潛水 Q&A

Just want to share our "discussion" in the TKO offroad party regarding 潛水. Pls feel free to correct if I am wrong.

Q1. What is 潛水 ?
A1. rx 同 Tx 對掉就o.k. 也叫做潛水.

Q2. 我rx同tx一樣樣, 冇分ga wor?
希望可以簡單explain一下。
一般RC系统的接收晶体(Rx)的frequency是比發射晶体(Tx)低0.455Mhz的。e.g. If Tx is 27.145Mhz, Rx would be 27.145-0.455=26.69Mhz(note:印刷在Rx上的數字是說明它是配合那個Tx，不是說它本身的frequency，你可看看刻在晶体的數字)。但是一般簡單(非貴價)RC系统的接收機也會同時解讀比Tx高0.455Mhz的訊號e.g. If Tx is 27.145Mhz而接收機的晶体是27.145+0.455=27.6Mhz的話，整個RC系统也可運作。Similarly，若你的發射晶体是26.69Mhz，而接收晶体為27.145Mhz(即"潛水")，整個RC系统也可運作

Q3. 我的band is AM 27.195 ，如果玩"潛水", TX 便變成 26.740，但是車的RX變成 27.195，那麼Receiver是不是會同時受到 "27.195 or 27.650 Controller" 的控制 ?

A3.If the crystal in your receiver is 27.195 Mhz.
- It will NOT be controlled by a transmitter with Tx = 27.195, but
- It will be controlled by a transmitter with Tx = 27.195+0.455=27.650Mhz and by the side-band i.e. Tx=27.195-0.455=26.740Mhz.
So Receiver是會同時受到 27.650 and 26.740 Mhz Controller 的控制

Q4. 點解Rx要比Tx低0.455Mhz的 ?

A4. I try to explain it in a simple way.
Transmitter的訊號頻率e.g.27.145Mhz是指"載住"控制訊號的頻率。而控制訊號本身的頻率通常底於27.145Mhz很多。在Transmitter運作時，它會把"控制訊號"加進"搭載訊號"(=27.145Mhz)頻率中而成為發射訊號。當receiver收到發射訊號後，它會利用本身crystal的頻率(26.69Mhz)把搭載訊號從發射訊號減走，取得控制訊號。非高價receiver通常冇分走負數，因此正負都要i.e.(26.96+0.455=27.145Mhz) or (26.96-0.455=26.235Mhz)也同時被當作發射訊號。

原帖由 ice1234 於 2007-9-18 21:28 發表

                               
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唔係對對ｂａｎｄ都係差４５５ｋｈｚ
好似ｆｍ咁
有分ｄｕａｌ　ｃｏｎｖｅｒｓｉｏｎ同ｓｉｎｇｌｅ　ｃｏｎｖｅｒｓｉｏｎ
前者晶體頻率差１０．７ｍｈｚ．．．如果發射係２７．１９５ｍｈｚ，接收高放電路先將 ...

Yes. That's why I bold "非貴價". i.e. single conversion.

Dual conversion system shoud not 潛水 (in fact, cannot). Am I right ? (I just guess and didn't try before, of course, haven't check the reference book)

BTW, do you know which model of RC receiver is dual conversion ?

[ 本帖最後由 ryancmlam 於 2007-9-18 21:44 編輯 ]

I think it could be if the FM is a single conversion system. However, I don't know and haven't checked. I just know that AM is, because of .... cheap....

原帖由 ice1234 於 2007-9-20 10:54 發表

                               
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YES,only AM and FM  single conversion system can use  潛水  ,because the unwanted image signal is so closed to wanted signal(only 910khz),it is difficult to filtered out of this unwanted signal ,h ...

Probably my knowledge is out of dated now. How come a cheap cheap Esky receiver could be dual conversion....