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2.4 - Why Are They Failing?

Old 01-21-2011, 10:06 AM
  #426  
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Default RE: 2.4 - Why Are They Failing?


ORIGINAL: rmh

problems are same as full scale-most problems are operator error- about 99.9%
Amen on that
Old 01-21-2011, 04:59 PM
  #427  
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Default RE: 2.4 - Why Are They Failing?

"Yes MY microwave is operating on a frequency of 2450 Mhz. See posted picture.
To answer your question "what modulation is it?"
I do not think it is modulated. All we have in there is a magnetron tube in an oscillating circuit tuned to this approximate frequency and spending its UHF energy in a cavity which is the area where we place the stuff to be heated. "

Remember oscillation=modulation
Old 01-21-2011, 05:38 PM
  #428  
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Default RE: 2.4 - Why Are They Failing?

HellcatAce,

Please look up the word "modulation" in a good dictionary.

An oscillation of constant amplitude and non-varying frequency or phase is a carrier and does not transmit any intelligence.

It has to be interrupted such as when transmitting Morse code or other codes or it has to be varying in amplitude or in frequency or in phase to carry some intelligence like the commands to our model aircrafts.

The variation is referred to as "modulation".

Note ___I will not pursue the subject.

Zor


Old 01-21-2011, 06:28 PM
  #429  
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Default RE: 2.4 - Why Are They Failing?

psb667

The model of my corona is DSSS.

Thank's!
Old 01-21-2011, 11:23 PM
  #430  
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Default RE: 2.4 - Why Are They Failing?

My walkera radios do some thing very similar. I dont know why. i had always chalked it up to cheap components. They seem to bind solidly once they are bound though.this link is from a earlier post. http://www.rcmodelreviews.com/spreadspectrum01.shtml these will help with the modulation thing. You messure the microwaves modulation with a good one of these.http://en.wikipedia.org/wiki/Oscilloscope http://en.wikipedia.org/wiki/Modulation http://dictionary.reference.com/browse/modulation These a really expensive but one these would help to http://www.google.com/products/catal...d=0CDIQ8wIwAw#
Old 01-21-2011, 11:57 PM
  #431  
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Default RE: 2.4 - Why Are They Failing?

Nitro here is a better link than the one with all the auto parts.http://www.futaba.com/products/irc/technology/index.asp here is another one http://en.futaba.co.jp/industrial/index.html
Old 01-22-2011, 12:41 PM
  #432  
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Default RE: 2.4 - Why Are They Failing?

I only have 2 2.4 GHz radios, one for the Park Zone micros, and one for a Fly Zone Albatross. I would so far say that to date, I have had no more radio problems than with 72 MHz. That's basically since I've done far more flying on 72 than 2.4, so I'm basically estimating failure rates of 30 years flying on 72 vrs about 1 year on 2.4. That's also includes admitting that most "Radio" or "Interference " problems I've had in those 30 years were actually dumb thumbs or ignoring things like obvious low battery warnings, switch failures, things like that. Maybe 4 actual cases of interference, and maybe 8 of actual radio issues. I have had a problem with my PZ Micro P-51 because the "Brick" (said I've been doing this a while) broke free of it's mounting in the plane. That is, the AR6200 is mounted with 2 or 3 dots of some kind of white adhesive to the plane fuse. I repaired this with 4 drops of good ol' Ambroid. But, the last time I was flying the Mustang, the motor just basically turned off, went into a roll, then dived into the scrub. No damage done, and when I checked, everything worked fine, including on a ground check from a greater distance. I've had 8 good flights since.

Nothing man makes is 100% reliable. One my jobs in the lab where I worked was to run RFI testing. We went from about 40 Hz to 10 GHz, field strengths to 300 V/m (much higher than most commercial products need to be tested to). It was not unusual to find a problem, test a couple times in a row, then call the design engineer over and be unable to repeat it in front of him, but as soon as he was gone, have the problem return. Or have a problem one day, and not have it another. RF is almost an art and manipulation of black magic as it is a science.

2.4 is probably more intereference free than 72, but not absolutely.
Old 01-26-2011, 12:46 PM
  #433  
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Default RE: 2.4 - Why Are They Failing?


ORIGINAL: Zor

HellcatAce,

Please look up the word ''modulation'' in a good dictionary.

An oscillation of constant amplitude and non-varying frequency or phase is a carrier and does not transmit any intelligence.

It has to be interrupted such as when transmitting Morse code or other codes or it has to be varying in amplitude or in frequency or in phase to carry some intelligence like the commands to our model aircrafts.

The variation is referred to as ''modulation''.

Note _ _ _ I will not pursue the subject.

Zor
Well thats great, except the fact 2.4 radios operate on a digital carrier. That carrier is not modulated in the analog fashion you correctly desicribed. It is a constant oscillating frequency that carries a digital bit stream. Any oscillator can produce harmonics which can be perceived as modulation by any device which must accept outside interference. Last time I looked at my microwave, it didn't have a sharp tuned mask filter system, which would be required to eliminate any harmonics created by the microwave's oscillator.

So in this case, a microwave oven can indeed cause interference to a 2.4 radio.

Old 01-26-2011, 03:09 PM
  #434  
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Default RE: 2.4 - Why Are They Failing?

In escence, modulation is the modification of the carrier wave in order to transmit information. There are several ways to do this. Sometime, a signal can be victimized by undesired modulation not part of the circuit design or operators intent.

The first radios, like many of the early single channel radios from the 1930s to the late 60s were very simple. The carrier was held OFF until a control was keyed, at which time the carrier was turned ON, and detected at the very simple reciever. Later, the carriers were ON anytime the transmitter was on, and the carrier was Amplitude Modulated by a tone generator activated by pressing the key, with the resulting signal decoded in a more complex reciever. 400 Hertz was a common modulation frequency.

This eventually developed into transmitters with multiple tone generators to enable multiple controls. The reciever would either use tuned filters, or a resonant reed relay system with multiple reed contacts of different lengths, each responding to a given frequency. Early proportional radios used a single modulating frequency, but varied the frequency with which the transmitter was keyed, and later also the proportion of on to off, to get multiple control functions. In the early 50s, the Good brothers, probably among others, tied this in to their TTPW, Two Tone Pulse Width system, which used two different tones, each with a rate/width control, to give up to 5 or 6 controls. Then along came Frequency modulation, in which keying the transmitter either dropped the carrier frequency or raised it a small amount, which provided the control information. More modern proportional gear modulates in a sequence of events with a reference pulse followed by some number of pulses, with the width of the pulses and their position in the pulse string detemining whioh control is being directed. This can be any form of modulation. The latest scheme, which is probably FM, sends out a stream of digital words which contain an identifier for the particular control channel and the position for the servo to go to and hold. You should see what the waveform looks like on a truck's power line communications system. Looks like a combination of AM and FM.

Regardless of format, any modulated carrier will have not only the desired information, but will also pick up harmonics and sub-harmonics from many sources, including but not limited to poor solder joints, tolerance stack in the component, atmospheric conditions, loose battery connections, loose internal connections, Drift in other transmitters physically close to either the prime transmitter or the plane it's controlling, and sometimes even RF reflections from nearby things like power poles and lines, fences, steel building skeleltons and siding, construction equipment. The reciever is not only getting this mess, but can itself be affected by atmospherics, internal component tolerance stack-up, bad connections, as well as things like metal to metal contact in the engine and control linkages, Ignition pulse in spark plug equipped gassies, shadowing and reflection from metal or carbon fiber pushrods, carbon fiber structural members, even larger engines, affecting the antenna. Hey, sometimes, especially at higher frequencies, even something as simple as a lead-mounted transistor or capacitor slightly out of design position, can cause problems.

I once was using a nice $7000 oscilloscope to look at a high frequency signal to try to find a problem. Through most of the circuit board, the signal was nice and clean when a captured signal was subjected to the scope's Fourier Analysis program. Then at one point in the circuit, there were a number of sub harmonic spikes, a couple of which had a higher amplitude than the original signal. Our circuits are usually built with Automotive grade components. In that one part of the circuit, we ended up having to go with Mil-spec parts, in spite of the crying of the bean counters. Problem solved, just throw money at it. Actually, the components cost a whole $.30 more than the original design parts.

Years spent trying to develop circuits that can function safely in heavy RF fields has convinced me that RF design is almost equal parts Engineering Skill and knowledge, Science, Art, Luck, and some Black Magic. Some circuit designers agree completely with this view. The designers will over time improve interferrence resistance, but probably won't totaly eliminate it for another few hundred years. Maybe! 72 MHz was better than 27, 2.4 GHz is apparently better than 72 MHz. Some investigative work was done on 900 MHz with good results. Seems the higher the frequency, the less risk of interference. But, the trickier the physical circuit layout.
Old 01-26-2011, 04:06 PM
  #435  
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Default RE: 2.4 - Why Are They Failing?


50+AirYears,

Congratulations for a very nice posting well writen and formatted.

No words that mutilate the English language.

A very good resume of the RC control development and history.

Zor
Old 01-26-2011, 04:46 PM
  #436  
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Default RE: 2.4 - Why Are They Failing?


ORIGINAL: HellcatAce


ORIGINAL: Zor

HellcatAce,

Please look up the word ''modulation'' in a good dictionary.

An oscillation of constant amplitude and non-varying frequency or phase is a carrier and does not transmit any intelligence.

It has to be interrupted such as when transmitting Morse code or other codes or it has to be varying in amplitude or in frequency or in phase to carry some intelligence like the commands to our model aircrafts.

The variation is referred to as ''modulation''.

Note ___I will not pursue the subject.

Zor
Red inserts by Zor

Well thats great, except the fact 2.4 radios operate on a digital carrier. I never heard (except now) of a "digital carrier". A digitally modulated carrier, yes, but not a digital carrier.That carrier is not modulated in the analog fashion you correctly desicribed. I did not say that a carrier is modulated ONLY by analog fashion. A carrier can be modulated in many ways as I mentioned. It is a constant oscillating frequency that carries a digital bit stream. The constant oscillating frequency is the carrier. The digital bit stream is the modulation. Any oscillator can produce harmonics Yes which can be perceived as modulation Harmonics, if produced,do carry the modulation but not usable. by any device which must accept outside interference. devices that do not reject the harmonics Last time I looked at my microwave, it didn't have a sharp tuned mask filter system, which would be required to eliminate any harmonics created by the microwave's oscillator. If it did not last time you looked, it will not next time you look .
Microwave oven are tuned by a cavity which has a very high Q ( for readers unacquainted, the Q is a measure fo the sharpness of the resonant circuit, a cavity in this casecontrolling the oscillating frequency). Harmonics would be very low level and above 10 Ghz.

So in this case, a microwave oven can indeed cause interference to a 2.4 radio.
Possibly but I made some test with my Spektrum AR7000 and placed the Rx and its satellite at different locations around the microwave and right against it and I did not see any problems interfering with it while the Tx was 30 feet away (my house is not 100 feet long __) and on low range test power level. Every time the system was turned on it bound and servos responded correctly.
Regards to all from Zor.

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