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Signal Interference

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Old 08-02-2006, 04:29 PM
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flyinrain
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Default Signal Interference

I have a GP Patty Wagstaff Extra 300 that I’m having a radio signal problem with. I have a new Futaba radio and FMA Direct FS8 receiver. I’m loosing signal contact with the airplane and can’t find the problem. I’ve tried different Futaba radios and channels with no improvement. I’ve even had every thing calibrated and no improvement. The airplane has a Fuji 50 gas engine with magneto and all radio gear is at least 12 inches away from the engine. No one else at the field has problems like this. The airplane does pass the ground check so I’m out of things to do so please help.
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Old 08-02-2006, 05:01 PM
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Default RE: Signal Interference

flyinrain,

Are you getting glitches, or is the annunciator showing fail-safes after flying? I had, and may still have, the same problem in an Extra with a ZDZ50.

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Old 08-02-2006, 08:51 PM
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Default RE: Signal Interference

It is showing fail safe and I did see a very short loss of control of the airplane in flight.
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Old 08-02-2006, 10:06 PM
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Default RE: Signal Interference

flyinrain,

My ZDZ-powered Edge had the same problem. Unfortunately (and this was my foolishness....was having too much fun) this situation ended in a loss-of-control resulting in quite a bit of damage. Do not fly yours until you correct this!

How far does your radio range check? Is it the same with engine running and not running?

I improved my range-check distance by putting buffers on the elevator servos. They are driven from the same channel with a buffer to which two servos can be connected. Originally, the antenna ran along the bottom of the fuselage, parallel to the elevator servo extensions. Now it goes to the top of the vertical stabilizer, no longer parallel to the extensions.. I have been told by radio people that placing an antenna parallel to long extensions can cause reception problems. I do not know if that is true.

Also, i think long extensions may possibly act as antennae and send spurious signals to the receiver. The elevator extensions were originally connected to a non-buffered "Y". This, in effect, created a total extension (including the leads on the servos) of about 60 inches. That is both sides of the "Y" feeding one channel in the receiver.

I have not flown the plane since modifying the radio installation, but it seems better on the ground. It will now repeatedly range check at 55 to 57 yards with the antenna completely collapsed. This distance meets or exceeds the range-check distance specified by FMA. It is a 9C Tx. which has also been tuned to spot-on frequency. Actually, I have been a little reluctant to put this plane back in the air.

The ZDZ has an electronic ignition and it does not seem to be putting out any RF noise.

I have used FS8s very successfully in four other (glow-powered) airplanes with the same transmitter and at the same field.

Does anyone else have experience with FS8s in gas-powered planes (although I don't think the gas engine had anything to do with my trouble)????
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Old 08-02-2006, 10:42 PM
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Default RE: Signal Interference

Thanks for the reply. Ground range checks out to 50 yards which is what the FMA manual says. It was less then this and I changed the servo wire routing to the tail which helped a little. The antenna on the airplane runs along the bottom. I do have a non-buffered Y and your explanation on it sounds good so I will change it out. I've also read from Futaba that they recommend the antenna be routed along the top on the airplane.
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Old 08-13-2006, 09:52 PM
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Default RE: Signal Interference

Flyinrain,

You may want to check the spark plug. If your engine requires a resistor plug, ascertain that it, indeed, has a resistor plug installed.
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Old 08-14-2006, 11:15 AM
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ORIGINAL: rlmcnii

flyinrain,

My ZDZ-powered Edge had the same problem. Unfortunately (and this was my foolishness....was having too much fun) this situation ended in a loss-of-control resulting in quite a bit of damage. Do not fly yours until you correct this!

How far does your radio range check? Is it the same with engine running and not running?

I improved my range-check distance by putting buffers on the elevator servos. They are driven from the same channel with a buffer to which two servos can be connected. Originally, the antenna ran along the bottom of the fuselage, parallel to the elevator servo extensions. Now it goes to the top of the vertical stabilizer, no longer parallel to the extensions.. I have been told by radio people that placing an antenna parallel to long extensions can cause reception problems. I do not know if that is true.

Also, i think long extensions may possibly act as antennae and send spurious signals to the receiver. The elevator extensions were originally connected to a non-buffered "Y". This, in effect, created a total extension (including the leads on the servos) of about 60 inches. That is both sides of the "Y" feeding one channel in the receiver.

I have not flown the plane since modifying the radio installation, but it seems better on the ground. It will now repeatedly range check at 55 to 57 yards with the antenna completely collapsed. This distance meets or exceeds the range-check distance specified by FMA. It is a 9C Tx. which has also been tuned to spot-on frequency. Actually, I have been a little reluctant to put this plane back in the air.

The ZDZ has an electronic ignition and it does not seem to be putting out any RF noise.

I have used FS8s very successfully in four other (glow-powered) airplanes with the same transmitter and at the same field.

Does anyone else have experience with FS8s in gas-powered planes (although I don't think the gas engine had anything to do with my trouble)????
Buffers on the servo line will more likely cause interference than reduce it. The buffers are to help the servos get a signal over long lines but since they contain active components they can create spurious signals.
Moving the antenna to the top of the airplane will help.
The ZDZ ignition is well shielded. Just make sure that all connections are tight especially to the sparkplug.

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Old 08-14-2006, 05:57 PM
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Default RE: Signal Interference

Dirtybird,

The buffers were placed in the long elevator-servo extensions at the recommendation of a radio technician and an engineer at FMA Direct.

I am not a radio person. Perhaps the information I received is not accurate.

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Old 08-15-2006, 01:17 PM
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Default RE: Signal Interference

The engineers and technicians at FMA Direct sell buffers. They are not likely to cause interference. But without them you have less sources if you are worried about RF interference.
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Old 08-15-2006, 03:55 PM
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Default RE: Signal Interference

I tend to agree with Dirtybird, in general it is not likely that long servo leads will have any detrimental effect on the reception, in fact may improve it due to the larger counterpoise area (the other half of your antenna). You problem is more likely to small a gauge leads on the power leads (the signal lead can remain a small gauge). Also, a seperate battery supply for the receiver (seperated from the servo power supply) might be your best and easiest fix; i.e. supply the servo bus from its own battery.
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Old 08-15-2006, 07:00 PM
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Default RE: Signal Interference

Rodney,
I believe Flyinrain (I know it is true for me) was having trouble with the loss of the RF link from Tx. to Rx. A "Fail Safe" with an FS8 indicates a loss of reception by the receiver. You seem to indicate that power leads to servos that are of a too-small gauge can cause reception problems. How so?

Also....this question is for everybody....If servo buffers are a potential source of interference, why would anyone use them? In this case, why would FMA recommend a "fix" that could only decrease their customers' satisfaction with their products? I am not a retail merchant, but selling a product that detracts from the performance of your other products makes little sense to me. I understand that there is a $$$ motivation attached to the sale of everything.

Another question comes to mind involving power-management systems. Quest Engineering's Smart Fly comes immediately to mind. Those units provide multiple, FILTERED (buffered), outputs for multiple servos on each channel. These units are above my present level of sophistication, but they seem to be intended for use in high-end, expensive, high-performance, gas-powered airplanes. Are devices such as these detrimental to the successful operation of these airplanes? Does no one use them? Or, have the users of such devices been duped by self-interested manufacturers and vendors?

Does anyone out here in RC cyberspace have any idea of the accurate facts?????



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Old 08-21-2006, 01:25 PM
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Default RE: Signal Interference

I have spent a lot of time talking to the FMA folks and still can’t get things to work. Even though I have a gas engine I’m failing the range test on the ground without the engine running. Since it is magneto shouldn’t cause any issues when not running.

They ask me to conduct a range test with the receiver out of the airplane and the antenna sticking straight up. In that case I was able to go about 270 feet before a failsafe which is great. FMA recommended installing an isolator which I did and no improvement with everything installed in the airplane. My Futaba receiver passes the range test with no problems even without the isolator. FMA says that even with t6he transmitter installed in the airplane it should go long past the minimum of 150 feet which it is not doing. I even installed it in another smaller airplane of mine and didn’t work any better. I’m at a lost of why this is not working
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Old 08-21-2006, 06:00 PM
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Default RE: Signal Interference

Flyinrain,

I noticed with just one servo in my Edge the range check was over 100 yards. With all seven servos connected to the receiver the range check, engine off, is 55 to 57 yards.

Have you had the trancmitter checked for frequency accuracy? I had a Tx. that was out of spec as to its frequency. Apparently they may be out of tolerance when new, and they drift with age.

I'm with you; hard to understand the huge difference between in the plane and out of the plane.

Can anyone explain this?? Has anyone had similar experiences with FMA receivers? Why does the range decrease as the number of servos increases? Or, is this just some fluke????

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Old 08-21-2006, 10:04 PM
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Default RE: Signal Interference


ORIGINAL: rlmcnii

Rodney,
I believe Flyinrain (I know it is true for me) was having trouble with the loss of the RF link from Tx. to Rx. A "Fail Safe" with an FS8 indicates a loss of reception by the receiver. You seem to indicate that power leads to servos that are of a too-small gauge can cause reception problems. How so?

Also....this question is for everybody....If servo buffers are a potential source of interference, why would anyone use them? In this case, why would FMA recommend a "fix" that could only decrease their customers' satisfaction with their products? I am not a retail merchant, but selling a product that detracts from the performance of your other products makes little sense to me. I understand that there is a $$$ motivation attached to the sale of everything.

Another question comes to mind involving power-management systems. Quest Engineering's Smart Fly comes immediately to mind. Those units provide multiple, FILTERED (buffered), outputs for multiple servos on each channel. These units are above my present level of sophistication, but they seem to be intended for use in high-end, expensive, high-performance, gas-powered airplanes. Are devices such as these detrimental to the successful operation of these airplanes? Does no one use them? Or, have the users of such devices been duped by self-interested manufacturers and vendors?

Does anyone out here in RC cyberspace have any idea of the accurate facts?????
Bear in mind that any components added decrease the reliability of the system.
As a design engineer I like to do things in the simplest manner. It creates less headaches. I would never install any of the devices you mention. There is simply no need to in the most advanced airplanes we use. It the servos are heavy drain and come in large numbers the simplest thing to do is increase the size of the wires to them. If the batteries draw down with the application of multiple control orders, increase the size of the batteries.
If you look inside of my airplanes you find just the most basic PCM system. I use PCM because it is a better receiver even though its more costly and complicated. In this case its worth the extra cost and complication.
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Old 08-22-2006, 09:57 AM
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Default RE: Signal Interference

I sent the transmitter to both Futaba then FMA to have it calibrated. It help improve range with my Futaba receiver but not much on the FMA. I’ve tried this with one servo installed and no difference
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Old 08-22-2006, 10:05 AM
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Default RE: Signal Interference

rimcnii, To small a gage wire between the battery and receiver can cause the problems stated; reason, it causes a voltage depression at the power input to the receiver due to IR drop in the wire. The receiver stops working for a few microseconds that the voltage is pulled down below threshold then, the servos stop drawing power, voltage recovers, receiver now sees signal again, servos now draw high current again causing voltage depression and receiver drop out---this continues and servoes appear to be glitching.
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Old 08-22-2006, 11:29 AM
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[/quote]

Bear in mind that any components added decrease the reliability of the system.
As a design engineer I like to do things in the simplest manner. It creates less headaches. I would never install any of the devices you mention. There is simply no need to in the most advanced airplanes we use. It the servos are heavy drain and come in large numbers the simplest thing to do is increase the size of the wires to them. If the batteries draw down with the application of multiple control orders, increase the size of the batteries.
If you look inside of my airplanes you find just the most basic PCM system. I use PCM because it is a better receiver even though its more costly and complicated. In this case its worth the extra cost and complication.

[/quote]

I am also an engineer and can tell you that to say a PCM receiver is better is wrong. If you look at 2 double conversion receivers of the same design one being standart FM and the other PCM decoding they will both have the same sensitivity and selectivity. The decoder section that is in the same case as the receiver is very different but both receivers are the same. If you look at the descriminator of both receivers when at the end of a range check you will see the same thing, degridation of signal. But the decoder section that is fed from the receiver to the output can mask many problems on a PCM receiver.

Another place I would look for the problem in the original post is the switch. I have seen some significant voltage drops in them that you can only see with a scope. Some of the original switches included in new radios and some after market switches should only be used on toys. A bit of resistance there can cause a voltage drop that can only be seen with a scope durring the initial current inrush for loaded servos. This can cause problems in the servos and reset the decoder in the receiver.

Good Luck. I hope you find the problem.

Pete
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Old 08-22-2006, 11:32 AM
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Default RE: Signal Interference

Rodney,

Thanks for the explanation about the servo wire gauge. I use only 20 gauge wire for extensions. Also, use two battery packs for the gasser-Edge, both connected (through switches) directly to the receiver. Battery packs are 2700s with low (when used in parallel) internal resistance.

Perhaps the servo buffers are superfluous. I gather that you fly gassers (as does Dirtybird) and do not use more hardware than absolutely necessary (as does Dirtybird).

I sent my ignition module to RC Showcase for inspection. Apparently it was not functioning properly and must have been..at least intermittently..putting out a lot of noise. Have not yet checked the function of the receiver with the new ignition module. Hopefully that will take care of things.

I wonder what is going on with Flyinrain's receiver.

Anyone out there have any experience with FS8s in gasoline-engined airplanes????

Thanks again! rlmcnii
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Old 08-22-2006, 12:22 PM
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ORIGINAL: modeltronics

]

I am also an engineer and can tell you that to say a PCM receiver is better is wrong. If you look at 2 double conversion receivers of the same design one being standart FM and the other PCM decoding they will both have the same sensitivity and selectivity. The decoder section that is in the same case as the receiver is very different but both receivers are the same. If you look at the descriminator of both receivers when at the end of a range check you will see the same thing, degridation of signal. But the decoder section that is fed from the receiver to the output can mask many problems on a PCM receiver.
Yes the front end of the receiver is the same. However in the late 50's when the RADAR's of the day went to inter pulse coding the signal to noise ratios increased by about 3 db. This is because the decoder was able to read and recognize code further down in the noise than random inputs. A 3db increase in s/n ratio is the same as doubling the transmitter power. Also each pulse data contains its own identification and does not depend on integrety of the frame as PPM does. Since the frame is not synchronized with the engine ignition an ignition interference pulse is not likely to occur in the same pulse twice. The PCM decoder recognizes the bad pulse and throws it out. Some say that the PCM receiver just covers up interference. Yes that is what it does. That is what it was designed to do. With that comes a extra measure of protection. I just set the fail safe to shut the engine off. If I get ignition interference that overwhelms the PCM receiver it shuts the engine off and I get the control back.
I find that my PCM receivers give me about twice the range of my PPM receivers. Are you interested in some used PPM receivers? I'll make you a deal. PM me.
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Old 08-22-2006, 01:01 PM
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