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Registered Member #929
Joined: Sat Jul 28 2007, 06:14PM
Location:
Posts: 3
Thanks for the response guys. I haven't updated this thread for a while because I've been so busy. I took some steps 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 (motor speed controller) 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 potentially 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.
Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
Just a thought - is it possible that you are "detecting" the 900 MHz signal as an error signal in the servos? Rectification of the RF signal through various junctions in the servo system can result in a DC offset that causes positional or velocity offsets -either/both can disrupt normal operation of the servo loop. I've seen this occur in industrial servos when a handheld transmitter was turned on close to the servo control hardware.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You mentioned you had two wires going from the receiver in the tail to the midsection. Try sticking those wires through a smallish ferrite ring, located right next to the receiver.
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900 Mhz Video Downlink Interfering with 2.4 Ghz Uplink
