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FM Broadcast Antenna Installation Tips.

 

Tip one is safety first. If this is the first time you're installing an antenna take a good look at the location you've picked. Run the entire installation through your mind step by step before you put yourself in any risky situation. Think of all the materials and tools you'll need and the position you'll be in while using them. If you're not completely comfortable with these thoughts, hire a professional High Rigger. This is one of the easiest antennas you can install but the high locations that work best for FM coverage are where the dangers arise.

 

Look up for overhead wires. If there are any within possible reach of the mast, tower, guy wires or antenna being planed, change the location. The NWE-34 FM Broadcast Antenna is DC grounded for the best lightning protection however, this can kill you if the antenna comes into contact with power wires while you're touching the mast or tower. If at any time you feel like you're loosing control of the antenna, let go while pushing it away from you. It's not worth the few hundred dollars because the risk of serious injury increases exponentially immediately after making the wrong decision in these cases.

 

The "Transmission Line" or coax cable you use does make a difference. Poor quality cables will waste RF power due to excessive loss within the cable. They can also leak power out of the cable though insufficient shielding and cause interference to other equipment around the site. In most cases LMR-400, LMR-600 or LMR-900 is acceptable. The different types are dependant on the power level and length being used. If the installation is on a shared tower where your transmission line will be parallel to others, use Hard-line cables because they are the best at maintaining isolation in these applications.

 

We've had some customers mistakenly install an RF Choke on the transmission line assuming that since it was an End Fed design it may have Common Mode Current problems. Generally speaking, this is a good idea but not once you understand the design of this antenna. Unless this antenna is grossly mis-tuned in terms of impedance or resonance, there is virtually no CMC generated. Any residual currents are radiated off the outside of the cone in a constructive phase. This phasing is a result of the Collinear action taking place within the cone. Adding a choke can cause serious problems with the antennas pattern if the choke happens to be resonant.

 

Since FM signals in the VHF spectrum propagate with "Line of Sight" coverage, the higher you can legally place the antenna, the more range your station will have. Installing any FM broadcast antenna on top of a metal roof or large metal surface can be problematic. If you install an antenna closer than about 25 above a metal roof, it will push the radiation pattern upwards and away from the distant horizon. Conductive Guy Wires that are used on telescopic masts should be no closer than 10 feet to the base of the antenna for the same reason. If you use a telescopic mast, only purchase a heavy duty version so that the top 10 feet can be free standing with this light weight antenna.

 

We also have to consider new safety regulations dealing with long term RF exposure levels. The more power the station has and the closer the antenna is to people, the higher these risks become. The immediate location around the antenna should be above any living spaces or place where people will be for extended periods. Without examining a specific site, only basic guidelines can be given here. These are estimated heights and distances for safety that relate to radio frequency exposure. More height or distance improves safety. More height improves safety and coverage.

 

At power levels around 25 watts or less, just get the antenna 10 feet or more above people within 100 feet of it. At the 200 watt level this should be increased to 20 feet above people within 300 feet. At 1000 watts it should be approximately 40 feet above people within 500 feet. At 3000 watts the height should be around 50 feet above people within 750 feet of the antenna. These estimates can not be guaranteed in every installation. Some may require more separation while others can require less. When in doubt increase distances or measure field strength in areas of concern for verification. Vertical height is more effective than horizontal separation here.

 

It's always easier to order your antenna factory tuned to your frequency. Then all you do is adjust the top 1 inch diameter telescopic section of the antenna to the black line and you're done. Since this is not always possible we supply easy tuning instructions with your antenna. No meter or special equipment is required. Just a tape measure and the tuning chart are all that is needed for excellent results. This is due to the fact the NWE-34 has a much wider bandwidth than most "tuned" antennas.

 

The bandwidth is wide enough that several sites are using one antenna with multiple transmitters feeding the antenna on different frequencies. At one installation we have 3 transmitters all operating into a single 3kw NWE-34 antenna with two of them being separated by 2.8 MHz. For most users, this basically means the tuning of the antenna can be off a considerable amount before it would cause any noticeable performance issues. This is also beneficial when bad weather arrives. In torrential rain, snow or ice loading, many other antennas can be de-tuned to the point where these conditions shift their resonant frequency outside of their bandwidth and require expensive radomes to prevent it.

 

If there is any chance a lightning storm is going to pass over your antenna while it's installed, you'll have to ground it. Don't overlook this step or take short cuts here. If you do the job right, you may never know the station was hit by lightning because everything keeps right on working like nothing happened. If you do it wrong you may never know you got hit by lightning either, because all of the equipment and anyone too close to it may be toast. I've seen "Ball Lightning" jump out of the corner of an ungrounded piece of equipment and roll across the concrete floor untill it found a radiator it liked.

 

Since this antenna has been designed with a very substantial DC ground path that is isolated from the ungrounded conductor of the transmission line, all you need to do is connect a suitable ground wire directly to one of the nuts on the antennas lower mounting U-Bolt. The wire should be no smaller than #6 and make a straight path down to the base of the support structure where it connects to its own 8 foot ground rod. If the wire must go around corners, bend it into an arc rather than a 90 degree corner.

 

Do not just ground the base of the mast or tower. How much rust or corrosion in their joints is needed before the resistance becomes higher than the shield conductor on your transmission line? Lightning is going to take the path of least resistance. Make sure that is where you want it to go. Some alternatives are to bond all of the mast or tower sections together using copper strap and clamps or to install a grounding block in the transmission line at the tower base. Adding this type of grounding block before the line enters the building is always good practice. If the tower or mast is away from the building, burry the line when possible. This will add another layer of protection through capacitive coupling to ground.

 

Some installations will require the antenna to be side mounted off the face of a tower. In these cases the center of the antenna should be the standard 1/4 wavelength distance off the face of the tower. The antenna should be positioned on the side of the tower so that it blocks the antennas view in the direction where distant coverage is of least concern. Tessco sells a wide assortment of 36 inch side mount brackets that work well in most applications. Although, you can make one out of a few pieces of heavy duty angle aluminum for a fraction of the price and you can match your wavelength perfectly. If it can support a moderate to large residential TV antenna it will support this 8 pound antenna.

 

When side mounting this antenna to a tower, the tower should extend past the top of the antenna by at least 10 feet. This is to keep any reflection angles off the tower symmetrical above and below the antenna. Failing to do this will cause one side of your radiation pattern to tilt downwards in the direction of the missing tower length while the opposite side tilts up. The end result is the pattern will no longer line up with the distant horizon. If the antenna is mounted on a tall buildings roof and this roof has a large surface area, the antenna should also be high enough above the roof so that its edges do not block the antennas line of sight to any desired locations.

 

Like any other FM broadcast antenna, the NWE-34 can be combined together to form a multi-bay stacked array with a doubling of gain each time the number of antennas phased together is doubled. Because this antenna is longer than other FM antennas and already has more than one point of radiation, the vertical spacing on the tower should be 1/4 wavelength more than the common 1 wavelength spacing. That means the base of one antenna (or any same point on the different antennas) is located 1.25 wavelengths away from the exact same point on the antenna directly above or below it.

 

My last bit of advice on this topic is do not perform antenna installation work alone. Even if the job is simple like this antenna can be, unexpected things can happen that may prevent you from getting help yourself if needed. You should at least have a second set of eyes supervising and able to assist if something goes wrong. In the event of electric shock, do not touch the person or any metal they are in contact with at this point. Pry, push or pull them away using something non metallic or not conductive that is completely dry to stop the shock and dial 911 immediately.

 

   

   

 

 

 

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