The antenna is the most important part of the transmission system and must be correctly installed before proceeding further and before any transmission equipment is connected.
Under no circumstances should the antenna be mounted and used at ground level or within a few meters of personnel.
Ideally this antenna should be mounted at least 20 meters high and clear of any surrounding objects to get maximum range and more importantly to reduce risk of radio frequency radiation to personnel. When mounted at least 20 meters in height off ground and using 400 watts of transmitter power, power flux density measurements made at ground level directly under the antenna show less than 1 W/m2. Several European countries use a value for the power flux density of 10 W/m2 as a basis for considering whether or not an area is safe. The issue of radio frequency radiation limits is a contentious one and work in this field is continuing worldwide.
You are responsible for selecting the correct antenna for your application, installing it properly and ensuring the system maintenance.
This antenna is intended for use with an FM broadcasting transmitter up to 400 watts at a permanently pre-defined location with a license or authorisation from the radio spectrum regulator of your country.
|PVC insulation tape and/or Self Amalgamating Tape|
|Tape Measure with mm|
|A secure mounting mast or pole with a diameter of 45-50mm and a vertical space or length of at least 8m|
|Antenna 50 ohm feeder cable, normally this is LMR400|
Following is a list of precautions to follow when installing the antenna if placement of antenna and cables is anywhere near power lines.
|Erect antenna on side of house or building as far away as possible from the power line.|
|Avoid crossing antenna cables under electrical power lines.|
|Do not attach antennas to towers, poles or similar structures carrying electrical power lines.|
|If you are not experienced in installation of antennas, have experienced persons assist you.|
|During installation, tie off antenna with rope so if it falls it can be diverted away from power lines.|
|Avoid fastening antennas, especially self-supporting types, to old chimneys or to any chimney not designed to take such stress. Forces created by a strong wind may be sufficient to topple both chimney and antenna.|
|Make sure antennas have been properly grounded and provided with other necessary lightning protection.|
|1||A Dipole (YELLOW marked cable + 0.63 cm RG11)|
|1||B Dipole (RED marked cable + 0.63 cm RG11)|
|4||C 66cm radiator rods|
|4||D Bolt, wing nut and plastic spacer|
|1||E Splitter box|
|2||F Mast fixing clamp|
|10||G Cable ties|
UNDER NO CIRCUMSTANCES should the antenna be mounted and used at ground level or within a few meters of personnel.
Ensure that all antenna connections to the transmitter or power amplifier are sound, this is important as poor connections and soldered joints can cause RF burns to personnel, severe noise to the transmission and excessive RF bandwidth.
1. Mount the tuned dipoles to the mast using the clamps provided. It is IMPORTANT for correct operation that the dimensions on the diagram are followed as closely as possible, all dipoles must be directly above each other and the 'terminal box' must be facing the same way for the system to work properly and give full tuned bandwidth from 88-108MHz.
2. Mount the splitter box with the three RF connectors using the tie wraps provided on the mast between the dipoles as shown on the diagram. The splitter boxes are marked top and bottom, make sure top is facing upwards. This is because the plastic enclosure shelters the internal connections from rain and water
3. Connect the main feeder cable from the transmitter to the CENTER connector of the splitter box.
4. Connect the Top dipole to one of the OUTER connector the splitter box using the cable marked in YELLOW. Connect the Bottom dipole to the remaining OUTER connector the splitter box using the cable marked RED. There will be excess cable, simply coil this neatly and tape or tie it to the mast (DO NOT CUT IT BACK AND REFIT THE PLUG). The cables marked with YELLOW and RED of each dipole are critical phased lengths and must never be altered in length.
5. Wrap PVC or Self Amalgamating tape tightly around and all over the plugs on the Splitter Box to waterproof them.
6. Securely fix the cables using PVC tape or large cable ties to the mast as shown in the diagram opposite. Make sure the cables are not going to flap around in the wind.
7. Make sure that all fixings are tight and are not going to work loose over time with wind.
When writing this manual there was no EU directive regarding the EMC (Electro Magnetic Compatibility) of Band II VHF broadcast antennas, however in our view there are some potential EMC compatibility issues that need to be addressed when installing this antenna system. On completion of the antenna installation check;
1.All the cables entering the connectors are tight and properly crimped or soldered
2.All the connectors are screwed in tight and sound.
3.PVC insulation tape and/or self amalgamating tape are wrapped around all the connectors to stop water entering the connector and the inside of the body of the cable.
If any cables are loose or there are bad connections this can cause some non-linear resistance, diode action or some small arcing. When this happens it creates EMC disturbance (arcing and crackling sound) across a wide frequency spectrum.
|Gain||4.8dBi at 98MHz (EIRP = 2.3 x TX power)|
|Freq Range||87.5 to 108 MHz|
|SWR||less than 1.6|
|Max Power||400 Watts|
|Construction||Aluminium and Plastic (ABS)|
|Connector||N type Female|
|Input Z||50 ohm unbalanced|
|Vertical Beamwidth||32 Degrees|
The diagram above is the E-Plane radiation pattern. Stacking two dipoles this way with spacing of 1.9 metres gives a gain to the horizon of about +4.8dBi. Each dipole is tuned to give 50 ohms at band centre of 97.5 MHz. The two 50 ohm dipoles are combined together using two ¼ wavelength 75 ohm cables, this configuration is known as the Wilkinson combiner. At the point where they are combined the impedance is near to 50 ohms. This results in a maximum SWR of 1.5 continuously from 87.5 to 108 MHz without any tuning or retuning
Because antennas are passive devices maintenance requirements are low, however don’t accept low as being none existent, some periodic inspections are required.
Always following a heavy storm or extreme weather condition an inspection should be done and as shown in the table below.
|WEEKS||Building Roof||Light Duty Tower||Heavy Duty Tower|
We sell this equipment to professionals and organizations in good faith it will be used correctly and legally. Most countries in the world require licensing for this antenna to be used with a transmitter. It is the customer’s responsibility to check relevant laws, directives, regulations and licensing requirements before putting this product into service with an antenna system. You, the customer or user agree to defend, indemnify and hold harmless Aareff Systems Limited, its employees and agents, from and against any claims, actions or demands, including without limitation legal and accounting fees, alleging or resulting from improper or unlawful use of this equipment.
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