Learn me this on GPS please

[Tbonham27]

If I am correct that with a minimum "satellite" count the aircraft is always online regardless of terrain...and controller to bird connectivity is limited to straight line signal path....why is it not designed to allow or make possible control in obstacle present conditions?
Basically control via satellite? T hanks

 

[gingerbloke]

Don't quite understand the question, but satellites (in our case) are not offering communication link of any sort, just used by the GPS system to give location information. The accuracy of this location depends heavily on satellite count.

 

[Meta4]

If I am correct that with a minimum "satellite" count the aircraft is always online regardless of terrain...and controller to bird connectivity is limited to straight line signal path....why is it not designed to allow or make possible control in obstacle present conditions?
Basically control via satellite?

You might have to ask your question again with other wording so people can understand it.
The Phantom is controlled by radio waves travelling between your controller antennas and the antennas in the legs of your Phantom.
If you want your control to go via a satellite in space, what would that do to the time it would take for control signals to reach your Phantom?
I don't think that would be an advantage.

 

[Kirby Johnson]

TBonham27: In answer to your sort of question, given that it appears you are not super familiar with the nuts and bolts of the signals:

Between you and the GPS satellites you have control of the quadcopter. It knows it's position, except when you tell it to ignore it, in ATTI mode, via the GPS satellites. You locally tell it what to do with respect to it's position gained from the satellites, but the very nature of GPS satellites is one way communication, from them, to your quadcopter and a million others. It is impractical to try to let those million or so quadcopters talk to the satellites. It is like a local radio station. Your radio receives the signal but cannot talk back.

 

[Kwas]

Being that RF travels at only about 200 miles per second less than the speed of light (186,000,200 )miles per second, there would be negligible lag time.

 

[Kirby Johnson]

Being that RF travels at only about 200 miles per second less than the speed of light (186,000,200 )miles per second, there would be negligible lag time.

Yeah I know, but I thought it wouldn't add anything to embarrass someone.

 

[Meta4]

Being that RF travels at only about 200 miles per second less than the speed of light (186,000,200 )miles per second, there would be negligible lag time.

Ever used a satellite phone?

 

[N017RW]

Being that RF travels at only about 200 miles per second less than the speed of light (186,000,200 )miles per second, there would be negligible lag time.

Please cite your source.

Photons carry electromagnetic energy. The difference between light and RF is frequency.

Humans can only see (detect) a very small sliver of the EM spectrum.

 

[N017RW]

Yeah I know, but I thought it wouldn't add anything to embarrass someone.

Can you cite a source for this?

I mean an explanation how some photons travel faster or slower than others.

 

[Kirby Johnson]

Can you cite a source for this?

I mean an explanation how some photons travel faster or slower than others.

I'll make this as simple as practical. In the grand scheme of things in human velocity terms, none of it matters, whether there is any speed difference or not is infinitesimal to a human. As far as we can tell, it is all instantaneous until you start talking about distances like another galaxy away.

 

[sar104]

Can you cite a source for this?

I mean an explanation how some photons travel faster or slower than others.

The velocity of propagation of EM waves in a vacuum is given by c = 1/√(µ₀ε₀) where µ₀ and ε₀ are the permeability and permittivity of free space, and are frequency invariant.

Permeability doesn't vary much in other media, but permittivity increases in dielectric materials, including air. The relative permittivity of air is approximately 1.00059, and is almost frequency independent in the RF to visible range of the spectrum. However - that value of relative permittivity for air does lead to the speed of propagation (visible and RF) being roughly 56 miles per second slower than in a vacuum. Possibly that was the confusion - dispersion is negligible but variation from a vacuum is not.

 

[sar104]

I'll make this as simple as practical. In the grand scheme of things in human velocity terms, none of it matters, whether there is any speed difference or not is infinitesimal to a human. As far as we can tell, it is all instantaneous until you start talking about distances like another galaxy away.

That is clearly not correct. Propagation time from the sun is around 8 minutes. Propagation time from the moon is 1.3 s. Round trip communication time via a geosynchronous satellite is 0.2 s minimum, not counting other latency, which bumps it up considerably. None of those delays is imperceptible.

Low-orbit satellites have lower round trip times in principle, of course, but are virtually useless for this kind of communication due to availability and power requirements.

 

[N017RW]

The statement did not seem to be speed vs the medium but speed vs the frequency.

 

[sar104]

The sratement did not seem to be speed vs the medium but speed vs the frequency.

Agreed - as I mentioned it was implying dispersion in either vacuum or the earth's atmosphere, which does not occur measurably. Hence my comment that it was possibly confusion with the variation by medium. And clearly dispersion is significant in other dielectric media, where ε can be considerably frequency dependent.

 

[Kwas]

Please cite your source.

Photons carry electromagnetic energy. The difference between light and RF is frequency.

Humans can only see (detect) a very small sliver of the EM spectrum.

A simple search will confirm my numbers.

 

[N017RW]

A simple search will confirm my numbers.

No real need to search but to be a good citizen this is what my simple search found:

Actually, radio waves travel very quickly through space. Radio waves are a kind of electromagnetic radiation, and thus they move at the speed of light. The speed of light is a little less than 300,000 km per second. At that speed, a beam of light could go around the Earth at the equator more then 7 times in a second.

Where can I find you source?

 

[sar104]

A simple search will confirm my numbers.

No - actually it won't. See my comments in post #11 above.

 

[Meta4]

Being that RF travels at only about 200 miles per second less than the speed of light (186,000,200 )miles per second, there would be negligible lag time.

If transmission delay to/from satellites really was negligible , there wouldn't be many complaints about latency

A simple search will confirm my numbers.

LMGTFY

 

[umanbean]

Don't GPS receivers on Earth use some kind of time-shift measurement calculation to determine your position?

But I guess that doesn't make any difference in the speed the radio waves are actually traveling

 

[tcope]

Don't GPS receivers on Earth use some kind of time-shift measurement calculation to determine your position?

But I guess that doesn't make any difference in the speed the radio waves are actually traveling

GPS signals need to compensate for things like gravity and the speed of the satellite as these things slow down time. GPS sats are 12,000 miles from the Earth and almost 9000mph. Basically 45,900ns slower each day. This amounts to GPS being off miles.

So as far as GPS is concerned, it is more the effect of speed and gravity on time then the speed of the signal.