2.4 gig over water

[Gaza07]

Iam in england and been using the 2.4g spektrum equipment with no problems at all for some time,
I recently attended a waterplane event and was banned from flying because i was on 2.4g and was told there is a known problem with water and 2.4g,
Anyone know exactly what these facts are ?
Or any experiance with 2.4g and water events

[dutch_anykey]

My 0,02 cents....

I worked with long distance MicroWave radio equipment for GSM transmission use. The only thing about those higher frequencies is that the radiation is being "absorbed" by trees and bushes..specially when they are very moist like after some rain. Does not really apply to RC application because you allways want a clear line of sight to your boat plane or heli...
Also wifi is ver sensitive for this. With those long radio point to point transmissions we had special diversity setups because of the tide changes. The water level is really influensing the "straith" line to the other dish receiver. But this is when using an antenna (dish) that produces a focussed beam.
As for RC applications...i doubt that it will be a problem really...
Only thing i can think of would be reflections.... we had some problems with that in the GSM network. So the reflection of the "main' signal is in exact opposit phase and eleminates the signal itself at the RX antenna. But then again the ar7000 receiver from spektrum has 2 units (two receivers) to avoid such thing.

I guess the fact that 2,4 GHz is new in RC is also a big issue. I Recently joined a local flying club here. When they asked what freq. and channel i was using i explained that i didnt have a channel number. I had some explaining to do....while looking at a few pairs of frowning eyebrows. :lol: Luckally they where open for this and accepted it right away

Maurice

[Big Fil]

Flew my Trex with Spektrum radio over the water this weekend without any problems. I think alot of old timers are scrared of the new technology. Part of me understands this because they are used to dealing with what they've had for years, but another part of me feels like they are part of a deer blinded by the light and about to get run over by the technolgy train.

[rototiller]

but another part of me feels like they are part of a deer blinded by the light and about to get run over by the technolgy train.

LOL, nicely put.

dk

[Gary Hoorn]

but another part of me feels like they are part of a deer blinded by the light and about to get run over by the technolgy train.
I have the same problem in my club with SS and electrics. My electrics are called "toys" by the "old and set in their ways" members...
Gary

[Raydee]

I run RC boats with Spectrum in them and LOTS of guys say its bad but I never ever had a single glitch.

[jeffk]

I very seriously doubt that there's any science to back up this myth. Knowing a bit about RF, there's no reason why flying OVER water would have any effect on your heli at all. The water contained within vegetation will absorb RF at 2.4GHZ but this will only affect you if there's a significant amount of plant matter blocking line of sight to your heli. If that was the case, you wouldn't be able to see it to fly it anyway.

Simple fact is that if you are in range and you have line of sight to your heli, you should have complete control of it. RF waves travel in a straight line (for the most part), and nothing that's not in between the transmitter antenna and the receiver antenna will affect the RF energy moving between them.

The only other reason I'd see that you'd get any signal attenuation from a pond would be if you are standing on the bottom under the water and transmitting THROUGH the water.

The old farts are probably just scared of the technology because it's new.

[Raydee]

Some say that the reflection off the water is the problem. The boat guys that have had problems were saying that standing parallel to the water caused problems but moving up away from the water 10 feet or so solved that. Again I have never had a problem even standing IN the water.

[jeffk]

They might believe so, but that's really rather unlikely. Delay of this kind is known as MULTI-PATH, in reference to the time delay between when a direct line-of-sight (LOS) wave reaches a point and when a reflected wave reaches the same point. I would imagine that in order for a multi-path signal to affect a frequency-hopping or spread spectrum system, the difference between arrival of the wave fronts would have to be greater than the frequency-change period. Radio waves travel at the speed of light. Ignoring the atmosphere for a moment, let's say that's 297,000 KM/sec. Doing the math, that's about 30cm in one NANOsecond.

Let's say you're at 20 feet above the water (6 meters). Doing the math, we find that the reflected signals would reach the heli approximately 600 nanoseconds after the direct wave. According to Spektrum, their system spends a few MILLIseconds on each frequency before hopping to the next. So as far as the receiver is concerned, the signals arrive instantaneously. Also, keep in mind that the reflected signal will be weaker than the direct signal and the receiver should be able to lock onto the stronger of the two and reject the weaker.

Besides, signals bounce off of other surfaces (concrete, metal) at 2.4GHz also. Nobody's worrying about that, are they?

Then there's the fact that if the receiver and transmitter's frequency-hopping is synchronized, which they must be for the system to work, then signal delay is irrelevant. Let's say that a particular command pulse reaches the heli via direct wave. Now, in the 600 nanoseconds before the reflected wave gets there, the receiver and the transmitter hop to a different frequency. When the reflected pulse gets to the receiver, the receiver will not pick it up because it's already listening on the new frequency.

There are just so many ways to debunk this.

[gotak]

Spektrum doesn't actually do that frequency hopping. Futaba's 2.4 does. Spektrum uses DSSS for it's "spread spectrum". Just thought I'll point that out.

[jeffk]

Ah, I stand corrected, I had them confused. Water still won't really have any effect on either method though. Check out this site for an explanation of the DSSS system, paying specific attention to the section labeled: "Resistance to Fading (Multipath Effects)"

http://www.maxim-ic.com/appnotes.cfm/appnote_number/1890

So with DSSS, not only does the receiving station reject the reflected signal, it can be set up to make use of it to enhance reception.

Even still, the extremely short distance (by radio communication standards) between your transmitter and the aircraft makes any other argument purely academic. You'd stand more chance of interference from nearby cell or paging transmitters mixing with each other and coming out with harmonics. The FHSS and DSSS systems are designed to minimize these more than the old school PCM and PPM systems anyway.

[flypilot]

Beeing flying Dx7 in waterplanes for some time...no problems whatsoever..