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Surprising source of radio interference
I spent a good part of today trying to figure out where I was getting interference from. I'm running a weedwhacker conversion engine in a Seagull Sparrowhawk, 2.4 Spektrum, with the telemetry module monitoring battery voltage and engine temp. When I fired it up, I immediately noticed all the control surfaces jittering badly. I checked all the usual causes....metal to metal, loose sparkplug cap, receiver too close to the engine...all that was good. Then it finally dawned on me. The heat sensor for the telemetry module! It was wrapped around the head of the engine, and the wires ran acrossthe magneto, on it's way to the module. Sure enough, when I disconnected the sensor, the jittering stopped. It makes sense, after thinking about it, the sensor wire was just like an antenna, transfering the interference to the receiver. Any of you guys that are running the Spektrum telemetry system and are getting interference, this may be your trouble, too.
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RE: Surprising source of radio interference
I find your conclusion hard to believe.
First of all, in order for your sensor lead to act as an antenna it must be a precise length. The odds for that to be true, are quite low. Next, for your receiver to process a received signal, the signal must contain the proper code. The odds for that to happen are very very low. Then for the PCM decoder to process the received signal, it must match the PCM code. Again for this to happen the odds are very low. If indeed connecting the sensor to the module causes servo jitter then there must be something drastically wrong with your receiver or your power supply. |
RE: Surprising source of radio interference
Any length of wire will act as an antenna and sitting on the magneto there would be plenty of RF to run down the wire. I have also had glitching due to static buildup discharging through the receiver on a helicopter. There doesn't need to be a "signal" a large voltage spike will make all of the servos move. 2.4 and PCM are not imunue to glitching just more resistant to many sources.
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RE: Surprising source of radio interference
Irb75 is correct. I've seen a similar case where ignition noise was killing a Spectrum 2.4GHz. In this case it was caused by the ignition module, not a magneto.
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RE: Surprising source of radio interference
ORIGINAL: lrb75 Any length of wire will act as an antenna and sitting on the magneto there would be plenty of RF to run down the wire. I have also had glitching due to static buildup discharging through the receiver on a helicopter. There doesn't need to be a ''signal'' a large voltage spike will make all of the servos move. 2.4 and PCM are not imunue to glitching just more resistant to many sources. As far as voltage spikes,yes. If you will notice I said there could be a problem with the power supply. However a good power supply with low internal resistance and adequate connections will filter out any spikes. If it were my system I would be carefully checking all the components. There have been reported cases of interference with 2.4ghz systems. I believe in that case the interference is strong enough to affect the servo pulse directly,bypassing the receiver altogether, or a poor power supply. |
RE: Surprising source of radio interference
If it were a poor power supply, why does it only happen when the engine is running? I'm not trying to be a smart arse, I'm really wondering. I'd like to get it right. I plan to hook the TM1000 back up tomorrow, along with the sensors, and unhook them one at a time to see what happens. I'd appreciate any advice you guys might have. I'm not going to fly it till it is 100% right. Almost forgot, I'm running a voltwatch on the receiver battery, and it shows fully charged.
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RE: Surprising source of radio interference
ORIGINAL: ScottMcM If it were a poor power supply, why does it only happen when the engine is running? I'm not trying to be a smart arse, I'm really wondering. I'd like to get it right. I plan to hook the TM1000 back up tomorrow, along with the sensors, and unhook them one at a time to see what happens. I'd appreciate any advice you guys might have. I'm not going to fly it till it is 100% right. Almost forgot, I'm running a voltwatch on the receiver battery, and it shows fully charged. |
RE: Surprising source of radio interference
Thanks for the help. I plan to get to the bottom of it today.
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RE: Surprising source of radio interference
While maybe not directly pertinent to this problem, an antenna can be any length and need not be a specific length to be effective. Now, the ground plane and ground wires are also a part of any antenna system, without them you will not receive any usable signal. However, for most of out RC stuff, a 1/4 wave is the most efficient but that quarter wave can be at the end of a coax or any wire that is an odd multiple of 1/4 wavelength. By properly base loading, you can get by with an even shorter than 1/4 wavelength but sensitivity will suffer due to loss of capture area. A true analysis of an antenna system is really quite complicated and is effected by a large quantity of physical properties as well as electrical. Unfortunately, the higher frequencies such as 2.4GHz are hard to measure without some pretty expensive equipment and testing procedures can be very critical in getting accurate results. N4MCZ
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RE: Surprising source of radio interference
I have also had the "gitters" with the telemetry module. I ended up re-routing the telemetry module antenna and all is well. This happened in 3 different A/C.
Harry |
RE: Surprising source of radio interference
ORIGINAL: Rodney While maybe not directly pertinent to this problem, an antenna can be any length and need not be a specific length to be effective. Now, the ground plane and ground wires are also a part of any antenna system, without them you will not receive any usable signal. However, for most of out RC stuff, a 1/4 wave is the most efficient but that quarter wave can be at the end of a coax or any wire that is an odd multiple of 1/4 wavelength. By properly base loading, you can get by with an even shorter than 1/4 wavelength but sensitivity will suffer due to loss of capture area. A true analysis of an antenna system is really quite complicated and is effected by a large quantity of physical properties as well as electrical. Unfortunately, the higher frequencies such as 2.4GHz are hard to measure without some pretty expensive equipment and testing procedures can be very critical in getting accurate results. N4MCZ |
RE: Surprising source of radio interference
with 72 MHz your transmitter would still transmit if the antenna was not of the correct length. when you had the antenna collapsed all the way you could still control the model just with a more limited range. so just because the wire in not the right length to transmit on 2.4 GHz doesn't mean that its not. it only has a couple feet to go maybe less from the wire to the Rx antenna.
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RE: Surprising source of radio interference
!f any wire/conductor is in close proximity to a moving magnet, like a weed whip magneto magnet, it may generate a current flow into the conductor. maybe you had a "parasitic generator" :D
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RE: Surprising source of radio interference
Check to see if the sensor lead is shorting out in any way to the engine.
Andy |
RE: Surprising source of radio interference
ORIGINAL: Muddin_Mavric with 72 MHz your transmitter would still transmit if the antenna was not of the correct length. when you had the antenna collapsed all the way you could still control the model just with a more limited range. so just because the wire in not the right length to transmit on 2.4 GHz doesn't mean that its not. it only has a couple feet to go maybe less from the wire to the Rx antenna. A PCM system does not produce glitches.( 2.4GHZ systems use a form of PCM) If the received signal does not possess the proper code it is rejected and the system uses the last good pulse received for that channel. As a result, a PCM system does not output glitches like a PPM system does. It just slows down and becomes unresponsive until the fail safe takes over. Then if you haven't set the fail safe it holds the position from the last good data. We have all been spooked by the action of PPM in an interference environment. Its time to revise our thinking and stop blaming our troubles on the ghost of PPM. Times have changed, unless you haven't advanced out of the PPM muck yet. |
RE: Surprising source of radio interference
Dirtybird this most likely isn't interference on the rf signal. It is an induced voltage in the sensor wire due to the magneto, which is acting like..........an antenna. The voltage is going into the receiver not providing any "signal" it is swamping everything or the voltage spike is overloading some component causing the servos just twitch violently. Nothing to do with PCM code or 2.4. Nothing is imune to this type of interference.
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RE: Surprising source of radio interference
ORIGINAL: lrb75 Dirtybird this most likely isn't interference on the rf signal. It is an induced voltage in the sensor wire due to the magneto, which is acting like..........an antenna. The voltage is going into the receiver not providing any ''signal'' it is swamping everything or the voltage spike is overloading some component causing the servos just twitch violently. Nothing to do with PCM code or 2.4. Nothing is imune to this type of interference. |
RE: Surprising source of radio interference
I had a bad ignition that affected all the surfaces on a 2.4 system. The plane even flipped inverted once. I wrapped the ignition in ferrous metal and grounded it to the crankcase. Probelm solved. Talk all the theory you want, but 2.4 will glitch when swamped. Just takes more RFI to do it.
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RE: Surprising source of radio interference
ORIGINAL: ec121 I had a bad ignition that affected all the surfaces on a 2.4 system. The plane even flipped inverted once. I wrapped the ignition in ferrous metal and grounded it to the crankcase. Probelm solved. Talk all the theory you want, but 2.4 will glitch when swamped. Just takes more RFI to do it. |
RE: Surprising source of radio interference
ORIGINAL: dirtybird Any length of wire will not act as an antenna. It needs to be a multiple of 1/4 wavelength to be an effective antenna. Any length CAN be an antenna, multiples of the 1/4 wave makes it an effective antenna. |
RE: Surprising source of radio interference
2.4 isn't immune to RF noise. A buddy was trying to start a Cub he'd just bought with a Quadra 35 up front. Every time he flipped the prop to start, the controls would go crazy. Happened to notice it said Lawn Mower on the plug. I had a proper resistor plug in my van. Stuck that in and everything was cool. Another guy taxied out his Pitts to take off and as soon as he opened the throttle it went full right rudder and down elev. Had a look at it and the problem was the shielded plug cap was not on tight. Soon as he opened the the throttle, the prop blast pushed the cap away from the plug. Let off on the gas and it would go back to touch the plug. You've probably found these caps need to be snapped on hard as they are a tight fit.
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RE: Surprising source of radio interference
No one has said 2.4 is immune to interference. What I am saying is they don't glitch when interfered with. They simply go to fail safe and stop working.
In your case I would suspect the servos that go wild are not high quality. Strong interference pulses like you get with unshielded ignition noise can be directly coupled to the servo pulse bypassing the receiver altogether. Low cost servos may not have proper bypass circuitry. Another cause could be high internal resistance NIMH batteries for the receiver battery or poor connections. I sure wouldn't fly one of those until I determined the cause. |
RE: Surprising source of radio interference
ORIGINAL: ScottMcM I spent a good part of today trying to figure out where I was getting interference from. I'm running a weedwhacker conversion engine in a Seagull Sparrowhawk, 2.4 Spektrum, with the telemetry module monitoring battery voltage and engine temp. When I fired it up, I immediately noticed all the control surfaces jittering badly. I checked all the usual causes....metal to metal, loose sparkplug cap, receiver too close to the engine...all that was good. Then it finally dawned on me. The heat sensor for the telemetry module! It was wrapped around the head of the engine, and the wires ran acrossthe magneto, on it's way to the module. Sure enough, when I disconnected the sensor, the jittering stopped. It makes sense, after thinking about it, the sensor wire was just like an antenna, transfering the interference to the receiver. Any of you guys that are running the Spektrum telemetry system and are getting interference, this may be your trouble, too. BV |
RE: Surprising source of radio interference
Both planes I mentioned above flew fine prior to and after the problems were solved, with no more glitches, so there were no servo problems.
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RE: Surprising source of radio interference
ORIGINAL: Bill Vargas ORIGINAL: ScottMcM I spent a good part of today trying to figure out where I was getting interference from. I'm running a weedwhacker conversion engine in a Seagull Sparrowhawk, 2.4 Spektrum, with the telemetry module monitoring battery voltage and engine temp. When I fired it up, I immediately noticed all the control surfaces jittering badly. I checked all the usual causes....metal to metal, loose sparkplug cap, receiver too close to the engine...all that was good. Then it finally dawned on me. The heat sensor for the telemetry module! It was wrapped around the head of the engine, and the wires ran acrossthe magneto, on it's way to the module. Sure enough, when I disconnected the sensor, the jittering stopped. It makes sense, after thinking about it, the sensor wire was just like an antenna, transfering the interference to the receiver. Any of you guys that are running the Spektrum telemetry system and are getting interference, this may be your trouble, too. BV |
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