RC transmission through water using tether - Page 2 - RC Groups
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Oct 12, 2012, 05:14 PM
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With the RX moved away from the surface and connected to the TX output by a wire (preferably a coax to eliminate interference), there will be losses and reduction of signal, usually expressed as so many dB/metre at a given frequency for a particular cable. I would normally expect to need some sort of signal booster to send a viable control signal 30 metres down a cable, whatever band was in use.
However, if the TX output is feeding the cable without going through the air, it is quite likely that attenuation will be needed to avoid the RX input being overloaded. This would probably be best at the RX end of things, to minimise any noise interference problems. The RX tuning tries to reject out-band signals (interference), attenuating a big signal also reduces any interfering noise. Win-win.
Using different cables, its anybody's guess until it's tried, especially when using the gear away from it's original intended use, but once a working setup is hit, it will be found that there is quite a big operating window due to the wide range of acceptable input voltages that the RX is designed to work with - standing over it to so far away that you are guessing which way the boat is facing.
Apart from the familiar layout of a commercial TX, I would be tempted to use an RS232 or USB link with an encoder to send and a decoder to act as a receiver. If headed to CAT5, thats network cable. PC type devices spring to mind like Arduino and Raspberry Pi to receive and sort out the incoming signals, maybe a cheap tablet to be the control panel. If the multi way cable suggested has enough cores, there is no need for the radio - the servos & ESCs could be controlled from servo testers, of which there are plenty of circuits on the internet. The radio is just a way of multiplexing a bunch of signals together, then separating them out again in the right order at the other end.
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Oct 12, 2012, 06:16 PM
NeverAgainVolunteerYourse lf
nick_75au's Avatar
This is something I would not know how to make work (and forgive the lack of proper RF terminology ) but the RF deck is fed the PPM signal, If you disabled the RF deck and fed the PPM signal direct to the CAT 5, then figured out where the RF in the receiver converts back to PPM and feed the CAT 5 wire into that point. maybe no attenuation would be required and perhaps the PPM signal would be a suitable form to not need shielded wire.

I vaguely remember using the trainer port PPM signal and feeding that to the co-ax and having it work< it was a good while ago and would need some experimentation


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