Codan Radio Radio Repeater Systems Training Guide - Manual (Page 15)

RADIO REPEATER SYSTEM | TRAINING GUIDE
Chapter 1: Repeater System Basics Page 7
The propagation of radio energy from one point to another is affected by obstacles, both natural and
man-made. Much depends on whether the obstacle is totally blocking, or partially blocking the signal
path. In the latter case the refl ected signal from the obstacles takes a longer time to reach the receiving
antenna than does the direct ray. The result may be distortion, or even total cancellation, of the received
signal.
Appendix C details the method of calculating the path loss between sites. Once the path losses are
known, simple calculations of losses and gains will provide the signal level which should result on the
paths. Appendix D contains instructions for calculating the signal level on a path. Recommended
signal levels on your paths are suggested as follows:
i) between repeater sites - a minimum of 20 μV.
ii) repeater site to base station - a minimum of 10 μV.
Discussion with other local users and a trip to the proposed site may also be advantageous, particularly
if you also do some tests using a low-powered portable (at the proposed site) to a mobile in the
questionable areas. See instructions in Appendix E on mobile coverage tests.
There are other items for consideration, many other factors that are not easily measurable may affect
radio signals. Signals may be received beyond line-of-sight, and some obstructions may not completely
wipe out signals. On longer paths, you may also gain the advantage of refractive bending of the signal
beam which is allowed for by your use of 4/3 earth curvature graph paper. Note however, that as the
frequency is increased; refractive bending, although normally downward, will vary (even upward) by
atmospheric conditions such as temperature, pressure and relative humidity. At VHF and UHF below
800 MHz this is not normally a problem, although other weather conditions such as heavy sleet or ice
storms may reduce your signal levels by up to 20 dB.
Licensing your radio system for use does not automatically give you the legal authority to install equipment
on site. Leasing or buying the small plot of land is required. You may fi nd it necessary to work with
different governments (federal, municipal, county, state, etc.) to arrange all of your requirements. Most
authorities have additional specifi cations that you must meet if your repeater sites are within a specifi ed
distance of an operating airport. Painting and lighting of obstructions is one such specifi cation.
Equipment outages at a mountain top environment are often weather related. The equipment is
designed to be as reliable as possible and is thoroughly tested before installation but a lightning strike
nearby can negate all of that in an instant. Consider carefully before locating your repeater site on a
Lightning Peak, or; as we have done in the example, on an Iron Mountain. If not familiar with weather
patterns in the area yourself, talk to those that have local knowledge.