Fluctuations in the $ETH /BTC exchange rate have a significant impact on investors’ decisions because it reflects changes in the value of Ethereum relative to Bitcoin. If the $ETH /BTC exchange rate rises, it means that Ethereum has increased in value relative to Bitcoin, and vice versa, it means that it has depreciated. This could impact investor interest in Ethereum, as it could indicate that Ethereum's fundamentals are becoming more attractive relative to Bitcoin, or that the market expects Ethereum to outperform Bitcoin in the future.

Technical analysis can provide insights into the $ETH /BTC exchange rate trend and help predict market trends. Investors often use technical indicators such as the relative strength index (RSI) and the moving average convergence divergence indicator (MACD) to predict market movements. For example, an RSI above 70 usually indicates that the market may be overbought, while an RSI below 30 may indicate that the market is oversold. The MACD indicator reveals changes in market momentum by showing the relationship between two moving averages, with intersections often considered to be buy or sell signals.

Using these technical analysis tools, investors can better understand the fluctuations in the ETH/BTC exchange rate and make more informed investment decisions accordingly. However, it should be noted that technical analysis is not omnipotent, and other factors such as market sentiment, news events, and changes in market supply and demand will also affect exchange rate trends.

As for when to buy Ethereum, if the ETH/BTC exchange rate is at support and positive technical indicators are emerging, such as the oversold territory of the RSI and the bullish crossover of the MACD, this may be a time to consider buying. However, investors should consider market analysis, personal risk tolerance and investment objectives before making investment decisions.