Planning Healthy Comms


It's all very well ensuring the radio path is good but all this hard work will be undone with a badly planned or purchased antenna system. Knowing the signal path is useable is only the first step, ensuring you use it properly is the second.

Antennas, the most misunderstood subject, happens to also be the most important in a radio system. Hopefully the few sections here will help you to choose correctly. Pitfalls are also highlighted, for example knowing the uses of the various types of antennas and ensuring that what you are about to purchase is an antenna up to the job.

Another major stumbling block is coax type and length. All to often the losses of the coax in a system is either over or under stressed. Examples are concern over a 1m piece of RG58 (loss is almost negligible) used on a lightning protection module, yet no concern given to a 30m length (min. 10dB loss) at an obscure site requiring every dB of headroom to ensure reliability. Some sites are going to require long lengths of coax, knowing the accepted losses makes planning the type of coax required a simple task. Using the "Pathloss" Excel spreadsheet will help greatly in ensuring such losses mentioned are given the due consideration they deserve.

A few myths and truths have been included to put to bed certain rumours that have done the rounds.

One facet not often perceived as important is the reduction of "Radio Clutter", this is the energy emitting from a site that is of no use whatsoever e.g. having an omni-directional end-fed dipole on a remote outlying station which then broadcasts not only to the host but in 360 degrees. This drastically decreases the number of systems that can operate on one frequency, and with the licence free bands under such intense pressure reducing the amount of unnecessary radiated energy is to everyones' benefit.

With this in mind all outlying stations, unless there is a chance they may be used as store and forward repeaters, should as a rule be fitted with 6dB Yagis. Some will raise concern over this but when weighed up against the losses in coax, connectors, and general obstructions, it will be noticed there is little gained from the "extra" ERP. If anything, height is the biggest offender of the licence free bands and this is covered in detail in the section "Gain Antennas and LPR". This is also a handy section to read when a path was deemed marginal, with no chance of a repeater, and you want to ensure the path is made as reliable as possible.

Building The System  >>

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