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Rf Wizardry - Part 1

Antenna's, Mounting & Cabling

In this series of technology articles, we talk about Rf systems, where people go wrong and debunk some common rumours for those that say, “it’s the way we have always done it”.  People often call Rf a “dark art”, well I’m here to tell it isn’t and if you follow these simple steps below you will have your systems working more efficiently in no time. 

Poor antenna choice, mounting and sub-standard Rf cabling are some of the most common mistakes I regularly see in the field.  Getting any one of these wrong can seriously affect your system performance, coverage and even compliance.  In this article we unpack all three areas to you give some tools, hints and tips on how to ensure you don’t make these common mistakes.

For rental companies this is particularly problematic as staff movements are high with a large degree of jobs facilitated either in part or totally by freelance operators.  Business owners want to spend the smallest amount for the greatest returns so in some cases choosing kit that serves 80% of your business needs might be the smarter option.  I have also seen a real lack of basic test equipment in the field which makes being the Rf person onsite quite challenging. 

We will cover commissioning and test equipment in another article.

AREA 1: Antenna's

In the holy trinity of Rf engineering, antenna choice is the most important element to “get right” – for if it’s rubbish going in, it’s rubbing going out. When considering what antenna to specify or even deploy, you must consider the application, environment and operating band before making any decisions of what type of equipment to specify.

Application

Will it be used as a receive, transmit or both?

Hint: single carrier setups can often be delivered using a duplexer if you have fixed frequency pairs

Tech Tip: active or passive, filtered or open, repeater or simplex

ENVIRONMENT

Will it be used indoors or outdoors?

Hint: not all antennas are outdoor rated

Tech Tip: weatherproof or not, clean air or lots of Rf

operating band

What are the upper and lower frequency limits?

Hint: wide band antennas can be filtered with little loss to save owning a stack of antennas

Tech Tip: wide or narrow band, multi or single use

AREA 2: Mounting

Next, we consider mounting, again another crucial element in getting your Rf system to perform at its best. Incorrect mounting can affect coverage, performance and safety. Getting accurate information about your proposed installation beforehand will help you make smarter decisions about how and where to mount your antenna.

Coverage

What is my desired coverage area for this antenna?

Hint: higher frequency services react differently to concrete, earth and distance

Tech Tip: Omni or directional, flat or hilly terrain, in building or outdoors only

Performance

How will my proposed location effect the antennas performance?

Hint: height is “generally” a good thing, however might also swamp your antenna if it’s a busy site

Tech Tip: height or low down, what’s in the air busy or clean, filters?

safety

Are there any safety implications to where and how I am installing this antenna?

Hint: build yourself a risk checklist to tick off at survey or install

Tech Tip: risk of lightening, near combustibles or people, access required

AREA 3: cabling

Let’s move on to cabling.  Rf cabling is the quickest way to undo the great work done with antenna choice and mounting.  Put simply, you must use a cable that is fit for purpose for your installation.  How do I ensure that happens?  Well, you consider the following;

operating band

What band will this service operate in?

Hint: build an excel sheet with all the typical cable types on it and how they compare with frequency and distance

Tech Tip: higher freq = higher loss

Power levels

What power levels will this cable need to handle?

Hint: loss also occurs on the receive side, don’t just think about Tx power

Tech Tip: higher power = higher loss

length

What are the lengths of the cable run?

Hint: Consider Rf over Fibre for longer runs

Tech Tip: longer runs = higher loss

As you can see from above, all 12 questions are in some ways interrelated so must be considered as a solution and not just individual elements. The cable choice you make can affect what amount of antenna gain you need. The distance between antennas can drive the need for more accurate filtering, and a busy Rf environment will affect where and how you mount your antennas.

These 12 Rf System tools, tips and hints mentioned above are designed to give you a picture of what you are trying to achieve. It is drawing out the responses that will drive us towards certain equipment choices, and whilst there are many other components to an Rf system these are the keys areas you “must” get right, as they are the building blocks to your foundation!

In our next article we will focus on the grout between these blocks covering, filters, power dividers and combiners, and commissioning. Our third article and final article in this series will cover test equipment and compliance detailing where best to spend your money and how you can ensure you are operating within the limits of your licensing conditions.

About Me

I am a qualified Rf Engineer with over 30 years’ experience in the broadcast, entertainment and live production worlds. Having worked all over the planet on multiple Olympics, Reality TV shows, and live events; my career has been one loaded with lots of opportunity, technology and travel. 

Now I own and run D2N, a boutique Communications and Audio solutions company focused on solving technology challenges for my customers. I am also an accredited ACMA licence planner so can advise and issue licences for a range of services including land mobile (two way radio), broadcast, and satellite communications.

Visit our website for more in-depth product information, www.d2n.com.au

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