I have a doubt regarding the antennas. what decides the range of an antenna?is it the db or the input power. should the antenna signal be amplified before giving the signal to it. is the input signal power deciding the range. please clarify.
what antenna should i use for maximum range.(15-20kms) with video
Replies
I think you have good understanding if this except for the last part. The gain of an antenna is the same weather transmitting or receiving. Data sheets on antennas have only one gain pattern, no Tx or Rx. Gain is gain.
You can only increase the power so much before you run into problems with licensing. Operating high power transmitters requires a license in most countries.
That leaves you with the only real option if operating a lower power transmitter paired with a higher gain antenna.
The higher the gain on the antenna the greater the distance you can transmit / receive but the more precisely you need to point the antenna at the plane.
To get the distances you want you may need to look at some kind of automatic tracking antenna.
To answer second question:
Generally the antenna signal is amplified by the transmitter, and you don't have to mess around with it. But there are some cases where you need to do so.
Be warned though, the addition of an outside amplifier will add more noise to your signal
To answer third question:
If this is for a drone application, generally you'd want a non-directional antenna. Highly directional antennas (those with dB's in the tens and beyond) shouldn't be used on a drone unless you had a specific subsystem to keep the antenna pointed at your reciever.
Always get the antenna that handles the freqeuency band (or range) of your radio, otherwise it won't work very well.
I normally don't jump into forums so quickly like this, but I just couldn't pass this up.
The range of an antenna is determined by two things: input power and gain. Since radio waves can't be seen by the eye, we'll have to do as many analogies as needed...
Input Power:
Think of a calm pool of water. when you drop a small rock in the pool, it will send waves out to all edges of the pool, with the biggest waves right near where the rock fell in. If you dropped a bigger rock, the waves will be bigger and will large for a longer time (and thus a longer distance) than with the smaller rock. Yes, input power affects the range of a signal. The signal itself actually travels in all directions throughout the media (water, air, space, etc.) until it hits a denser media (rock, dirt, trees, people, etc.), at that point, the signal then bounces off of it and/or is absorbed by the denser media in another energy form.
Gain (dB):
Gain is the quality of an antenna to [u]directionalize[/u] the signal. This means that it focuses the radio signal energy into a beam, which distributes the power emitted by the antenna within a narrow cone. Gain can be thought of as the zoom quality of an antenna. As with scopes and binoculars, the higher the zoom, the farther you can see, but the less field of veiw you have.
I don't have enough experiance in antenna design to give the complete scoop on pairing the correct gain for a 2-way transciver setup, but I believe the gain of the antenna has more importantance on the transmitter's part than with a reciever. Simply put, if your antenna has a low gain on your drone, it can still recieve a control signal from your TX, but it can't send a clear enough signal back.
Frequency:
Yes, frequency also has a part in distance, but this is largely due to the media that it goes through. Ultra-High Frequencies (GHz range) tend to have a very low range because they are absorbed and reflected by anything larger than their wavelength.
Consequently, High-Frequencies (3-30MHz range) and all lower frequencies tend to have better long-distance capabilities, simply because they have a much larger wavelength that can pass through or around more stuff.