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Basics of cable/antenna test tools for base stations

Posted: 19 Nov 2014     Print Version  Bookmark and Share

Keywords:mobile communication network  base stations 

Distance to Fault (DTF): This can be of great assistance in locating the positions of discontinuities and shorts in the base station antenna/cabling that have led to VSWR or return loss issues occurring. Normally complex Fast Fourier Transform (FFT) algorithms are employed by the analyser to translate acquired frequency data into the time domain data, so that signal aberrations can be ascertained in relation to distance.

Other important factors
As well as supporting all the previously mentioned measurement modes there are a wide variety of different features and functionality that are offered by antenna/cable analyser models currently on the market which may prove to be beneficial. Here are just a few major ones.

Obviously, since these instruments are being used in the field and need to be carried up antenna masts, etc., a lightweight, portable format is highly advantageous. Normally an overall weight below 3kg and dimensions of around 200mm x 280mm x 150mm would be expected. Other characteristics like long battery life and robust construction are also elementary.

To make the examining of acquired data as simple as possible to execute, a unit with a relatively large (+7" diagonal), high resolution colour display should be sought. Inclusion of a touch screen has almost become ubiquitous now – this leads to a more intuitive user interface which is easy to operate, however it is worth pointing out that potentially there can be drawbacks associated with touch screen operation. If an engineer is up an antenna mast and is wearing gloves, then a touch-enabled user interface can become difficult to manipulate.

Another feature, which is available from some manufacturers, is the ability for engineers to write their own test procedures for controlling the instrument. This allows a company to guarantee that every one of its field engineers is following exactly the same procedure when testing a specific base station. This reduces the possibility of errors occurring – such as selecting the wrong the frequency when testing.

It is likely that two port transmission measurement will prove itself to be useful, as it will lead to results that are more accurate than those from single port measurements. 3G/4G base stations today use diplexers and duplexers to increase cell coverage. Via two port transmission measurement it is possible to carry out gain, isolation and insertion loss measurements to deal with this. Furthermore if the analyser has a split screen facility, the user can examine two different measurements (such as DTF and VSWR) at the same time.

Access to superior accessories to accompany these analysers is also important. For example, low loss cables and probes with mean that more accurate test data can be acquired. Furthermore by utilising precision calibration kits, that need to be maintained in good order and regularly recalibrated themselves, it can be ensured that the instrumentation fully complies with all the relevant standards throughout its operational life. There is thus a direct correlation between the quality of the measurements taken and the quality of the calibration kits.

So that more can be done with just a single item of equipment, additional functions may be integrated into unit. Spectrum measurement, for example, can be of use as it allows sources of interference to be determined. As a result more advanced models will often incorporate a spectrum analyser. Increasingly network operators will expect field engineers to accurately log the position where testing was undertaken, so GPS is becoming an important supplementary feature. Furthermore, passive inter-modulation (PIM) is now regarded as one of the critical phenomena that needs addressing when base station infrastructure is being deployed. Some analysers now also have the capacity to provide a basic indication of the presence of PIM, though utilisation of a separate dedicated PIM tester will be needed to scrutinise it properly. The detailed mapping out an interference profile, using a directional antenna, can be beneficial to the field engineer, so units that provide this facility are likely to be very attractive.

In many cases analysers are only required for short periods of time. This means that it may not be economically viable to purchase such items of equipment. Instead, in many cases, it will be more attractive, both technically and financially speaking, to partner with an equipment rental firm. Among the products in test sourcing specialist Livingston's portfolio that are widely used in antenna/cable analysis are Anritsu' Site Master, JDSU CellAdvisor and the ZVH from Rohde & Schwarz. These are offered with a full range of accessories, plus a comprehensive calibration management service. The flexibility that this sort of engagement permits means that as well as having complete control of how long the analyser is kept in use (so that the monetary investment matches well with the revenue generated), different analysers options can be tried out. If one analyser model proves to not be as suitable as first expected, then an alternative can quickly be sought without any cost penalties being accrued.

About the author
This article is contributed by Livingston Ltd.

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