. Radios are experiencing interference from neighboring 900 MHz
transmitters.
There are some measures you can take to reduce interference from
neighboring 900 MHz transmitters:
a. Move base station as far as possible from offending transmitter
antenna.
b. Install 9 dBd Yagi and position station so that offending transmitter is
located behind or to the side of the yagi to take advantage of yagi’s
front-to-back or front-to-side ratio (back and side signal rejection).
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