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Subject: interference and phase shift in RC

Date: 02/28/03 at 1:01 AM
Posted by: janet
E-mail: janet_smith2000@yahoo.com
Message Posted:

http://www.pfmax.com/temp/fig2.gif

fig2

http://www.pfmax.com/temp/fig3.gif

fig3

Hi,

I m using 27MHz Tx/Rx. Initially my antenna is designed to be floated on the water surface to have a better quality of receiving signal. however, refer to fig 3, when the RF signal (EM signal) travels through 2 different mediums, there's always a phase shifting between the signal in the 1st medium and the signal in the 2nd medium. And reach the receiver at different time.

in refer to fig 2. the wave path may go
1. Tx -> air -> floating antenna -> Rx.
2. Tx -> air -> water -> antenna wire/surmarine body -> Rx.

the two wave paths may produce a phase difference with each other.
These 2 wave will act like a 2 different sources and they may be interfere with each other at the receiver.

1) Is this effect negligible? will this phenomenon falsely trigger my system when receiving signal?

I myself have come up 2 solutions: 1. remove the floating antenna, so all the received-signal go through the same path Tx -> water -> antenna -> Rx. However, the RF signal can't go very deep under the water. 2. by putting a special coating on the surface of submarine body and the wire, so the signal can't go through submarine body. But,
I don't know what kind of the coating it is. Do you have a better solution for this problem?

2) Do i need a PLL(Phase-Lock-Loop) circuit? My Tx/Rx is Amplitude Modulated.

3) Is that posible to calculate the phase-shift under the water? since the signal may go in different direction.

4) How to ensure the antenna i use will not rusted away by the water? I have noticed that the antenna of some submarine toys is plastic coated, so do the antenna of handphone. The radio in my house is using a wire-like antenna, rather than the steel-made rod.

5) Will Doppler Effect take place in our Radio control system?


6) How to fabricate/make a controller casing? i wish to have several buttons on my controller.
pls give me some guidance. thank you!


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