07
Jan
Maintenance Tips for your VHF Antenna 350. In order to get the best long-term performance out of your VHF antenna you need to complete some routine maintenance.
But if youre the crafty type and enjoy a good challenge you may want to homebrew your own antenna.
How long should a vhf antenna be. Choosing the Right VHF Antenna Length Considering how important getting the right VHF antenna length is its no surprise that theres a clear-cut guide for choosing the right size antenna. The wavelength of a signal should always be 14 the length of the antenna youre using as this gives you the very best efficiency. In radio frequency RF terminology the Very High Frequency VHF range is the signal spectrum from 30 to 300 megahertz MHz.
To receive a specific VHF signal you simply need a dipole antenna. Comprised of two lengths of wire or other conductive metal a dipole antennas shape allows the incoming signals electromagnetic field to induce an alternating current AC within the antennas. Remember that VHF and UHF are essentially Line-of-Sight frequencies.
By lowering your antenna it cant see as far. Even if you replace the original antenna with a higher-gain antenna at a lower height that higher-gain signal cant reach as far or receive as far as the higher antenna likely could. Yes you can shorten the cable.
You shouldnt make it less than 1m long and the antenna should be no less than 1m from the radio. How far apart would a vertical HF antenna and a vertical VHF antenna need to be. For example putting a 4080 or 80 at the peak of the garage roof on a mast and a 2m at some point along the roof line.
Distances would be between 10-15 horizontally and 10-15 vertically. Maintenance Tips for your VHF Antenna 350. In order to get the best long-term performance out of your VHF antenna you need to complete some routine maintenance.
Provided you were cautious as to the wiring during installation even the most basic maintenance plan keeps the item good for the long haul. VHF antennas are designed to radiate energy out in the direction of the horizon. To do this they are mounted vertically sticking straight up in the air.
The length of the antenna is related to the wavelength of the transmission. Performance over the same antenna at 35 feet all other factors being equal. A height of 120 feet or even higher will provide even more advantages for long-distance communications.
To a distant receiving station a transmitting antenna at 120 feet will provide the effect of. So how to spot the right VHF antenna. Typically you can choose from one that clouds go on from a range of 10 miles to 25 plus miles.
You also have to consider the antenna height and gain. In most cases communicating by way of VHF is limited to about 35-50 miles depending upon antenna hieght. Sailboats have a distinct advantage here as you can mount an antenna at the top of the mast and reach great distances.
An antenna mounted at 30 feet should have a theoretical range of 778 miles. Of course terrain and surrounding buildings and landscape can greatly affect this number. Antenna height in feet.
Notably since a VHF radio antenna is line-of-sight communication technology anyone trying to communicate with you must be able to see your station for reliable long-range communication. If there are any obstructions between you and another station then the range decreases considerably based on the height of each stations antenna. Antennas can range from a few inches long on handheld VHFs to over 20 feet.
The advantages of a handheld are fairly evident particularly on a smaller craftportability alone being a major plus. However its range will be noticeably and significantly shorter than longer antennas since VHFs are line-of-sight transmitters and so must be able to see the antenna of the station with which they are. On a more serious note it could rescue you from a stranding or accident.
If all things are equal including antenna height and radio model you could go from a range of 10 miles to 25-plus miles just based on the materials in the antenna says Chris Catoe marine sales manager for the Shakespeare Antenna Group. Many authorities on antenna design and installation recommend the antenna should be at least half a wavelength high. This can be relatively easy for frequencies say above 15 MHz or so but for lower frequencies with longer wavelengths this is less likely to be the case.
NMEA recommends 6 feet of vertical and horizontal separation between the VHF and AIS antennas. Most manufacturers recommend more. For example AMEC states in its CAMINO-108 manual the VHF antenna should be placed as high as possible and at least 5 meters away from any constructions made of conductive materials.
There is usually a provision to slide the elements in and out for tuning. If the antenna reads too long adjust the element shorter. If it reads too short make it longer.
Wire Antennas Dipoles and Loops Wire antennas should always be deliberately cut too long at the start. For a typical dual-band base VHFUHF antenna designed for exterior mounting on a structure or mast you can expect to pay from 35 to 300 depending on quality durability and performance factors such as gain. But if youre the crafty type and enjoy a good challenge you may want to homebrew your own antenna.
Answer 1 of 2. An antenna usually 12 wavelength long split at the exact center for connection to a feed line. Dipoles are the most common wire antenna.
Length is equal to 12 of the wavelength for the frequency of operation. We often refer to antenna size relative to wavelength. There are four of them on each side spaced and cut to length to receive the VHF frequency wave pattern.
The four shorter flat plates in front of the long rods is all thats needed for good UHF signal reception. Thats why any antenna smaller than the size of the EZ HD antenna will quickly begin to lose the ability to receive the VHF TV signals. In 1937 the FCC set the standard for AM broadcast antenna radials at 120 each ½λ long at the working frequency.
The traditional belief is the more total wire installed the better the performance especially with poor ground conditions. For some reason it became the norm for amateurs to use ¼λ radials at the antennas lowest frequency.