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Execration

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About Execration

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  1. The results of the shielding aren't very good. I got everything out to test and my range check couldn't even pass 10 feet! Alright, so I knew something was obviously wrong, and re-arranged some wires to get it roughly back to 'normal'. my range was still reduced when the speed controller was on though. I eventually narrowed teh problem down to the wire that goes from the speed controller (front, next to 900Mhz Tx) to the receiver in the tail. The really strange part about all this is my range is fine when the speed controller is OFF, but that wire is still connected. Once the speed controller is switched on, I get reduced range. This is why I assumed that wire was not the cause of my problem. A colleague and I were playing around with the wire, and noticed that there was a sweet spot, that when moved into, resulted in no noticeable range reduction. Moving the wire as little as an inch was the difference between full range and half range. I still haven't figured this out completely, it's actually driving me insane, but I have a few things to try: 1. Complete shielding of this wire from ESC to receiver, using aluminized duct tape to enclose it along the outside of the fuselage, isolated from everything possible. It will be grounded to an appropriate spot (whatever works) and will have a network of ferrite beads, aluminum firewall, and capacitors to try and eliminate any pesky RF. 2. Use an opto-isolator with a run of fibre-optic cable to make the connection, since there is only the signal wire (throttle signal) and a ground. Only one fibre will need to be run. 3. Low-pass filter on the 900Mhz Tx to try to elminiate any emitted unwanted RF. So far I have no evidence of overtones or the 900Mhz signal getting into the receiver via the antenna; most problems seem to be noise entering the receiver by means of the servo leads. Until I do a full range test (when I get rid of the noisy servo leads) I won't know if the 900Mhz is really swamping my 2.4Ghz receiver. Naturally, I can't perform this full range test until my small-scale attenuated range-check passes. I'm getting closer, but not quite there yet.
  2. Details about the aircraft I am using can be found here: http://www.resonance.on.ca/Mike%20UAV%20Bu...ter%20Build.htm This wireless video issue is becoming a real pain; I am thinking of moving to a different video Tx if a low-pass filter is impractible or it doesn't work at all. I am still looking into it. I did some extensive shielding yesterday and am ready for some more testing. Hopefully I'll see some results today.
  3. Lupy - My video Tx is indeed a Mobicomm from eBay. I've spoken to the man behind the transmitter, and he is a very knowledgeable and helpful guy. Unfortunately, it seems that these transmitters are pretty noisy if you are indeed having the same problems. I know it is interfering with the XtremeLink 2.4Ghz module, but I haven't yet tried my expensive JR 72Mhz PCM receiver, which I will get around to eventually. I suppose the same thing will happen. Once I shield everything in the aircraft (doing that as we speak) and getting rid of the interference caused by the speed controller being so close to the video transmitter, I'll test the system and see my actual range reduction. I'll post some pics as well for everyone to see. I am hoping I will be successful. Bear - The purpose of this aircraft is to be cheap, since conventional UAVs run in the 10s of thousands of dollar range. We are also developing a GPS system to guide the aircraft, but this is more of a return to home feature if the uplink or downlink fails. I'm not sure how far this will go, but thanks for the links.
  4. OK, another update. After fooling around with some wiring, I was able to eliminate my problem. My switch harness for the radio was too close to the main battery and camera wires, and in that jumbled mess something was causing interference. After moving it away, the problem was relieved. I went to a large open field with no obstacles around and after doing a range test, I noticed no difference in my radio's performance whether the 900Mhz was on or not! I walked about 147 steps away from the aircraft, to the point where I couldn't see the tail deflection anymore, then marked the spot. I then walked to the same spot with the 2 Watt 900Mhz Tx on and it worked perfectly. HOWEVER, this test was done without the speed controller connected, since I was alone and didn't have the aircraft tied down, and if interference were to occur I didn't want to risk my aircraft flying away on me. Today I plugged the speed controller in, and revved the engine. Everything seemed good. Even the camera's picture was near perfect, seemingly unaffected by all the noise present. A range check, though, showed that some major interference was occuring. I narrowed it down to the speed controller. After looking more closely, I noticed that the only wire going to my receiver from the very nose of the plane is from the speed controller. On top of that, the power lines to my motor are travelling right around (touching) my 2 Watt Tx and coming within centimetres of the antenna. After seeing the importance of proper placement and shielding, and realizing RF isn't like Bigfoot after all (I assumed everyone was afraid of it - but it was rarely seen hehe), I am shielding every wire in the aircraft to ground, and installing an RF choke on the lines entering the receiver. Copper braid will be used for shielding. I am confident this will solve the problem. My ultimate range, however, will only be tested when I can get an area of 4-5 km line-of-site. I will update when I do this.
  5. Thanks for the response guys. I haven't updated this thread for a while because I've been so busy. I followed Doofer's advice and put the receiver and servos in the tail, with CoPilot back there as well and the IR sensor on the tip of the tail. I have two wires running from the tail section to the midsection; one is to the receiver battery pack, and the other is to the ESC at the very nose. I made these twisted pair to help with any noise. My 2 Watt 900Mhz Tx is located in the nose, antenna pointed down. It is tapping into the main battery packs that the ESC uses to supply my motor and the BEC for my mini camera. The ONLY link between these two systems is the wire from my receiver to the ESC, and since the ESC is supplying the camera, which is connected to the 900Mhz Tx... it could potenetially be a problem but not likely. I shielded my 2.4 Ghz receiver with copper tape, and I soldered all the joints together. I then grounded this shield to the battery pack. The antenna, of course, is not shielded, so there is an area surrounding its base where some noise could leak in I suppose. I opened the receiver module itself and there is indeed a shielded box inside. Other circuits are still exposed, however. I tested this modified setup today and found that I had much better range than before. The test was quick, in a noisy environment with lots of cars and overhead wires, so it probably isn't entirely accurate. I still notice a slight range reduction, but I'm not sure how relevent it is. For example, if I can get 150 feet from the aircraft (with my transmitter antenna removed and power attenuated at 10%) with the 900 Mhz off, I can get 140 - 145 feet with the 900 Mhz on. There is definitely a reduction in signal quality though, and I suppose if this was a full range test (coming soon) I might lose a range of almost a kilometer, but we'll see. I am going to add some more shielding and move things around for further tests, and if any of you have anymore suggestions I will be glad to try them. I might be putting a low-pass filter on my 900Mhz, I'll look around for one. Is there an easy way to attenuate the power to 1 Watt instead of 2? Even if just for testing, since I can always order another 1 Watt Tx instead of 2 Watt if need be.
  6. I've already thought of that idea, and while it does help (inverse square law), it doesn't solve the problem. Remeber, I need as much range as possible, since I require 4-5 km! Any other ideas? Could the servo extensions act as antennas and pick up the RF? If so, can anything be done to prevent this? Could the 2.4 Ghz receiver be shielded somehow without shielding the 2.4 ghz signal itself?
  7. As part of my current job, I am in charge of putting together a R/C aircraft capable of being video-piloted 4-5km (3-4 miles) via line-of-site. It will carry scientific instruments over sites that are normally hard to get to, such as the terrain surrounding the peak of a volcano. To accomplish this goal, a 2.4 Ghz XtremeLink uplink was chosen due to its advertised 5 mile range. This is the only off-the-shelf system that could potentially supply the range I need. So far we’ve tested it to 4.5 km on the ground (after 4.5 km line-of-site was lost), beside a highway where there are lots of obstacles and potential sources of interference such as power lines etc. The downlink chosen was a 900 Mhz 2-Watt video transmitter. The base station is using an 8 dBi patch antenna, which should be more than enough to cover a 5 km range. Here is where my problem starts. When I went to range-check my 2.4 Ghz radio with the 900Mhz transmitter turned on, I was unable to get more than 50 feet away at full power before I lost total control. This is MAJOR interference. I was puzzled, especially considering the separation of the two frequencies. A normal range check consists of unscrewing the 2.4 Ghz antenna on the Tx, and holding a button which reduces the output power to 10%. You are then supposed to be able to get at LEAST 50 feet (150 reported by some) from the aircraft before transmission is cut off. I couldn’t even make it 50 feet with antenna on and full power, let alone 5 km! I need help in troubleshooting this interference problem. The first thing I did was try separating all the wires and components from each other, outside the aircraft in a test area. I noticed that if any servo wires came too close to the 900 Mhz antenna, the servos would lock up to one side and wouldn’t respond until at least 5 inches of separation was given. Once separated, they worked flawlessly. After separating the 900 Mhz transmitter and its power supply from the 2.4Ghz receiver and its power supply, with no wires crossing each other, the range was significantly increased. I could now successfully perform a range check, and probably fly successfully as long as I wasn’t flying first-person. However, the range check indicated that my control crapped out sooner with the 2 Watt video Tx on that without. In other words, the 900 Mhz is still causing interference, just not as bad. If I am going to fly 4-5km however, this interference cannot be ignored, especially if a range reduction is noticed on the ground. My goal here is to have both of these components operating with each other such that no impact can be detected if the 900Mhz Tx is on or off. I will now detail my exact setup for further clarification. For my uplink, I have the 2.4 Ghz receiver with its own dedicated battery. The elevator and rudder outputs are fed into a Co-Pilot stabilization system. This device takes readings from an attached IR sensor and adds control inputs to the rudder and elevator to keep the aircraft completely level during flight. Servo extensions are used, but they can be eliminated if need be. The transmitter is running off the main battery pack. A DC-DC Converter is used to regulate the 14.8V 4-cell lithium batteries to 12V. Long power lines are used to reach the Tx, which is mounted just past the trailing edge of the wing. The colour KX131 camera is being supplied a regulated 5V power supply from the unused BEC of the speed controller, and thus is also running off the main batteries. A coaxial cable is taking its output and feeding it into the 2 watt Tx via an RCA cable. I originally had a lot of wires passing each other, and I am blaming that configuration for my initial, horrible range. After the components were separated, and kept as ‘modules’ (Tx and Rx separated), the range greatly increased, however it’s still not as good as when the 2 watt 900 Mhx Tx is turned off. Is there anything that can be done to stop this interference? My boss suggests it isn’t the 2.4Ghz receiver antenna picking up the 900 Mhz signal, since it works, just only up to a certain range. He says perhaps the pre-amp or diode arrays in the receiver are being saturated by the 900 Mhz RF. Perhaps a set of in-line filters or some shielding could prevent this? Please see the attached images for further clarification of my setup. Any help is greatly appreciated, thanks.
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