How do antennas work

[Webcruise]

Great video

Cheers
Alexander
Munich

 

[ZX14-R]

Interesting Video...

Thought you would have mentioned having the Antenna on the controller Vertical instead of horizontal.

Cheers

 

[WithTheBirds]

Keep the antennas vertical and facing the Mavic.... that pretty much all there is to it.

 

[hiflyer201]

Great video

Cheers
Alexander
Munich

hey...a zillion likes! I have a question...I know VHF is line of sight and the higher you are the longer the signal lasts. What I'm wondering with drones is..does the higher altitude introduce more interference..enough to overcome the higher altitude. It seems that it does. Is there a happy medium under 400 feet?
thanks

 

[WithTheBirds]

hey...a zillion likes! I have a question...I know VHF is line of sight and the higher you are the longer the signal lasts. What I'm wondering with drones is..does the higher altitude introduce more interference..enough to overcome the higher altitude. It seems that it does. Is there a happy medium under 400 feet?
thanks

No.

Why would you expect more interference at higher altitude? You will probably get increased SNR as any sources of interference on the ground will be further away.

You need to be high enough to maintain a direct signal path to the drone without any obstructions and the flat part of the controller antennas needs to be pointing at it. Its that simple. Not enough detail to make a youtube video on it.

 

[Thomas B]

Keep the antennas vertical and facing the Mavic.... that pretty much all there is to it.

Unless hovering relatively straight up from controller then put the antennae horizontal... regardless of method horizontal( flat face) toward drone.

 

[WithTheBirds]

Unless hovering relatively straight up from controller then put the antennae horizontal... regardless of method horizontal( flat face) toward drone.

Yes- absolutely. You won’t gain as much advantage as might be expected though. While laying the antennas flat on the controller (with the drone directly overhead) does place the drone within the radiation pattern it is also obvious the polarisation is also changed to be 90deg out of phase, the worst possible misalignment.

I don’t have connection issues on the rare occasion I am directly overhead without fiddling the the controller antennas. I have have issues flying down range when I forgot or move them back to vertical though.

 

[LeRoytheBoy]

Great listening and watching.
Not as many times here someone is as thorough and gives detailed info as does Web cruise.
Congratulations on a great informative and educational video.

 

[Fadly]

I found a video where a guy have troubled connection with the drone when the antennas is 90 degrees vertical, but then he flipped it to 45 degrees and suddenly the signal improve.

 

[hiflyer201]

No.

Why would you expect more interference at higher altitude? You will probably get increased SNR as any sources of interference on the ground will be further away.

You need to be high enough to maintain a direct signal path to the drone without any obstructions and the flat part of the controller antennas needs to be pointing at it. Its that simple. Not enough detail to make a youtube video on it.

up to a point VHF navigation works that way but only up to a point. It is line of sight. but there is a lot of traffic on it. It would seem to me WIFI would be the same. Here in Southern California the control tower KWJF had to change tower freqs because of interference from high altitude jet traffic in Mexico.Jet Traffic talking to Mazatlan center..as you know, there are 720 channels or freqs and for comm. and less for Nav..they are getting a little crowded.

 

[WithTheBirds]

up to a point VHF navigation works that way but only up to a point. It is line of sight. but there is a lot of traffic on it. It would seem to me WIFI would be the same. Here in Southern California the control tower KWJF had to change tower freqs because of interference from high altitude jet traffic in Mexico.Jet Traffic talking to Mazatlan center..as you know, there are 720 channels or freqs and for comm. and less for Nav..they are getting a little crowded.

Why are we talking about VHF comms?

Assume the drone won’t be operated above 400ft AGL- the predominant, if not exclusive source, of RF interference will be terrestrial. Probably from wifi, security cameras, baby monitors etc. increased path length between controller and drone will be counteracted by increased SNR gained by increasing distance from sources of potential interference.

 

[Webcruise]

Great listening and watching.
Not as many times here someone is as thorough and gives detailed info as does Web cruise.
Congratulations on a great informative and educational video.

Hello roytheboy,

the video is not from me. I just found it and really liked it and wanted to share with you guys

Cheers
Alexander

 

[Fadly]

Why are we talking about VHF comms?

Assume the drone won’t be operated above 400ft AGL- the predominant, if not exclusive source, of RF interference will be terrestrial. Probably from wifi, security cameras, baby monitors etc. increased path length between controller and drone will be counteracted by increased SNR gained by increasing distance from sources of potential interference.

I found that the wifi environment is very crowded at drone altitude. Up there, with no buildings and trees to block it, wifi signals can go quite a distance. Plus there's harmonic from the power lines and phone lines and even the metal wires people use to hang their laundry.

 

[WithTheBirds]

I found that the wifi environment is very crowded at drone altitude. Up there, with no buildings and trees to block it, wifi signals can go quite a distance. Plus there's harmonic from the power lines and phone lines and even the metal wires people use to hang their laundry.

How did you find that?

 

[Fadly]

How did you find that?

I have wifi analyzer on my phone. There's an open air restaurant on the roof of the tall building about 600 meters from my office building. Up there, the analyzer reading is very crowded, even more so then when i was on the ground level.

 

[WithTheBirds]

I have wifi analyzer on my phone. There's an open air restaurant on the roof of the tall building about 600 meters from my office building. Up there, the analyzer reading is very crowded, even more so then when i was on the ground level.
View attachment 87766

Think about 100ft vs 400ft above ground for the drone and actual LOS distance to any of the active Wifi sources. The number won’t change significantly however the signal will be greatly reduced at the higher altitude.

I was more interested in your claim with respect to clothes line wires. The contribution, to the extent it might exist would be significantly low in solitude to be considered irrelevant. Power lines probably aren’t worthy of consideration either.

 

[DanMan32]

Note that 2.4Ghz and 5.8Ghz are neither VHF or UHF. High UHF ends at 952Mhz.

What is the difference between UHF and VHF frequencies?

Frequency Bands for Wireless Microphone SystemsEvery wireless microphone system transmits and receives on a specific radio frequency, called the opera ...

www.shure.com

 

[DrRobin]

Just to explode some myths:
- VHF is 30 - 300MHz, UHF is 300 - 3000MHz.
- Mavic's run at 2450 or 5100MHz, the operate in the WiFi bands, so whilst one band is technically UHF it is usually refered to microwave or WiFi now.

- When you gain a lot of height you get a really good signal path to lots of noise sources (WiFi, baby monitors, CCTV, microwave ovens, other drones and video senders), the increased distance doesn't over-come the really good signal path, so generally you get more interference with height.

- Power lines and other HF transmitters (< 30MHz) do not cause any interference at 2.45 or 5GHz no matter how powerful they are, if they did they would be operating outside their licence terms. The do interfere with the compass though.

- Some radars can cause interference, especially at 5GHz, these are typically rainfall radar and operate near airports, another reason to avoid these areas.

- There is a lot less interference in rural areas.

- 2.45GHz has less loss from building ands trees/bushes. 5GHz suffers very badly from trees, but does reflect better from buildings. So if you want long range, use 2.45GHz, if you get the choice.

- Antennas have a polarisation, if the you are crossed-polarised you will get a lot of attenuation. The stub antennas on the controller are a 1/4 wave stub at 2.45GHz and possibly a 3/8 wave at 5GHz. When they are vertical, you get all round coverage (best straight off the side), but little straight off the top, that is why it is worth tilting them when the drone is over-head. I am not sure what the drone antenna is, I would assme some sort of patch antenna with hemispherical coverage. It might be circular polarised to give all round coverage regardless of orientation.

- Antenna reflectors do work if they are designed correctly.

- Using the controller antennas at 45 degrees gives you vertical and horizontal polarisation and better all round coverage at the expense of a slight bit of gain, perhaps only 3 or 4dB.

- To get best range, make sure you choose the best channel with least interference (if available on your model), use 2.45GHz (if available), orientate the controller and antennas to ensure that the drone is straight off the side of the antennas (even more important if using reflectors) and make sure they are vertical.

How do I know all of this, my higher degree was in antenna design at 2.45GHz and I design antennas at these frequencies and deploy comms systems in these bands for work, I have done this for over 35 years, nothing much changes in the basic science.

 

[WithTheBirds]

Just to explode some myths:
- VHF is 30 - 300MHz, UHF is 300 - 3000MHz.
- Mavic's run at 2450 or 5100MHz, the operate in the WiFi bands, so whilst one band is technically UHF it is usually refered to microwave or WiFi now.

- When you gain a lot of height you get a really good signal path to lots of noise sources (WiFi, baby monitors, CCTV, microwave ovens, other drones and video senders), the increased distance doesn't over-come the really good signal path, so generally you get more interference with height.

- Power lines and other HF transmitters (< 30MHz) do not cause any interference at 2.45 or 5GHz no matter how powerful they are, if they did they would be operating outside their licence terms. The do interfere with the compass though.

- Some radars can cause interference, especially at 5GHz, these are typically rainfall radar and operate near airports, another reason to avoid these areas.

- There is a lot less interference in rural areas.

- 2.45GHz has less loss from building ands trees/bushes. 5GHz suffers very badly from trees, but does reflect better from buildings. So if you want long range, use 2.45GHz, if you get the choice.

- Antennas have a polarisation, if the you are crossed-polarised you will get a lot of attenuation. The stub antennas on the controller are a 1/4 wave stub at 2.45GHz and possibly a 3/8 wave at 5GHz. When they are vertical, you get all round coverage (best straight off the side), but little straight off the top, that is why it is worth tilting them when the drone is over-head. I am not sure what the drone antenna is, I would assme some sort of patch antenna with hemispherical coverage. It might be circular polarised to give all round coverage regardless of orientation.

- Antenna reflectors do work if they are designed correctly.

- Using the controller antennas at 45 degrees gives you vertical and horizontal polarisation and better all round coverage at the expense of a slight bit of gain, perhaps only 3 or 4dB.

- To get best range, make sure you choose the best channel with least interference (if available on your model), use 2.45GHz (if available), orientate the controller and antennas to ensure that the drone is straight off the side of the antennas (even more important if using reflectors) and make sure they are vertical.

How do I know all of this, my higher degree was in antenna design at 2.45GHz and I design antennas at these frequencies and deploy comms systems in these bands for work, I have done this for over 35 years, nothing much changes in the basic science.

Given the benefit of your knowledge/experience consider the following example..... The drone is 1000m from the Tx and 100 ft above a number of other devices operating in the 2.4ghz band. You increase altitude to 200ft. Inverse square law predicts the signal strength of the devices below the drone will now be 1/4 magnitude. The path length from the drone to TX hasn’t increased significantly. If you are flying over relatively open terrain it is unlikely any additional RF sources that come into view of the drone RX will be close enough to have a significant effect. Overall SNR at the RX should be improved?

Btw- the magnetron in most microwave ovens is 2.4Ghz, I guess UHF oven didn’t go down well with the marketing departments....

 

[DrRobin]

If you double the distance from 100ft to 200ft then the interferring signal will go down by 6dB. So if there aren't any other noise sources in the area then yes your signal to noise will improve. The chances of there been no other interference except in one spot is unlikely.

However, if you are 1,000m away your free space path loss is 100dB. If the interference souce is only 100ft away it's free space path loss is 70dB.

Assume that the controller signal and interference source are similar powers and antennas, increasing the interference source path loss from 70dB to 76dB isn't going to make much difference, noise is still 24dB higher than signal.

There is usually more noise in the 2.45GHz band, especially near built up areas, so if you are in an area with no trees, like a desert or over water, 5GHz might perform better if there is noise.