閱讀.....GOOGLE的翻譯越來越有水準
讀後理解
1) 欲接收訊號的頻率 = f1
2) 自己提供的震盪訊號頻率 = f2
3) 輸入 f1 及 f2 到混頻器, 輸出產生兩個頻率訊號 分別為 fo = |f1-f2| 及 fv =|f1+f2|
看看人家的設計是否符合這個簡單的數學加減公式
f1 = 15440 KHz
f2 = 15428 KHz
fo = |15428-15440| = 12KHz
fv = |15428+15440| = 30868 KHz
用 RC 低通濾波器 (LPF), 網上的計算工具以計算, 只保留某部份以下的頻率 (fc),
R = 10K Ohm = 10 x 10^3 Ohm
C = 220 pF = 220 x 10^-12 F
http://en.wikipedia.org/wiki/Direct_conversion_receiver
http://michaelgellis.tripod.com/mixersin.html
Direct-conversion receiver
GOOGLE 翻譯加上俺自己的一些些理解和修改
Direct-conversion receiver
直接轉頻接收器
In telecommunication , a direct-conversion receiver (DCR), also known as homodyne , synchrodyne , or zero-IF receiver , is a radio receiver design that demodulates the incoming signal by mixing it with a local oscillator signal synchronized in frequency to the carrier of the wanted signal.
在無線通訊, 直接轉頻接收器 (DCR), 也被稱為零差，synchrodyne, 或稱為 [零中頻接收器], 是其中一種無線電接收器設計, 輸入信號的解調, 一個為輸入信號, 另一個為本地震盪訊號 (與發送頻率 -載波 carrier), 透過混頻電路 (MIXER) 而得到傳送的訊息.
The wanted modulation signal is obtained immediately by low-pass filtering the mixer output, without requiring further detection .
混頻器的輸出, 經過低通濾波器 (low-pass filter, LPF), 而無需進一步的檢測就可以得希望訊號.
Thus a direct-conversion receiver requires only a single stage of detection and filtering, as opposed to the more common superheterodyne receiver design, which converts the carrier frequency to an intermediate frequency first before extracting the modulation, and thus requires two stages of detection and filtering.
因此，一個 [直接轉頻接收器] 只需要單一階段的檢測和濾波. 比對通常的 [超外差接收器設計], 載波頻率需要先轉換到中頻, 然後才做解調, 因此需要兩個階段的檢測和過波.
* 1 Properties 1 屬性
* 2 History and applications 2 歷史和應用
* 3 See also 3另 見
* 4 External links 4 外部鏈接
Unwanted signals are left on carriers of the frequency difference between their original carrier and that of the wanted signal.
不需要的信號仍然存在於 載波頻率和欲接收訊號之中.
There is no detection of the unwanted signals since the whole signal path is kept free of non-linearity.
對不需要的信號沒有做任何檢波, 因為整個信號通路保持一至性
Unwanted signals can be completely rejected by use of a low-pass filter on the audio output.
音頻輸出, 經過低通濾波器 (LPF) 可以完全過濾不需要的信號.
The receiver consequently has the advantage of high selectivity , and is inherently a precision demodulator.
因此是精確解調器, 擁有良好的選擇性.
The principles can be extended to permit separation of signals whose sidebands overlap, and they also lead to improved detection of pulse-modulated signals.
這些原則可以擴展到允許分離信號的邊重疊, 他們也導致改進檢測的脈衝調製信號。
The homodyne was developed in 1932 by a team of British scientists searching for a method to surpass the superheterodyne .
零差開發於1932年由一個英國科學家小組在尋找一種方法來超越超外差設計.
This new type of receiver was later renamed the synchrodyne, and not only proved to have superior performance, but the single conversion stage also had lower complexity and power consumption.
這種新型的接收機, 後來改名為 synchrodyne，不僅證明具有優越的性能, 同時兼具設計簡單, 省電的優點.
But the circuit after a period of time became unstable due to slight drift in frequency of the local oscillator .
使用時溫度升高, 本地振盪器頻率輕微改變 (輕微頻率漂移), 讓電路變得不穩定. 缺點其一.
To counteract this drift, the frequency of the local oscillator was compared with the input by a phase detector so that a correction voltage would be generated and fed back to the local oscillator, thus keeping it on lock.
為了對付這種頻率漂移，振盪器加上相位自動校正, 保持頻率穩定.
This type of feedback circuit evolved into what is now known as a phase-locked loop .
這種類型的反饋電路演變成現在稱為鎖相環 。
While the method has existed for several decades, it had been difficult to implement due largely to component tolerances , which must be very tight for this type of circuit to operate well.
雖然該方法已存在 60年, 它一直難以實施, 主要由於零件公差, 這種電路的運作良好仰賴精確的零件.
The circuit was not without other problems.
這種電路並非沒有其他問題。
Reverse-transmission paths can occur in the receiver.
反向傳輸路徑可以發生在接收器。
Local-oscillator energy can leak through the mixer to the antenna input and then re-enter the mixer.
本振洩漏能量可以通過混頻器的到達天線輸入端, 然後重新輸入到混頻器.
The overall effect is that the local oscillator energy would self-mix and create a DC offset .
宏觀而言, 本地振盪器能源將自我組合, 產生一個直流偏移.
The offset could be large enough to swamp the baseband amplifiers and destroy signal reception.
偏移量可以大到足以淹沒基帶放大器和破壞的信號接收.
There were several work arounds to deal with this issue but these too added to the complexity of the receiver.
有幾個變通的手段來處理這些問題, 但同時也增加了接收器的複雜性.
Ultimately the higher costs were found to outweigh the benefits.
最終的成本越來越高，發現得不償失.
The widespread use of this principle did not begin until the development of the integrated circuit and incorporation of complete phase-locked loop devices in low-cost IC packages.
直到專用的集成電路, 並納入完整鎖相環器件在低成本IC封裝內, 這種設計才開始廣泛使用.
These are no longer limited to the reception of AM radio, now being able to process more complex modulation schemes.
這種電路已不再侷限於調幅接收機應用, 目前能夠處理更複雜的調製方案.
Since then, direct-conversion receivers have been incorporated into many receiver applications, including cellphones , televisions , avionics and medical imaging apparatus.
因此, 直接轉頻接收器被很多無線電接收器設計採用, 包括手機, 電視, 航空電子設備和醫療成像設備。
* Crystal radio receiver 礦石無線電接收機
* Directly amplifying receiver 直接放大接收器
* Reflectional receiver 反射式接收機
* Homodyne detection 零差檢測
* Low IF receiver 低中頻接收機
* Neutrodyne Neutrodyne
* Regenerative radio receiver
* Superheterodyne receiver 超外差接收機
* Tuned radio frequency receiver 調諧射頻接收機
讀後理解
1) 欲接收訊號的頻率 = f1
2) 自己提供的震盪訊號頻率 = f2
3) 輸入 f1 及 f2 到混頻器, 輸出產生兩個頻率訊號 分別為 fo = |f1-f2| 及 fv =|f1+f2|
看看人家的設計是否符合這個簡單的數學加減公式
f1 = 15440 KHz
f2 = 15428 KHz
fo = |15428-15440| = 12KHz
fv = |15428+15440| = 30868 KHz
用 RC 低通濾波器 (LPF), 網上的計算工具以計算, 只保留某部份以下的頻率 (fc),
R = 10K Ohm = 10 x 10^3 Ohm
C = 220 pF = 220 x 10^-12 F
fc = 1/3.14 / (10 x 10^3 Ohm x 220 x 10^-12 F)
fc = 72KHz
正確..
所以, 如果要換到接收 810KHz 的訊號, 應該有眉目了, 這也應該是老外或這位仁兄 (BX2AW) 建議用 822KHz XTAL 的原因了. 另外還請教或參考如 YC, 翁先生, 以及幾個老外...
到此手上兩個方案,
1) 等老外帶來的 SDR, 買 3.200 或 3.280 MHz XTAL, 4 除頻後得到約 800KHz, 混頻後大概 12KHz, 在改以改 LPF, 適應 12KHz, 就可以玩樂.
2) 沿用以下這個 DCR, 自己改 XTAL, 用822KHz, 礦石天線或 LOOP 天線, 就可以實驗.
可是到今天還是沒有在香港的朋友聽過這個電台的廣播.........%$#@#$
http://en.wikipedia.org/wiki/Direct_conversion_receiver
http://michaelgellis.tripod.com/mixersin.html
Direct-conversion receiver
In telecommunication, a direct-conversion receiver (DCR), also known as homodyne, synchrodyne, or zero-IF receiver, is a radio receiver design that demodulates the incoming signal by mixing it with a local oscillator signal synchronized in frequency to the carrier of the wanted signal. The wanted modulation signal is obtained immediately by low-pass filtering the mixer output, without requiring further detection. Thus a direct-conversion receiver requires only a single stage of detection and filtering, as opposed to the more common superheterodyne receiver design, which converts the carrier frequency to an intermediate frequency first before extracting the modulation, and thus requires two stages of detection and filtering.
....................................
GOOGLE 翻譯加上俺自己的一些些理解和修改
Direct-conversion receiver
直接轉頻接收器
In telecommunication , a direct-conversion receiver (DCR), also known as homodyne , synchrodyne , or zero-IF receiver , is a radio receiver design that demodulates the incoming signal by mixing it with a local oscillator signal synchronized in frequency to the carrier of the wanted signal.
在無線通訊, 直接轉頻接收器 (DCR), 也被稱為零差，synchrodyne, 或稱為 [零中頻接收器], 是其中一種無線電接收器設計, 輸入信號的解調, 一個為輸入信號, 另一個為本地震盪訊號 (與發送頻率 -載波 carrier), 透過混頻電路 (MIXER) 而得到傳送的訊息.
The wanted modulation signal is obtained immediately by low-pass filtering the mixer output, without requiring further detection .
混頻器的輸出, 經過低通濾波器 (low-pass filter, LPF), 而無需進一步的檢測就可以得希望訊號.
Thus a direct-conversion receiver requires only a single stage of detection and filtering, as opposed to the more common superheterodyne receiver design, which converts the carrier frequency to an intermediate frequency first before extracting the modulation, and thus requires two stages of detection and filtering.
因此，一個 [直接轉頻接收器] 只需要單一階段的檢測和濾波. 比對通常的 [超外差接收器設計], 載波頻率需要先轉換到中頻, 然後才做解調, 因此需要兩個階段的檢測和過波.
* 1 Properties 1 屬性
* 2 History and applications 2 歷史和應用
* 3 See also 3另 見
* 4 External links 4 外部鏈接
Unwanted signals are left on carriers of the frequency difference between their original carrier and that of the wanted signal.
不需要的信號仍然存在於 載波頻率和欲接收訊號之中.
There is no detection of the unwanted signals since the whole signal path is kept free of non-linearity.
對不需要的信號沒有做任何檢波, 因為整個信號通路保持一至性
Unwanted signals can be completely rejected by use of a low-pass filter on the audio output.
音頻輸出, 經過低通濾波器 (LPF) 可以完全過濾不需要的信號.
The receiver consequently has the advantage of high selectivity , and is inherently a precision demodulator.
因此是精確解調器, 擁有良好的選擇性.
The principles can be extended to permit separation of signals whose sidebands overlap, and they also lead to improved detection of pulse-modulated signals.
這些原則可以擴展到允許分離信號的邊重疊, 他們也導致改進檢測的脈衝調製信號。
The homodyne was developed in 1932 by a team of British scientists searching for a method to surpass the superheterodyne .
零差開發於1932年由一個英國科學家小組在尋找一種方法來超越超外差設計.
This new type of receiver was later renamed the synchrodyne, and not only proved to have superior performance, but the single conversion stage also had lower complexity and power consumption.
這種新型的接收機, 後來改名為 synchrodyne，不僅證明具有優越的性能, 同時兼具設計簡單, 省電的優點.
But the circuit after a period of time became unstable due to slight drift in frequency of the local oscillator .
使用時溫度升高, 本地振盪器頻率輕微改變 (輕微頻率漂移), 讓電路變得不穩定. 缺點其一.
To counteract this drift, the frequency of the local oscillator was compared with the input by a phase detector so that a correction voltage would be generated and fed back to the local oscillator, thus keeping it on lock.
為了對付這種頻率漂移，振盪器加上相位自動校正, 保持頻率穩定.
This type of feedback circuit evolved into what is now known as a phase-locked loop .
這種類型的反饋電路演變成現在稱為鎖相環 。
While the method has existed for several decades, it had been difficult to implement due largely to component tolerances , which must be very tight for this type of circuit to operate well.
雖然該方法已存在 60年, 它一直難以實施, 主要由於零件公差, 這種電路的運作良好仰賴精確的零件.
The circuit was not without other problems.
這種電路並非沒有其他問題。
Reverse-transmission paths can occur in the receiver.
反向傳輸路徑可以發生在接收器。
Local-oscillator energy can leak through the mixer to the antenna input and then re-enter the mixer.
本振洩漏能量可以通過混頻器的到達天線輸入端, 然後重新輸入到混頻器.
The overall effect is that the local oscillator energy would self-mix and create a DC offset .
宏觀而言, 本地振盪器能源將自我組合, 產生一個直流偏移.
The offset could be large enough to swamp the baseband amplifiers and destroy signal reception.
偏移量可以大到足以淹沒基帶放大器和破壞的信號接收.
There were several work arounds to deal with this issue but these too added to the complexity of the receiver.
有幾個變通的手段來處理這些問題, 但同時也增加了接收器的複雜性.
Ultimately the higher costs were found to outweigh the benefits.
最終的成本越來越高，發現得不償失.
The widespread use of this principle did not begin until the development of the integrated circuit and incorporation of complete phase-locked loop devices in low-cost IC packages.
直到專用的集成電路, 並納入完整鎖相環器件在低成本IC封裝內, 這種設計才開始廣泛使用.
These are no longer limited to the reception of AM radio, now being able to process more complex modulation schemes.
這種電路已不再侷限於調幅接收機應用, 目前能夠處理更複雜的調製方案.
Since then, direct-conversion receivers have been incorporated into many receiver applications, including cellphones , televisions , avionics and medical imaging apparatus.
因此, 直接轉頻接收器被很多無線電接收器設計採用, 包括手機, 電視, 航空電子設備和醫療成像設備。
* Crystal radio receiver 礦石無線電接收機
* Directly amplifying receiver 直接放大接收器
* Reflectional receiver 反射式接收機
* Homodyne detection 零差檢測
* Low IF receiver 低中頻接收機
* Neutrodyne Neutrodyne
* Regenerative radio receiver
* Superheterodyne receiver 超外差接收機
* Tuned radio frequency receiver 調諧射頻接收機
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