When you are installing your VHF, arguably the many crucial consideration is wright here to area the antenna. You recognize it should be as high as feasible, however mounting it high introduces difficulties in the installation itself bereason it is harder to obtain to. 
Inevitably, this leads to you questioning whether it really is that vital to mount the antenna up high.

You are watching: Eq-20 why is the height of a vhf radio antenna important?

The elevation of a VHF radio antenna is crucial because VHF is thought about a “line-of-sight” interaction modern technology. Basically, you have the right to only interact in between two antennas that are within sight of one one more. The greater each antenna is, the further you can connect.It is most basic to imagine by considering exactly how far you have the right to check out. If you are standing on the ground, you have the right to only view a short distance. From the peak of a building, or a hill, you can watch considerably better. This is your line of sight.VHF radios work in the same means. Their signal is transmitted out of their antenna and also travels in a directly line. If there is an additional antenna within sight, it will obtain the signal.
An antenna placed on the ground has a shorter line of sight than an antenna high up, placed on the top of a structure or at the top of a mast on a boat.Not just is the height of your very own antenna important, however the height of the receiving antenna also plays its component.

Diagram depicting the importance of antenna heights.
In the above picture, the transmitting VHF antenna is blue. Its signals propagate in a directly line amethod from the antenna, limited by the curvature of the earth.
The green antenna is tall enough to receive the signal. The height of the green antenna can “see” the optimal of the blue antenna.Conversely, the shorter red antenna cannot “see” the blue antenna so they cannot interact with each various other. Even though it is closer to the blue transmitter than the green antenna is, its lower elevation implies it has much less variety.

Calculating VHF selection from antenna height?

We have checked out that the height of the antenna has a straight affect on the feasible range of interaction through VHF radio because it offers line-of-sight communication. 
This suggests that it is feasible to directly calculate the meant range of your VHF based upon the elevation of the antenna and the curvature of the earth.A common formula that you might have actually seen before is

where “d” is the supposed range in nautical miles, and also “h” is the antenna elevation in feet.Pro Tip: My formula will give an extra conservative estimation of the expected array of a VHF radio because of the rounding I have actually done. Underestimating your array is constantly better than overestimating though.
Pro Tip: When I talk about replacing your PLB, tbelow is always the alternative to have the PLB serviced by an authorised agent. The cost distinction vs the astronomical prominence of the PLB indicates that I usually recommend a replacement rather than a business though.Of course, this formula just provides you the range of a solitary antenna. For instance, if you assume a handhosted radio being hosted at sea level, you will certainly probably have actually a elevation of 3 ft. Our formula only provides you a range of around 1.7M.
To get an exact array, but, we have to account for the horizon of the receiving antenna also. You sindicate include the 2 ranges together. Because of this, you deserve to suppose two handhosted VHF radios held approximately 3ft over the water will have the ability to communicate over 3.4M.For a handhosted radio communicating via a large ship’s antenna, we get

assuming the handheld radio is 3ft (1m) above the water and the ship’s antenna is 100ft (30m) over the water.

What is the best height of a VHF antenna?

In a suitable instance, a VHF antenna will be installed as high as feasible. Common locations encompass the optimal of a mast, or on the roof of a cabin.Using the equations we have actually currently discussed, we can watch that the height of your VHF antenna has a direct affect on the array of transmission.On a typical 20ft boat, through an 18ft mast, you can suppose to add about 5 miles to your transmission by mounting the antenna at the optimal of the mast compared to mounting it on the cabin optimal.
Not only perform you advantage from the boosted variety, but the added distance in between the antenna and also other electronic sources on board will reduce the opportunity of interference through your VHF transmission.I have actually written around ways to minimise interference via VHF interactions in this write-up (How To Reduce Interference On A Maritime VHF Radio) if you would like to find out even more about resources of interference from within your own watercraft.

Is antenna height more crucial than power as soon as determining VHF range?

It could seem a tiny counter-intuitive that antenna elevation is the the majority of crucial consideration for determining the array of your VHF interaction. 
Logically, you would certainly think that the power of your transmission is even more important. After all, tright here is a switch on your radio that switches it in between “high power” and also “low power” mode.As it happens, however, antenna elevation is far even more substantial than the power of your transmission once determining selection.The factor for this is that even a low powered VHF transmission has the potential to lug a long distance.
For example, the VHF transmitter brought in the suit of the Apollo astronauts was around 0.5W and might be detected by antennas on earth as soon as the astronaut was on the moon.Reference: Apollo Operations Handbook The low power mode of a marine VHF is around 1W, so will have no trouble transmitting throughout the typical variety of 20 nautical miles or so that you would mean between two yachts.
The line of sight between the two antennas is the many essential consideration once determining the variety of a VHF transmission.

Why have the right to VHF only connect through line-of-sight?

VHF radio interaction takes place about the 150 MHz frequency within the electromagnetic spectrum.Due to its frequency, VHF transmissions tfinish to take a trip in straight lines, without refractivity of the signal emerging.
As the frequency reduces, the radio waves get the capability to refract even more. As you obtain dvery own below 3 MHz, they can refract a lot better.This is why HF communications can take place over a much much longer array than VHF. The finest understand HF frequency, 2182 kHz, drops listed below the instrumental 3 MHz that we figured out as having actually the capacity to refract.
This means that it propagateways as a ground wave instead of ssuggest utilizing line-of-sight. Basically, HF transmissions deserve to bounce off different layers within the setting, giving them the capability to take a trip roughly the earth.VHF signals, through a greater frequency than HF signals, can just take a trip in directly lines.The only method to transmit a VHF signal further is to increase the elevation of your own antenna (the transmitter) and the various other vessel’s antenna (the receiver).
You have the right to always obtain ameans via mounting your VHF antenna low down, but you will sacrifice selection by doing so.

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