价格包络线（或称百分比通道）是按照固定百分比设置在移动平均线上方和下方的两条通道线。它们可以单独显示超买、超卖水平，也可以与动能指标结合起来使用。移动平均线可以根据所交易周期设置，百分比的大小应该将90%的价格波动包含在通道内为宜。如果价格波动随着时间的推移变得剧烈，则应适时调整通道线的百分比。
交易信号
首先，确认价格是处于趋势中还是调整期：
• 如果价格在移动平均线周围波动，则说明处于调整期。
• 价格在移动平均线上方运动，则处于上升期。
• 价格在移动平均线下方，则处于下降趋势。
市场调整期
有一个不十分可靠的理论是，如果价格先向一方运动，那么真正的运动方向则相反。如果做多，止损应该放在最近的低点下方；做空，止损则应该在最近的高点上方。
• 当价格接近下通道线后折回，则做多。
如果价格下降到接近上通道线或者向下穿过MA，那么平仓。
• 当价格从上通道线上方反转，做空。
如果价格在接近下通道线时向上反转，或者向上穿过MA，则平仓。
利用反转信号来确认价格在接近上、线通道线时的反转点；通常利用收盘价作为趋势过滤器MA的参数；利用追踪止损买进、止损卖出挂单来确认进出场时机。
示例 1
IBM 股价以及 7% 包络线通道指标，30日EMA。
1. [L] 处做多——价格接近下通道线时出现钩形反转。
2. [X] 处平仓——价格重新收于MA下方。
3. [L2] 处做多——价格接近下通道线后向上反转。
4. [S] 处做空——价格接近上通道线后向下反转。
5. 持续上述交易模式直到价格突破该通道——可以通过价格突破交易区间确认，接下来转换交易下面介绍的交易策略。
趋势市场
当价格处于单边运动时，它不会从通道的一侧穿向通道的另一侧，而是倾向于在MA的一侧：上升趋势中，位于MA的上方；下降趋势则位于MA的下方。
• 在上升趋势中，如果价格从上通道线下降，遇到MA后又折回，那么做多。
当价格从上通道线下降并且向下穿过MA时，多单平仓。
• 下降趋势中，如果价格反转但没有向上穿过MA便又折回时，做空。
当价格向上穿过MA时平仓。
做多时，在最近的低点设置止损；做空则在最近的高点处设置止损。
收盘价通常充当趋势过滤器的作用。
示例 2
IBM 股价以及 12% 包络线指标，30日EMA
1. 第一个做多信号[L4] 产生于盘整期。当第二根K线突破交易范围后，将其视为趋势信号，并调整百分比以适应增加的波动性。
2. [X2] 处价格没有突破前期高点，平仓。
3. [L5] 处价格没有击穿MA，做多。在最近的低点下方设置止损。
4. [X3] 处价格接近上通道线后向下折回，平仓。
5. [L6] 处价格不断超过前期高点，做多，在[X4] 处平仓。
设置
包络线指标的默认设置是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.
本文翻译由兄弟财经提供
文章来源：http://www.incrediblecharts.com/indicators/price_envelope.php