RTcom Radio Modems - Manual (Page 7)

7
For battery powered operation in cold and damp climates the only reliable way to achieve long term
operation is to use double IP65/7 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.
Antenna Feeders:
The basic rule of thumb is the longer the cable the greater the loss. Always attempt to keep cable runs
to a minimum and whenever possible uses the lowest loss cable available. Both cables and
terminations should always be 50-Ohm impedance. Cable bends should no be too tight i.e. the radius
of the bend should be greater that 10 x the diameter of the cable.
It is important to remember that coaxial cables have losses proportional to their length and quality.
The following table gives loss figures from typical popular 50-Ohm coaxial cables: -
dB Loss per 10m length
Cable Type Dia 100MHz 1000MHz
RG58 5.0 2.0 7.6
URM67 10.3 0.68 2.52
URM76 5.0 1.6 5.3
Our modems are normally supplied with N-Type terminations (sockets). Other terminations (BNC or
TNC) can be supplied to customer specific orders. Generally we find the N-Type to be the most
reliable, robust and readily available connector that can accommodate low loss cables such as
URM67.