We are witnessing an increasing number of outdoor deployments of antennas for M2M applications including security and CCTV systems, utilities, telemetry and monitoring and installations on roofs, walls, cabinets and other street furniture. These applications are using many frequencies including 4G, 3G, LTE, GSM, WiFi / WLAN, 433 MHz and other ISM bands. There are also a wide breadth of antenna choices and we often see that many customers are unsure of what to consider when deploying antennas outdoors. So through this article we would like to give you some key points to consider.
Mounting:
One of the first questions to look at is where and how you are intending to mount the antenna. Some mounting methods are more likely to pose challenges in terms of weatherproofing that others.
Outdoor can have two interpretations - either the antenna is fully exposed to all elements or that the antenna is outside, but in a protected position. The position of mounting should have an influence on the antenna selected. If the antenna is fully exposed to all the weather mother-nature can throw at it, then the quality of the antenna materials should reflect that - i.e. fibreglass or UV-resistant plastics/sheath and weatherproof metal parts that will not oxidise or rust and also high quality accessories - mounting brackets, clamps, cables and connectors.
Antennas can be independent components such outdoor antennas for pole or wall-mount when usually as long as they are of quality construction and fully sealed then the bases are covered. When the antenna is cabinet, enclosure or street furniture mounted, then there is a point where the installation can become compromised.
For through-hole mount antennas, typically you have to drill a hole in the mounting surface and the antenna will have a stud (or hollow boss) through the middle of which the antenna cable exits. The antenna stud is placed through the hole in the mounting surface and there is a nut that is screwed onto the stud from underneath (the mounting surface) and holds the antenna in place. It is important to check the quality of the stud-nut combination. A weak stud and nut configuration does not lend itself to longevity. In addition, most quality antennas will have a thick, durable gasket sitting under the antenna so when the nut is tightened there is a really watertight seal where the antenna mounts. If the stud-mount antenna does not have a gasket or simply a meagre one, best to leave well alone. As a belt and braces approach, some installers add a thick layer of Mastick (waterproof bond) between the gasket and the mounting surface - this provides an even more durable seal to ensure absolute water tightness.
Materials:
In the selection of the antenna, it is wise to understand if the radome, sheath, body and other antenna material is suitable for long term outdoor use. As mentioned previously, fibreglass or expressly UV-resistant materials should be used. There is nothing worse than purchasing an antenna with a white radome that yellows after a short time mounted outside. Also in terms of the mounting brackets and clamps, ensure that these are galvanised metal or made of materials that are not going to corrode or rust.
Sealing/Bonding:
Time and time again we come across customers who have used low cost antennas outdoors and discovered to their cost that the antennas are very lightly glued or badly bonded and within a very short period of time the antennas are suffering an ingress of moisture or worse still the sheath or radome has become detached from the antenna body. This has two costs - one is the cost of a replacement antenna, second is the cost of second site visit which usually ends up costing way more than 10 antennas in the first place! We suggest you do check how well the antennas you intend to use are sealed and bonded and whether they are robust enough to withstand long term outdoor deployment.
Connectors:
The choice of connectors is also critical when deploying outdoor antennas. Standard M2M connectors such as SMA or FME aren't bad, but definitely fall behind N-Type or TNC connectors when considering outdoor RF installations. The N-Male / N-Female and TNC-Male / TNC-Female connectors might be larger than SMA or FME, but they are a lot more robust and can tolerate more abuse! Also it is worth considering the type of panel-mount or bulkhead connectors you intend to use - make sure you select a panel mount connector with an O-Ring so, for example, when you mount the N-Female Bulkhead Jack against the inside of an enclosure there is a rubber O-Ring sitting between the flange of the bulkhead connector and the enclosure making a nice tight seal protecting against the ingress of moisture.
Accessories:
As a rule of thumb, M2M antenna deployments are only as good as the design, the products, planning and installation. This also should include the accessories - waterproof tape, waterproof bonds and sealants help to make a good installation better. There is nothing wrong with covering an installed coaxial connector with waterproof tape to help ensure longevity. Also when deploying other products in the installation - surge protection, splitters, RF cable etc. do make sure these are designed into the installation effectively so they do not introduce a point of failure/weakness into the otherwise weatherproof installation.
We hope the above considerations will aid you in the design of your outdoor installation and the selection of the appropriate antennas and associated products. We wish you a successful deployment.
