INSTALLATION
Power Supplies :
As with any radio communications system, the RTcom modem should be connected to a clean and stable
supply. Switch mode power supplies are rich in RF harmonics and should not be used. Please note that in
many cases, a CE sticker on a power supply is insufficient protection against potentially damaging
harmonics. The reality is that the EMC pass limits are set at only -57dBm (31uV), whereas a radio is quite
capable of operation down to and beyond -115dBm (0.5uV). Hence, a power supply is capable of legally
generating harmonics quite capable of blocking a radio modems operating channel.
As a word of warning the frequency of the offending harmonics can shift with both ambient temperature,
time and power supply load. Please do not be fooled into thinking that a system is operating correctly.
There has been a number of reported cases of radio blocking due to power supply switching frequency
variations. Hence, as a rule of thumb, we only recommend the use of linear power supplies. Similarly
w
here supply interruption is to be protected against, we recommend the use of float charged batteries
(12V or 24V dc) and not switching UPS’s.
Location :
For indoor installations, we recommend that the modem is located away from sources of heat and electrical
apparatus such as Inverters. Care has to be taken to minimise cable lengths both with respect to the
antenna location and the attached terminal equipment. Generally, RS232 should be used for short distance
links < 30ft (10m) and RS422 / RS485 for long links of up to 1000ft (300m). In practise, the maximum
distance achievable will depend upon the combination of the drive capability of both modem and data
terminal.
The IP-65 rating of the modem enclosure would to many imply that it could be operated outdoors in all
weather conditions. Experience has shown this to be true, but operation can be jeopardised through long
term exposure to rain, frost, direct sunlight, and blown sand. For these reasons, we also recommend,
where possible, the modem should be mounted within a second enclosure of a similar IP rating and where
the climate is variable, a thermostatically controlled anti-condensation heater be used. This practise has
been used by our own field service engineers for many years and has proven very successful.
For battery powered operation in cold damp climates, the only reliable way to achieve long term operation
is to use double IP-65/7 enclosures, with both the outer and inner enclosure fitted with silica gel desiccant
sachets.
Please be aware that solar heating and wind chill can take the modem beyond its designed operating
temperature range. Further, thermal cycling can encourage moisture ingress due to pressure changes.
Whenever necessary, please fit your enclosure with wind deflectors and/or sunshades.
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