本論文的主要目的為發展電離層短波使用的最高可用頻率以及電場強度的預測模式，進行越地平通訊(Over-The-Horizon Communication)時，可以擁有較穩定，並且有保密的傳遞訊息，不需要經由商業衛星傳播；高頻電波具有低成本的發射接收儀器，低發射功率且足夠強的電場強度。意指當海船在海上，或是人員在陸上，欲與陸上另一端通訊時，事先評估通訊的準確度，進而提供可靠穩定的通訊品質。高頻電波電場強度之預測有下列幾項步驟，第一：預測太陽黑子數，使用McNish-Lincole 法來對未來的太陽黑子數做預測，與NOAA 比較，吾人所預測的較為接近真實的太陽黑子數；第二：預測電離層F2 層的臨界頻率，參考IRI 模式發展F2 層臨界頻率的預測方法，結果發現在Kp<3 時，大多數的預測誤差都小於20%；第三：計算出最大可用頻率，使用物理特性推算出當地上空與距離4000公里的最大可用頻率，再使用經驗式，將某特定接收距離的最大可用頻率算出； 第四：預測通訊電場強度，經過以上的步驟，再計算高頻電波在通過此通道時，電波在空間傳播時會產生的衰減，經由ITU 所提供的經驗式，推算出如反射高度、角度等等。此預測模式的優點在於任何的兩地皆可以使用此模式預測，沒有地界的限制，但由於系統的衰減也是重點之一，系統特性眾多無法一一分析，因此還不能算是為一個完整模式，但相信可以提供爾後的人開啟先河之流。

The main objective of this thesis is developing the prediction of maximum usable frequencies and field strengths in the ionosphere on the HF band. Using Over-The-Horizon communication, we have the stable and secret information and do not broadcast by commercial satellites. It has low cost of terminal equipment, low power requirements and adequate signal strengths on the HF band. To communicate with the receiver, It provide the reliable quality of communication that estimate the accuracy of the broadcast.
There are four steps of the field strengths prediction on the HF band. First, to use McNish-Lincole method predicts the smoothed sunspot numbers. Comparing with the NOAA prediction, ours are close to the observation of smoothed sunspot numbers. Second, the forecast of the critical frequencies in the F2 layer of the ionosphere refers to the prediction method of the I.R.I. model. When the Kp value is smaller than three, the major prediction error is lower than 20%. Third, compute the maximum usable frequencies on the HF band. According to 0 and 4000 km of the maximum usable frequencies, we estimate the receiver distance of the maximum usable frequency by the experience formulas. Fourth, we get the forecast of field strength. Propagating the tunnel in the ionosphere, we compute the total loss on the HF band. The advantage of this prediction model is to communicate with anywhere, but the system loss is an important point. It is not a complete prediction model, because the properties of systems are different. Believe it that this is a piece of the knowledge on HF band for the researchers.

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