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8 RF Transmitters and Receivers
The radio link is not exactly a part of the project, but one was purchased with the expectation of a possible future R/C project that carried a stereo camera module.
The specific 2.4GHz transmitter/receiver set was selected for several reasons. First, I don't have an FCC license to operate any radio transmitter, second, the 2.4GHz band is becoming more popular, which means more and cheaper equipment is becoming available. On the negative side, that popularity may also pose a problem. Some household appliances, such as microwave ovens, and even some wireless phones, operate in that band, and may cause interference with the video signal. Finally, it was the cheapest radio set that I could find.
The radio was purchased from Circuit Specialists, Inc. (Web-Tronics.com), Item # CSI-HTR2400U, $109 (and on sale for $89). This includes the transmitter, receiver, a power supply for each, and two sets of three audio cables. The radio is designed to be a link for video and stereo audio. While the stereo audio was not implemented in the project, this product could carry the audio part of the stereo video signal.
Figure 56 Hung Chang 2.4GHz Transmitter
The transmitter output is one tenth of a milliwatt of RF power, so it would be a miracle to me if reception is really possible at the advertised distance of 100 meters, even in clear line of sight. Both the receiver and transmitter use a unidirectional antenna. An omnidirectional antenna would be more suitable for an R/C vehicle, unless you expect to have someone to run after it to adjust the antenna at every turn. During one brief test of the unit, the transmitter and receiver were placed about thirty feet apart. The camera and transmitter set up at a window at the rear of the house overlooking the deck, the fence and the houses beyond. The receiver and television were at the opposite end of the house.
Figure 57 Hung Chang 2.4GHz Receiver
Figure 58 Rear View of Transmitter or Receiver (they're identical from the rear)
Even with the antennas oriented toward each other, standing directly in front of the receiver could easily disrupt reception. While some signal noise was noticed, it would not have seriously interfered with controlling a vehicle. Some random snow came and went, and occasionally there were wide white bars of noise. In a mobile unit the directional antenna may need to be controlled somehow - perhaps with an R/C servo. However, if you don't turn it in time, you'll end up not being able to see where you're going... A possible solution would be to make the transmitting antenna omnidirectional, and the receiver unidirectional.
Video quality was much better than I expected, since more signal conversions were added between the cameras and the monitor. During this test, the camera module was used for the first time to view an outdoor scene. The sky was overcast, and there was no washout of the video.
During the test, the camera separation was set at minimum possible - about 2 inches. This minimum setting had been used for "indoor" testing, where the camera was pointed at objects less than six feet away. As described in section 5, close objects should be view with a narrower camera separation to avoid eyestrain. It's a lot like putting your finger tip at the end of your nose, and then trying to bring it into focus. When the camera was pointed at the back yard at the same minimum camera separation, the stereoscopic effect was still very evident at distances of about fifteen to twenty feet.
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