quote:

ORIGINAL: Jagthack

Guys
I'm just looking for the radio system that has the least amount of problems that I have been facing. I really don't think it's that hard of a question.

quote:

ORIGINAL: zacharyR

control line

quote:

ORIGINAL: Jagthack

We have had a few say 5 crashes at our field in the past 2 years where guys say they lost control of the plane. I can't speak for them but I know what happened to me. I know 99.98% or crashes are caused by human error. That's not to say a radio can't be the fault. So that leads me to look for a new radio.
What else would you do? You have a new plane, a new receiver with a satellite and a fully charged battery that is the exact size the manufacturer recommends. You have range checked the plane and all looks good. You fly about two mins and then while you are flying a pass from right to left down the runway about 50ft high the plane rolls right and dives into the ground at full throttle. As the plane is rolling out you yell I don't have it and hold up the radio while moving the sticks around and the plane continues to dive into the ground. What error could you have made that would cause that plane to crash? Now look back about three months you had another plane do almost the exact same thing but it was going the other direction and rolled out left. You sent the radio back to the manufacturer and they gave it a clean bill of health. What would you do?

How do you have a field analysis done? How much would that cost?

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2.4GHz: Is It All It’s Cracked Up To Be?

            Asubstantial number of unexplained crashes of radio control model airplanes on2.4GHz frequency prompted me to write this article on the so-called“interference free” radio control systems on the 2.4GHz band.

            The electromagnetic wave spectrum is subjectto the immutable laws of physics.

            Thepropagation characteristics of the 2.4GHz wavelength and the environmentaleffects of this frequency are more complex than on the 72MHz band.  To better understand this, we have to look atthe electromagnetic wave spectrum where 72MHz band is in the broadcastingregion and the 2.4GHz band is in the microwave region.  It is easier to see the huge differencebetween 72MHz and 2.4GHz frequencies when we convert 2.4 gigahertz tomegahertz.  Now it is 2400MHz versus72MHz.  When frequency increases,wavelength decreases.  Therefore, the2.4GHz wavelength is shorter and closer to visible light on the electromagneticwave spectrum.  Since visible light isalso an electromagnetic wave, 2.4GHz wavelength behaves more like visible lightand travels in straight lines until it is reflected, deflected, diffracted orabsorbed.  Reflection and diffractionwill create interference.

            Whenparallel rays of light are reflected by a concave mirror, it greatly increasesthe intensity of light at the focal point. A parabolic dish antenna works the same way for a 2.4GHz electromagneticwave.  Since we can not focus a high gaindirectional parabolic dish antenna between our constantly moving model airplaneand our transmitter, we have to use an omnidirectional vertical antenna systemwhich has much lower signal intensity.

Interference

            The FHSS(frequency-hopping-spread-spectrum) and the DSSS(direct-sequence-spread-spectrum) techniques can share the same band.  However, they interfere with each othercausing a degradation of performance. Range decreases as the number of clear channels decreases.  Bandwidth drops each time FHSS encounters ablocked channel on a crowded spectrum.

            The crowdedspectrum on the 2.4GHz band reduces the bandwidth, increases the ever presentbackground noise, increases the adjacent channel leakage ratio, reduces the range, and causesoverlapping.  Overlapping is a direct interference.

            Unlike the72MHz wavelength which penetrates most objects, the 2.4GHz wavelength behavesmore like visible light.  Signalabsorption from objects on a model airplane like the engines, electric motors,batteries, servos, pushrods, landing gears, switches, wires, etc., may causepath interference.

            Signalreflection from objects in the terrain, like fences, walls, buildings, trees,hills, power lines cause line of sight interference.  High speed data transfer reduces thereceiver’s sensitivity on 2.4GHz band. There is a trade-off between speed versus range.

            The signalstrength decreases quadratically as distance increases at constant radiationlevels.  This is called path loss.  When frequency increases, path loss alsoincreases.  This is one of the reasonswhy 72MHz radios have a better range than the 2.4GHz radios.  We can see this clearly when we look at theWireless Range Calculator:

Frequency                   Distance                      Loss

100MHz                      0.2 mile                       62 decibel

                      2400MHz                      0.2 mile                       90 decibel

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These calculations are under non-existing ideal conditions,less Fresnel (pronounced Frehnel) effect.

            When we flyour model airplane on 2.4GHz, the area around us is known as the Fresnelzone.  Since we have to use anomnidirectional antenna system, the electromagnetic waves will scatter and diffractfrom objects and from the terrain around us. When the diffracted wave reaches the receiver antenna, it is slightly lagsbehind the signal which traveled to the receiver antenna in a straight linethat creates interference due to thephase canceling effect.

            The Fresneleffect also deals with the behavior of electromagnetic waves over a watersurface.  As mentioned before, the 2.4GHzradiation behaves more like visible light, so we have to think of reflectionsand shadows.  Flying a 2.4GHz radio controlmodel over a reflective surface like water, snow, ice or wet terrain negativelyaffects the radio link.  Occasionally a3D aerobatic model plunges into water while hovering.  When the rudder is near the water surface,the prop wash creates a chaotic wave pattern which generates a myriad offalse-signals. 

            The Fresneleffect and the described interference on the 2.4GHz band work pretty well.  We successfully tested this at differentlocations.  Unfortunately, the“unbreakable Tx-Rx link” broke when our model was over 0.2 miles away at 45degree angle.  Despite the fact that a 90decibel signal loss over a thousand feet (0.2 miles) is rather significant, weshould have had control at this distance. There are too many factors that can determine the overall range on2.4GHz. 

            2.4GHzreceivers are not immune to ignition and electrical noise as advertised.  Occasional arc from high tension insulatorscould break the bind.

Latency

            Latency isthe time between stimulation and the beginning of response caused bypropagation delays.  There is a huge timedifference in latency claims by different radio manufacturers.  Some latency claims are in milliseconds,others are in microseconds!  This isconfusing since one millisecond is one thousandth of a second and onemicrosecond is one millionth of a second. 

            Velocity ofelectromagnetic waves is 186,283 miles per second.  The velocity of the electric signal throughconductors is nearly at the speed of light. With an adequate power output, our radio signal will travel onemicrosecond which is one millionth of a second to reach our model airplane onethousand feet away.  This applies to allbrands of radios on 72MHz or on 2.4GHz. As we know, nothing travels faster than the electromagnetic waves.  Therefore, I don’t see how latency could beimproved “50 %” over the leading competitors regardless of differentprocessing.

            A sevenmillisecond latency or a fourteen millisecond latency claim is irrelevant sincethe human being, the RC pilot, has a painfully slow 200 millisecond latency andcan not differentiate between seven or fourteen milliseconds.

Conclusion

            At huge events,like Nationals, the 2.4GHz pin-free radio system makes life easier forcompetitors and organizers.  However,there is a huge difference between flying on 2.4GHz band in the beautiful countryside near Muncie where chances are good that there won’t be any

3 of 4

noticeableinterference and flying on 2.4GHz band in the middle of one of the largestconcentration of population and industries in Los Angeles or other urbanareas. 

            2.4GHzradios under harsh conditions work most of the time, however most of the timeis unacceptable.  Illegal signal boosting,ham radio, and rolling hills further aggravate the situation.              2.4GHzwavelength has much higher incurred losses than 72MHz wavelength.  Therefore, when it comes to range, the 100mWRF output on 2.4GHz radio is no match to a 750mW RF output on 72MHz radio.  When out of range, error correction, uniqueGUID code, and the “robust” pseudo-random control sequence will do no good.  In any case, we should hold on to our assigned frequencies on 27MHz, 50MHz,and 72MHz bands.

            Despiteglowing reviews, the so-called “bulletproof 2.4GHz technology” has range andreliability problems since day one.  Abench test inside a building in a controlled environment where the receiver isa few inches away from the transmitter is meaningless.

            2.4GHzwavelength is not the best choice to control model airplanes.  Furthermore, we have ended up with complexradio systems on an overcrowded band on the electromagnetic wave spectrum.

            The bottomline is that glitch-free software, error-free computers, and aninterference-free radio link is only an illusion.

Dave Horvath

                                                                                                                                    11-11-11

References:

www.google.com

electromagnetic spectrum

Images for electromagnetic spectrum

Videos for electromagnetic spectrum

www.google.com

Frequency-hopping spread spectrum

DSSS and FHSS-Spread Spectrum tutorials

www.google.com

2.4 GHz interference

Interference in the 2.4GHz ISM Band:

Challenges and Solutions by N Golmie

20 Myths of Wi-Fi Interference (RF Solutions)

4 of 4

www.google.com

path loss in the 2.4GHz

Speed vs. Distance ISA

900 MHz versus 2.4GHz – Learning Center

www.google.com

fresnel zone

Images for fresnel zone

ZyTrax-Fresnel Zones and their Effect

www.google.com

diffraction

Images for diffraction

Diffraction-Wikipedia

www.google.com

polarization of light

Images for polarization of light

Videos for polarization of light

MIT Physics Demo-Microwave Polarization

www.google.com

2.4GHz spread spectrum problems

2.4GHz Spread Spectrum problems

www.radiolabs.com

Wireless Range Calculator

Free Space Loss

quote:

ORIGINAL: rgburrill
Going out a few miles FPV illegal, dangerous and stupid.  Thanks for jeopordizing our hobby for the rest of us.

quote:

ORIGINAL: Jagthack

Guys
I'm just looking for the radio system that has the least amount of problems that I have been facing. I really don't think it's that hard of a question.

quote:

ORIGINAL: 1320Fastback

There are such radios.
They are called 72Mhz.

quote:

ORIGINAL: TimBle

quote:

ORIGINAL: Jagthack

We have had a few say 5 crashes at our field in the past 2 years where guys say they lost control of the plane. I can't speak for them but I know what happened to me. I know 99.98% or crashes are caused by human error. That's not to say a radio can't be the fault. So that leads me to look for a new radio.
What else would you do? You have a new plane, a new receiver with a satellite and a fully charged battery that is the exact size the manufacturer recommends. You have range checked the plane and all looks good. You fly about two mins and then while you are flying a pass from right to left down the runway about 50ft high the plane rolls right and dives into the ground at full throttle. As the plane is rolling out you yell I don't have it and hold up the radio while moving the sticks around and the plane continues to dive into the ground. What error could you have made that would cause that plane to crash? Now look back about three months you had another plane do almost the exact same thing but it was going the other direction and rolled out left. You sent the radio back to the manufacturer and they gave it a clean bill of health. What would you do?

How do you have a field analysis done? How much would that cost?

I feel your  pain and completely understand where you are coming from. I've wached quite a few planes go in due to loss of control. In all cases the pilots were expereinced chaps and the symptoms are the same. good battery, range check ok, and theres control during take off and even for a few minutes then nothing.
Watched a mate throw a Nine eagles Skyclimber off the slope last thursday. Everything worked till it was gently flung off the slope. Suddenly no control. We retreived it, dusted it off and flew it again for an hour, not problems.

I think some of the 2.4 radios simply have compromised software with less than adeqaute error checking and correction. The rx ''hangs'' and does not reboot properly, just like some computers do.