dbcisco

All I am using is the FCC documents for reference. "no more than .4 seconds" for channel hopping and "1 watt maximum" for spread spektrum transmitters.

MikeL

My Feedback: (3)

You seem to have some misinformation there. Spektrum ships 4.8v packs with their sets.

dbspl

The strength of a 1 watt signal at "half the maximum distance" (whatever that is) will be ALOT less than 32 milliwatts.

As Rodney pointed out, the radiated energy decreases with the square of distance. If you double the distance, you decrease the power by a factor of four. So if the signal strength is 100 (I assume milliwatts) at 10 feet, then the strength at 20 feet will be 25 milliwatts, 6.25 milliwatts at 40 feet, and 1.56 milliwatts at 80 feet.

dbcisco

Not talking about loss off signal at all, rather the intereference. At half the maximum range of a 1 watt TX, a 32mw TX right next to the receiver will have the same signal strength... and interfere if on the same frequency. Further out and the 32ms watt TX next to the receiver will have a stronger signal.
Near the maximum range I could probably overide any signal from the 1w RX with a couple milliwatts of from a bluetooth PDA.

But, as has been previously posted, most RC TXes are only 100mw which makes them even more easily "trounced".

The belief that 2.4Ghz is unaffected by RFI/EMI and other 2.4Ghz devices is proven wrong through out all the forums. Better than FM? Yes. Bullet-proof? No.
It is like comparing chainmail to plate armor. The chainmail won't save you from am arrow or spear. Sadly for the plate armor the world is full of guns. Pretending you have Kevlar or Lexan can get you killed.

dbspl

"Not talking about loss off signal at all, rather the intereference. At half the maximum range of a 1 watt TX, a 32mw TX right next to the receiver will have the same signal strength... and interfere if on the same frequency. Further out and the 32ms watt TX next to the receiver will have a stronger signal."



I'm not talking about a loss of signal either. The energy density of a signal decreases as the signal is spread out over a larger distance from the source. The total radiated power remains the same.

32 mW TX right next to the receiver will have far more signal strength than a 1 watt TX at "half it's maximum range". They will not have the same strength. But yes, if they are operating on the same frequency it could result in interference. However, spread spectrum does have the ability to discriminate between two competing signals. but of course, that will only get you so far.

raptureboy

So any way there was this guy who had a problem with glitching and then........ oh I know he had a problem with glitchs and wanted to know how to fix it WOW! This post is too funny! I think he posted the problem just for fun to see how many tecno-crats he could lure in.

dbcisco

The amount of energy at 1/2 the maximum distance will be the square root of the point of origin. The square root of 1000mw (1watt) is 32mw. Do the math. It is no different than a sound amplifier. Send a tone through a 100 watt amp, walk away until you can't hear it, walk back to the midpoint of that distance and it will sound as loud as if it were a 10 watt amp (square root of 100) at your feet. BTDT.

BTW, I thought someone here was doing the twelfth root of two in their head, been a while waiting for that answer. It is roughly 1.06. Anyone who built a PAIA synth knows that.

dbcisco

If all we did on the forums was answer questions and solve problems there wouldn't be a single thread longer than four posts.

cloudancer03

My Feedback: (22)

something unusal is going on with that crude set up.I suspect anything in there would have the same result.you know what?if you want something to be wrong it wont matter what anyone thinks you simply find an issue and hound it to death..ahhh is the person a wife bty any chance??

cfircav8r

My Feedback: (1)

All I know is my old gold sticker Kraft 5 channel still works great with no glitches and a 4.8v battery. Of course it has newish batteries and servos, and I periodically calibrate the system and change batteries. Never been shot down and still love the feel of the gimbals (still the best ever made.) I admit I have never used it with a gas engine. By the way how did that new plug work?

ian51291

3yrs 15 models 2.4g not one problem.

NM2K

My Feedback: (14)

I usually write articles once or twice a year explaining that there are no absolutes in RF electronics. At least there aren't for lay folks. You can't absolutely shield anything in the RF spectrum. Nor can you absolutely guarantee that a signal will make it from one point to another when dealing with very limited antenna gain and power in an noisy RF environment. It has never been so, is not so presently and it never will be guaranteeable.

I remember a time when a lot larger portion of the R/C modelling crowd was educated, at least at a basic level, in the rudimentary aspects of RF electronics. Naturally, the need for that much education to just install and operate an R/C system has faded as technology progressed. That is as it should be. Unfortunately, the need to be extra careful when making decisions about when a model is to be considered airworthy or not, is not as simple as many think. It is good that you reported your incident here, on RCU. It helps keep all of us aware of the fact that we are dealing with some very complicated equipment that requires very intense scrutiny for safe operation. Keep up the good work.


Ed Cregger

nonstoprc

My Feedback: (90)

Fuataba 2.4G actually changes frequency every 2 milliseconds (http://2.4gigahertz.com/faq/faq-fasst-q888.html). A lot faster than the 0.4 sec max.

dbcisco

If 2.4Ghz was so free of interference than channel hopping would be pretty pointless.

JIMF14D

Ithink some of the confusion here is some people are talking about FCC top level specs for 2.4GHZ band and generic 2.4ghz operation and not the specific implementation by each RC manufacturer.

Example....Fcc=1 watt. Hitec=100mw. Futaba=???? etc.

Most of the comments are general theory and seat of the pants opinion. No real test data of each brand is presented.

The only real test so far is the fact most systems seem to work quite well in the field. And some of the work the guy in NZ did even though he is attacked here. But I don't see the guys attacking him hooking up their spectrum analyzers and noise sources and taking data and providing it to RC community.

And like 90% of the field problems and responses that I have seen at my field.............it is almost always..."the radio did it" or the "wind got me" when in fact most of the time it is an install or flying brain fart!

Hitec A9 works great for me.

Jim D

dbcisco

Who ever heard such a thing.
Are you saying that we amateur engineers make more mistakes than a highly respected design and manufacturing companies' engineers ?
Surely you jest!

NM2K

My Feedback: (14)

Jim, if it isn't too much trouble, could you point me toward the NZ gentleman's posts? I don't remember seeing them. TIA


Ed Cregger

JIMF14D

Here is the link to his general site. See reviews and the list. He has run tests on lots of RC radios. The videos on the Hitec Aurora A9 are informative as to how these systems adapt and work. No it is not the Navy Pax River EMI chamber set up but at least he gives you general info.

His recent summary said he felt the Hitec Aurora and one other HK system were best overall. One guy's opinion.

Have fun

http://www.rcmodelreviews.com/reviews.shtml

dbspl

This is simply not correct. A 10 watt amplifier (I assume there's a loudspeaker attached somewhere) has 10 dB less output than a 100 watt amp. If you measure 100 dB SPL, 1 meter away from the source, then the distance where the output will be down 10 dB (90 dB) will be a mere 3 meters from the source. You will most definitely still hear the loudspeaker at twice that distance, or 6 meters away (84 dB).

dbcisco

Sorry for being far to optomistic. Even though you will hear the 100w the 10w will be louder.
Try watching TV with the radio playing (even at a low volume) at the same time and see if anyone complains.

Apparently interference from other 2.4Ghz devices can interfere with a 100mw TX at far closer ranges than I gave them credit for.
I am now pretty sure that a WIFI phone on the side lines could easily(as far as power) cause glitches.

harphunt

So did you put a new plug in loopman?

peace

JIMF14D

Did Isay such things?...........................

Oh yea, did that guy ever get an R plug and fix his plane. Seems like years ago that he asked for help.

Jim D

A story: Yesterday a guy goes to the runway with a small EP Cub. "taking off"....at which point the Cub roars to life and begins to make rapid 360 ground loops on the runway to the laughter of the vulture row guys watching. Pilot says...."***", caputures the spinning monster and goes to the bench. "Oh my radio has reversed the throttle since last night set up". He fixes same and goes to the flight line. "taking off".....at which point Cub goes 20 feet, lifts off, rolls hard left and smashed into the ground from 5 feet up at full throttle. Back to the field bench. "Oh my radio reversed my ailerons".

I guess the 2.4GHZ gremlins were out in full force yesterday!

dbcisco

I hate it when I can't remember which model is which in memory.[]

JIMF14D

Real radios allow you to name your models........very important for us old guys who are lucky we even remember what are doing out here in the open open with that noisy thing buzzing overhead!

NM2K

My Feedback: (14)

When one is discussing various power levels caused by the inverse square law, one must also distinguish between regular db and dba. Not realizing the difference can lead to a lot of red faces down the pike.


Ed Cregger