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。

Very informative!!  Can put on the top list!!  

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，接收高放電路先將收取得來的２７．１９５ｍｈｚ經ｐｈａｓｅ　ｌｏｃｋ　ｌｏｏｐ　ｃｉｒｃｕｉｔ，加入ｌｏｃａｌ　ｏｓｃｉｌｌａｔｏｒ整出來的１６．４９５ｍｈｚ（接收晶體），ｓｉｇｎａｌ經　ｍｉｘｅｒ同ｆｉｌｔｅｒ　選出１０．７ｍｈｚ，經中放電路放大再係ｍｉｘｅｒ加入ｌｏｃａｌ　ｏｓｃｉｌｌａｔｏｒ整出來的１６．０４ｍｈｚ（內置接收晶體）SIGNAL，　ｓｉｇｎａｌ經　ｍｉｘｅｒ同ｆｉｌｔｅｒ　選出４５５ｋｈｚ，再經中放電路放大到......低放．．．．．．．最後ｄｅｃｏｄｅ

ｓｉｎｇｌｅ　ｃｏｎｖｅｒｓｉｏｎ　（同ａｍ一樣）
如果發射係２７．１９５ｍｈｚ，接收高放電路先將收取得來的２７．１９５ｍｈｚ經ｐｈａｓｅ　ｌｏｃｋ　ｌｏｏｐ　ｃｉｒｃｕｉｔ，加入ｌｏｃａｌ　ｏｓｃｉｌｌａｔｏｒ整出來的２６．７４ｍｈｚ（接收晶體），ｓｉｇｎａｌ經　ｍｉｘｅｒ同ｆｉｌｔｅｒ　選出４５５ｋｈｚ，經中放電路放大到..........低放．．．．．．．最後ｄｅｃｏｄｅ

其他野都係唔ｏ係度講．．．講左都無人知咩離

[ 本帖最後由 ice1234 於 2007-9-19 10:45 編輯 ]

原帖由 ice1234 於 2007-9-18 21:28 發表

                               
登錄/註冊後可看大圖

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 ]

Can it be more "complicated in, simple out"     thanks!

原帖由 gibson 於 2007-9-18 10:02 PM 發表

                               
登錄/註冊後可看大圖

Can it be more "complicated in, simple out"     thanks!

電子野正是那麼complicated ...

thx ryan
簡單一句
fm 無得潛水

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....

好！絕頂玩車冷知識

原帖由 ryancmlam 於 2007-9-18 11:00 PM 發表

                               
登錄/註冊後可看大圖

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....

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 ,however if u swap RX AND TX ,the efficiency of RC system will be reduced.

FM dual conversion system can't swap their RX TX,because of the unwanted is so far away from the wanted signal ("21.4mhz"), it can easily to filtered out of this unwanted signal by using suitable filter.Thus,FM dual conversion system can't swap their RX TX.

BTW, some "非貴價" like E-SKY ($120) , they also develop their FM receiver  based on dual conversion type.

[ 本帖最後由 ice1234 於 2007-9-21 11:42 編輯 ]

原帖由 ice1234 於 2007-9-20 10:54 發表

                               
登錄/註冊後可看大圖

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....

原帖由 ryancmlam 於 2007-9-20 11:36 PM 發表

                               
登錄/註冊後可看大圖

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

http://www.rc711.com/shop/produc ... amp;products_id=189

[ 本帖最後由 ice1234 於 2007-9-27 10:50 編輯 ]

收音機 :
AM    I.F. Frequency : 455KHz
FM    I.F. Frequency : 10.7MHz

RC :
AM   I.F Frequency : 455KHz
FM ( PPM & PCM )   I.F Frequency : KO , Futaba , SANWA ,JR 間間厰都不同 . PCM 同 PPM 嘅 I.F. 都唔同 , 若果相同嘅話的 X'TAL 可以撈亂用啦但事實上用唔到吖嗎 ..............

原帖由 Panda 於 2007-9-21 11:41 AM 發表

                               
登錄/註冊後可看大圖

收音機 :
AM    I.F. Frequency : 455KHz
FM    I.F. Frequency : 10.7MHz

RC :
AM   I.F Frequency : 455KHz
FM ( PPM & PCM )   I.F Frequency : KO , Futaba , SANWA ,JR 間間厰都不同 . PCM 同 PP ...

Aｌｔｈｏｕｇｈ，　they have same IF frequency and same conversion ,FM transmitters are not always compatible with receiver from other manufactuter,as the frequency shift from a 0 to 1 can either be positive or negative..

咁. 潛水有咩用..(rx 同 tx 對換插)?

Dual conversion, what is the advantage over single conversion?