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2.4 ghz and interference from Spark ignition

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2.4 ghz and interference from Spark ignition

Old 12-29-2007, 01:50 PM
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Default 2.4 ghz and interference from Spark ignition

I am setting up a GP Yak with a gas engine and controlling it with a 2.4 ghz system. My understanding is that 2.4 is immune to interference from ignitions systems. However, due to CoG limitations, I've mounted my throttle servo immediately behind the engine. A friend recommends that I move it. He says that even though the 2.4 is immune, the servo itself can suffer interference. Is that correct and should I move the servo ?

It's not that hard to move the servo. But now I'm pondering the technicalities of this problem. I have a scant understanding of radios and electronics but thinking about it, doesn't this apply -

Ignition systems create radio waves which can span 72 mhz and other frequency bands (29, 36 etc). These spurious signals can be interpreted by a receiver which can result in incorrect signals being sent to the servo resulting in all sorts of unpredictable behaviour at the servo arm. But at 2.4 ghz, my receiver is well above the spurious ignition generated frequencies (I'm told). So I'm safe at that end.

The servo is not a radio receiver, isn't it just a switching mechanism turning on and off the servo motor according to comands sent by the receiver ? It cannot interprete radio waves itself be they legitimate or spurious. As such, if my receiver is immune and my servo can't receive radio waves themselves, why is it a problem to have it near an ignition source ? Can the spurious radio signals affect other electronics in the servo and/or its motor function ?

Thanks,
Wayne from OZ
Old 12-29-2007, 02:43 PM
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Default RE: 2.4 ghz and interference from Spark ignition

Tontocan
Something for any one to try. Hook your battey to you servo and put a wire on the signal wire and then try your interferince problem and watch what happens. You will not get intererence all the time but different signals will cause problems on a servo not connected to a reciever.
Old 12-30-2007, 04:32 AM
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Default RE: 2.4 ghz and interference from Spark ignition

Okay, I'll take your word for it at the moment but I might try that in the future. If interference can be generated sans receiver, then 2.4 is not going to protect me completely. Thanks for that, servo has been moved.

Wayne from OZ.
Old 06-11-2016, 06:40 PM
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I've seen problems with all systems (Spektrum the worst) and successes but the only receiver that has shown no issues so far is cheap Futaba 4 Channel FHSS (not Fasst)
https://www.youtube.com/watch?v=eh21Vkha6nI
Old 06-11-2016, 09:16 PM
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Ignition interference through the 2.4 ghz antenna is less likely over 72 mhz or the others, but the interference received through servos, servo wires or batteries is the same as 72mhz. There are always improvements to the receivers and servos on how they reject stray false signals, but radio always tries to suck anything out hoping it is a signal. You always have to guard against that.
Old 06-12-2016, 12:35 AM
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I have set ups where my throttle servo is setting next to the engine on the engine box and I have had no problems. 2.4 is not interference free, but supposed to be more resistant. I would try it and see what happens. Run it up on the ground and range check it from all angles.
Old 06-12-2016, 08:18 AM
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Okay, time for me to chime in on this one. Being a navy trained avionic tech, I may have some insight others might not have. There are some things anyone dealing with radio systems should know:
1) ANY wire can work as an antenna unless it is shielded. Live Wire's little example is spot on, though crude. Any RF signal can be picked up though the closer the signal source is to 90 degrees to the wire, the stronger it will be. This, in a nutshell, is how transformers actually work.
2) AM and FM receivers are no different than a 2.4 EXCEPT in how they identify a signal. The big difference in the 2.4 signal is it has an encoded ID in it. When you bind a 2.4 receiver to a transmitter, you are programming the receiver to look for that one ID rather than letting it accept any signal coming in. This is what makes the 2.4 less likely to be affected by a stray RF signals but, as noted by RyanNX211, it's still not 100% effective
3) Even a metal push rod or cable can be used to carry an electrical signal. A push rod is no different than a wire other than the fact it is rigid.
4) Any unshielded wire that has a pulsing signal running through it will transmit a magnetic RF signal. This is referred to as an induced magnetic field. Again, this is used every day in transformer design and operation. A common example of this effect is none other than a car's ignition system, most obvious in the distributor equipped Corvette. To explain this, all you have to do is look under the hood. Since GM tended to put the distributor at the back of the engine, the distributor was normally adjacent to the firewall. With a car made of metal, this was not an issue. With the Corvette, it caused all sorts of problems with the radio, mounted just behind the firewall. Since the Corvette's fiberglass firewall is invisible to RF, the firewall didn't stop the magnetic field caused by the 16,000 pulses through the coil and distributor every minute at an engine speed of 2000 RPM. This was picked up by the radio's antenna cable, plugged in to the back of the radio and even closer to the firewall, and fed to the radio, over-riding the radio signal picked up by the antenna. The result was the radio played nothing but static. By covering the distributor, coil and a short length of the ignition wires with a metal shield and grounding it to the engine block, the problem went away.

Last edited by Hydro Junkie; 06-12-2016 at 08:31 AM.
Old 06-12-2016, 10:50 AM
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Originally Posted by RyanNX211
I've seen problems with all systems (Spektrum the worst) and successes but the only receiver that has shown no issues so far is cheap Futaba 4 Channel FHSS (not Fasst)
https://www.youtube.com/watch?v=eh21Vkha6nI
I fly only Futaba but also with some other compatible Rx's (Orange, FrSky) all using FASST. I have never seen any sign of interference or a "glitch" with what I fly. This over a 5-6 year span in 15 different models. Must be lucky?
Old 06-12-2016, 11:13 AM
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Is it lucky or location? In my area, the Puget Sound basin, there is a lot of RF in the air due to all the radio and TV stations, airport towers and ATC sites, just for starters. Last time I was in Kansas, I saw very little, outside of Wichita, that would have a similar level of RF to worry about
Old 06-12-2016, 01:03 PM
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Originally Posted by TFF
Ignition interference through the 2.4 ghz antenna is less likely over 72 mhz or the others, but the interference received through servos, servo wires or batteries is the same as 72mhz.
I'm speaking anecdotally here: Sometimes the easiest fix is to leave everything the same and just swap out the receiver. In fact, I've seen folks take out the 2.4 receiver that flunked the range test and put back the 72mhz or 6 Meter receiver that it replaced. Unfortunately, this means going back to the frequency board
Experience defies theory. FM held some promise but the Futaba AM Attack was favored until FHSS came along.
Old 06-13-2016, 04:53 AM
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Originally Posted by Steve Percifield
I have set ups where my throttle servo is setting next to the engine on the engine box and I have had no problems. 2.4 is not interference free, but supposed to be more resistant. I would try it and see what happens. Run it up on the ground and range check it from all angles.
Me too haven't ever had a issue. I use Spektrum as my radio system.
Mike
Old 06-13-2016, 05:31 AM
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Originally Posted by Steve Percifield
I have set ups where my throttle servo is setting next to the engine on the engine box and I have had no problems. 2.4 is not interference free, but supposed to be more resistant. I would try it and see what happens. Run it up on the ground and range check it from all angles.
The model in the video doesn't have a throttle.
It has a solid state ignition system and the throttle servo is used to operate a switch to turn it off after a 35 sec climb. I've had a similar system but with a built in servo eliminating switch that plugged into the throttle channel. The results were the same.
Old 06-17-2016, 04:57 PM
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I am surprised this has not been sent to the gas forum.

my understanding is " make sure the metal cap for the spark plug is on tight to the spark plug" that is where the problems come from. one person put a small hose clamp on the cap , to help with contact.
I have spent a lot of time on the gas forum and gained a lot of info.
I don't think 2.4 is totally exempt from the problem, it may not be effected as bad as 72 band.

But do go to the gas forum and have a look, lots of good info.

sticks

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