Dont fly around transmitters. My first crash
- Thread starter Dovivan
- Start date
I've had an issue with a tower myself. I was on a flight at about 350ish ft. I moved out well over the tree line when after about 30 seconds I lost signal and RTH was initiated. After reviewing the video, I lost signal directly over top of a cell tower. Signal returned within seconds of leaving the area above the tower. It ended up being one of those lower cell towers that I couldn't see from the highway or over the tree line of the property.
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Weird thing is that flying that close to microwave towers can cause big problems, yet people fly close to ships, and their radars, and they spew a fair bit of radiation, and not many ppl have problems with it.
ianwood
Taco Wrangler
There's no microwave drums on your microwave tower. Those are sectoral antennas. Probably cellular. Totally different than the power being put out by the OP's tower. If you were to find a focused beam microwave (looks like a kettle drum) and park in front of it, you'd literally cook the Phantom. It could probably withstand the first 30 seconds before damage is done but the IMU would likely misbehave well before then.
Cell towers are mostly short range and not high power. A regional cell might have a little extra juice but it won't be anything like the power coming out of the OP's antenna or when you pass into the beam of a microwave.
N017RW
Premium Pilot
Yea... I'm still a bit skeptical that the tower itself caused this failure. As others have mentioned, potentially sitting right in front of a directional antenna for an extended period of time might cause a failure, but unfortunately "the laws of physics be a harsh mistress" (Futurama). Inverse square law. Those 1-3 kW are at the antenna itself and drop as function of distance^2 as you move away. In addition, it's non-ionizing rf, and it really shouldn't interact with the Phantom at all. Hell, only reason why humans even care about Rf energy is it has a habit of heating up our water molecules (aka, SAR). Otherwise, it is impossible for humans to feel/observe rf. Don't see why the Phantom would be any different.
While I've never flown as close to a tower as the OP, I do live very near the "Needham Antenna Farm" outside Boston. I'm within a few thousand meters of a variety of high powered TV transmitters, and have no issues whatsoever. In fact, it's a great place to fly, as recreational aircraft (other than helos) totally avoid the area. Something about very hard to see guy wires and thousand foot tall antenna towers. ;-)
Any chance of getting a look at those logs? Especially bird-side, not just controller-side. Would love to see what secrets they hold...
While I've never flown as close to a tower as the OP, I do live very near the "Needham Antenna Farm" outside Boston. I'm within a few thousand meters of a variety of high powered TV transmitters, and have no issues whatsoever. In fact, it's a great place to fly, as recreational aircraft (other than helos) totally avoid the area. Something about very hard to see guy wires and thousand foot tall antenna towers. ;-)
Any chance of getting a look at those logs? Especially bird-side, not just controller-side. Would love to see what secrets they hold...
Yeah, well, I still wouldn't stick a controller between my legs.
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If you know what I'm sayin'
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Cluster of testicular cancer in police officers exposed to hand-held radar. - PubMed - NCBI
The inverse square law only applies for omnidirectional radiation - the rate of decrease of RF amplitude is much lower than that for highly directional antennas. Probably why your flights in the vicinity of TV transmitters work OK - the field strength drops off rapidly.
That it is non-ionizing does not help at all - it is the large voltages induced by coupling of the RF field into any unshielded conductors that is the problem, not direct ionization effects.
I don't quite follow how the inverse square law doesn't apply. How could it not apply? Does the law of gravity also not apply in certain situations?
I'm not trying to be sarcastic - I just don't understand what you're saying.
Let's say you're shooting RF like a laser beam, and the RF signal as it moves through the atmosphere is so intense and tight it doesn't spread. In that case I would imagine the inverse square law wouldn't apply. But any other case, the beam spreads, and since the beam spreads, its strength dilutes. And its rate of dilution can be measured by the inverse square law.
Do you disagree?
N017RW
Premium Pilot
It's only valid for 'perfect' isotropic radiation sources (which don't exist).
There is dilution in your laser example but not at the rate described as inverse square.
If you Google it you'll find lots of info as well as graphics which may help you understand.
Here is an excerpt from Wiki that ties to your Laser example:
When you are far from the origin and still have a strong signal, like with a laser, you have to travel very far to double the radius and reduce the signal. This means you have a stronger signal or have antenna gain in the direction of the narrow beam relative to a wide beam in all directions of an isotropic antenna.
There is dilution in your laser example but not at the rate described as inverse square.
If you Google it you'll find lots of info as well as graphics which may help you understand.
Here is an excerpt from Wiki that ties to your Laser example:
When you are far from the origin and still have a strong signal, like with a laser, you have to travel very far to double the radius and reduce the signal. This means you have a stronger signal or have antenna gain in the direction of the narrow beam relative to a wide beam in all directions of an isotropic antenna.
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Radiation sources aside, wouldn't it be prudent to keep one of these around?
Yes - as mentioned above by N017RW, the inverse square law only applies to radiation from ideal point sources. Directional antennas do not behave as point sources or, more specifically, their emitted radiation behaves (as for lasers) as if it came from a point source located a large distance, r₀, behind the antenna, and then attenuates with distance, r, as r₀²/(r + r₀)² - a function that decreases much more slowly than normal inverse square.
I know there no concrete answer and it depends on the transmitter. How close is too close and what is a good safe distance. Back with my phantom 1 I went up towards a tower and probably 500 feet away it went into lost comm mode and thankfully came back. Anyone have any theories on a safe distance? 500 feet, half a mile, even more? It sucks because half the places I want to film usually have antennas on them since they are up high on hills!
Unfortunately it is going to be strongly dependent on the frequency power spectrum and radiator characteristics, and so there really is no simple answer. I would expect a highly collimated microwave horn may be the worst case, but even then the frequency and power will be significant variables. I often run a check with a spectrum analyzer if I suspect strong interference, but even that won't tell you anything about the power in a collimated beam up in the air.
Best estimate - stay away from anything with horns. Cell towers should be mostly OK unless you get really close. Transmission towers (TV and radio) can put out very high radiated power, but it falls off fast with distance.
It's alright for some, I am only allowed 400 here in uk.
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