價格包絡線（或稱百分比通道）是按照固定百分比設置在移動平均線上方和下方的兩條通道線。它們可以單獨顯示超買、超賣水平，也可以與動能指標結合起來使用。移動平均線可以根據所交易週期設置，百分比的大小應該將90%的價格波動包含在通道内為宜。如果價格波動隨著時間的推移變得劇烈，則應適時調整通道線的百分比。
交易信號
首先，確認價格是處於趨勢中還是調整期：
• 如果價格在移動平均線週圍波動，則說明處於調整期。
• 價格在移動平均線上方運動，則處於上升期。
• 價格在移動平均線下方，則處於下降趨勢。
市場調整期
有一個不十分可靠的理論是，如果價格先向一方運動，那麼真正的運動方向則相反。如果做多，止損應該放在最近的低點下方；做空，止損則應該在最近的高點上方。
• 當價格接近下通道線後折回，則做多。
如果價格下降到接近上通道線或者向下穿過MA，那麼平倉。
• 當價格從上通道線上方反轉，做空。
如果價格在接近下通道線時向上反轉，或者向上穿過MA，則平倉。
利用反轉信號來確認價格在接近上、線通道線時的反轉點；通常利用收盤價作為趨勢過濾器MA的參數；利用追蹤止損買進、止損賣出挂單來確認進出場時機。
示例 1
IBM 股價以及 7% 包絡線通道指標，30日EMA。
1. [L] 處做多——價格接近下通道線時出現鈎形反轉。
2. [X] 處平倉——價格重新收於MA下方。
3. [L2] 處做多——價格接近下通道線後向上反轉。
4. [S] 處做空——價格接近上通道線後向下反轉。
5. 持續上述交易模式直到價格突破該通道——可以通過價格突破交易區間確認，接下來轉換交易下面介紹的交易策略。
趨勢市場
當價格處於單邊運動時，它不會從通道的一側穿向通道的另一側，而是傾向於在MA的一側：上升趨勢中，位於MA的上方；下降趨勢則位於MA的下方。
• 在上升趨勢中，如果價格從上通道線下降，遇到MA後又折回，那麼做多。
當價格從上通道線下降並且向下穿過MA時，多單平倉。
• 下降趨勢中，如果價格反轉但沒有向上穿過MA便又折回時，做空。
當價格向上穿過MA時平倉。
做多時，在最近的低點設置止損；做空則在最近的高點處設置止損。
收盤價通常充當趨勢過濾器的作用。
示例 2
IBM 股價以及 12% 包絡線指標，30日EMA
1. 第一個做多信號[L4] 產生於盤整期。當第二根K線突破交易範圍後，將其視為趨勢信號，並調整百分比以適應增加的波動性。
2. [X2] 處價格沒有突破前期高點，平倉。
3. [L5] 處價格沒有擊穿MA，做多。在最近的低點下方設置止損。
4. [X3] 處價格接近上通道線後向下折回，平倉。
5. [L6] 處價格不斷超過前期高點，做多，在[X4] 處平倉。
設置
包絡線指標的默認設置是5%以及20日EMA。
Price Envelopes
Price envelopes (or percentage bands) are plotted at a set percentage above and below a moving average. They are used to indicate overbought and oversold levels and can be traded on their own or in conjunction with a momentum indicator.
The length of the moving average should be varied according to the cycle that you are trading. See Moving Averages for details.
The Percentage should be set so that about 90% of price activity is contained within the bands. Adjust the band width if volatility increases over time.
Trading Signals
First, identify whether price is trending or ranging:
• When price swings back and forth across the moving average it is ranging.
• When price stays above the moving average it is in an up-trend.
• When price stays below the moving average it is trending down.
Ranging Market
The theory is that a movement that starts at one price band is likely to carry to the other, though this is not entirely reliable. Stop losses should be placed below the most recent low when you go long or above the latest high if you go short.
• Go long when prices turn up near the lower band.
Close your position if price turns down near the upper band or if it crosses back below the moving average(from above).
• Go short when price turns down near the upper band.
Close your position if price turns up near the lower band or crosses back above the moving average (from below).
Use reversal signals to detect turning points close to the upper and lower bands.
Closing price is often used as a filter with the moving average. Trailing buy- and sell-stops can be used to time entry and exit points.
EXAMPLE 1
IBM is charted with Percentage bands at 7% around a 30 day exponential moving average.
1. Go long [L] - there is a hook reversal when price is near the lower band.
2. Exit [X] the long position when price closes back below the moving average.
3. Go long again [L2] when price turns up near the lower band.
4. Go short [S] when price turns down near the upper band.
5. Continue with this pattern until price begins to trend (indicated by the breakout from the trading range) then switch to the signals below.
Trending Market
When price is in a trend it does not cross from one band to the other, but tends to stay above the moving average in an up-trend (or below in a down-trend).
• In an up-trend: Go long when a price correction respects the moving average (price turns down from the upper band and then turns back up when still above the MA).
Close your position when price returns to the upper band or crosses to below the moving average.
• In a down-trend: Go short when a rally holds below the moving average, after price turns up from the lower band.
Exit when price returns to the lower band or crosses to above the moving average.
When going long - set stop losses below the most recent low. When going short - set them above the latest high.
Closing price is often used as a filter.
EXAMPLE 2
The above chart of IBM is continued but with Percentage bands at 12% around a 30 day exponential moving average.
1. The first long signal [L4] is generated while price is still ranging. Switch to trending signals when the next bar breaks above the trading range and adjust the percentage bands to the increased volatility.
2. Exit [X2] when price turns down (below the Low of the highest day).
3. Go long [L5] when price respects the moving average. Set a stop-loss below the recent minor low.
4. Exit [X3] when price turns down near the upper band.
5. Go long (when price exceeds the previous days High) at [L6] and exit at [X4].
Setup
See Indicator Panel for directions on how to set up Price Envelopes.
The default bands are set at 5% around a 20 day exponential moving average. To alter the default settings - Edit Indicator Settings.
本文翻譯由兄弟財經提供
文章來源：http://www.incrediblecharts.com/indicators/price_envelope.php