Tech question: how does FPV transmit so far over WiFi?

M

MooseMan

Member
Or do I have it wrong?

I'm trying to understand how I'm getting FPV to my phone with my SJRC F11. I connect to my drone's wireless. It flies anywhere from 200-700 meters (depending on where it is) and I'm receiving this video stream. However when it gets out of range, my phone connects to a more local wifi, and I retrieve the quad by hitting the home button on the controller.

So how is this working? My home wifi only goes 100 feet!
 
I think that the WiFi works between your devices and does not depend on another WiFi source like your home WiFi. WiFi is a specific frequency. Range is dependent on the RF power for each device. Cell Phones can piggyback the WiFi signal to it's carrier wave to Cell Towers. Figure about 5 miles range from the cell phone to the Cell Tower. Your Drone is usually LOS and does not transmit to the cell tower. If it did, you could get phenomenal range. This was explained to me by a Communications Engineer. I don't knows if he was just pulling my leg.
 
What he said but would add it depends largely on where the transmitting and receiving antenna are relative to each other as well as orientation and as importantly the stuff between the two.
 
A little puzzled over that too. WIFI barely covered the house, but the spark works WAAAAAYYYY over there. Perhaps it sends a stronger signal than the wifi routers.
 
To illustrate, the WiFi in your house has a limited range set by the device manufacturer, usually around 300 feet. WiFi is another Radio RF Source and is a double superheterodyne transmitter/receiver, like your cellphone is. It produces a transmission along the 802.11 MHz wavelength. Any device can use the WiFi frequency and can handshake with any other device also using the WiFi frequency. You don't have to be near a WiFi Modem for these to communicate with each other. The frequency doesn't drive the amplitude of the signal, the transmitter RF circuit does. You just need a powerful transmitter and sensitive receiver to work in the rhelm desired. The Quad sends a strong WiFi signal, your cellphone in WiFi mode senses that signal. No modem is necessary in between. I am an old time CB Radio Enthusiast and that's the way it worked back in the 1960's and 1970's. It's just more sophisticated these days.
 
WiFI Routers and modems transmit at 100 MW of power. Your cell phone only transmits at 15MW of power. This limits the range of your WiFi capability at home.

The Controller/remote on my Phantom and the Aircraft also transmit at 100 MW of power. (this takes into account antenna gain. But disregard)

So you can see an obvious advantage in power alone for our QUADS. Add the benefits of always being in LOS. haha. And the obvious benefit of altitude. (of the quad). And Voila.

Or maybe I made that up. :cool:

Have fun Yanking and Banking!
 
ArmyVet said:
WiFI Routers and modems transmit at 100 MW of power. Your cell phone only transmits at 15MW of power. This limits the range of your WiFi capability at home.

The Controller/remote on my Phantom and the Aircraft also transmit at 100 MW of power. (this takes into account antenna gain. But disregard)

So you can see an obvious advantage in power alone for our QUADS. Add the benefits of always being in LOS. haha. And the obvious benefit of altitude. (of the quad). And Voila.

Or maybe I made that up. :cool:

Have fun Yanking and Banking!
Click to expand...

Made up with a typo?
 
LoneRCRanger said:
To illustrate, the WiFi in your house has a limited range set by the device manufacturer, usually around 300 feet. WiFi is another Radio RF Source and is a double superheterodyne transmitter/receiver, like your cellphone is. It produces a transmission along the 802.11 MHz wavelength. Any device can use the WiFi frequency and can handshake with any other device also using the WiFi frequency. You don't have to be near a WiFi Modem for these to communicate with each other. The frequency doesn't drive the amplitude of the signal, the transmitter RF circuit does. You just need a powerful transmitter and sensitive receiver to work in the rhelm desired. The Quad sends a strong WiFi signal, your cellphone in WiFi mode senses that signal. No modem is necessary in between. I am an old time CB Radio Enthusiast and that's the way it worked back in the 1960's and 1970's. It's just more sophisticated these days.
Click to expand...
My head is spinning. I can't say that I understand, but I'm interested in trying to extend the range - starting with the idea that the primary antenna limitation is my phone. Maybe I'll look for a 5ghz portable repeater.
 
MooseMan said:
My head is spinning. I can't say that I understand, but I'm interested in trying to extend the range - starting with the idea that the primary antenna limitation is my phone. Maybe I'll look for a 5ghz portable repeater.
Click to expand...
Just get a strong enough 5.8GHz VTX and receiver repeaters won't be worth attempting maybe directional antenna can help but repeater would need to be between phone and quad and how to power it there plus extra latency and hops for any signals (not to mention digitizing and decoding)
 
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