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This work investigates the evaluation performance of detection system for Frequency Hopping (FH) signals based on Fast Fourier Transform (FFT) with proposed decision circuit based on Adaptive Threshold Level (ATL), where the threshold level changes its value automatically without manual intervention depending on the estimated values of (SNR) in the channel, the level will be high when the noise is high and vice versus. A comparison in evaluation performance were made with a conventional mode where the decision circuit based on Manually Change Threshold Level (MCTL) done by the detector according to its observation on sensing the Signal to Noise Ratio (SNR). The results shows that the proposed mode (adaptive) is give best results for probability of detection PD and probability of false alarm PF comparing with the (Manually Change). Also the results of (adaptive) are compared with that theoretical computation and gives a very small error for high noise while vanish for low noise. Keyword: Frequency Hopping, Adaptive Threshold Level, Manually Change Threshold Level ءادأ نيسحت ايتاذ فيكتم ةبتع ىوتسم مادختساب يددرتلا زفقلا ةراشإ فشك ةموظنم رامع يمحلا دبع د رضخ دعاسم سردم تابساحلا ةسدنه مسق / ةسدنهلا ةيلك / لصوملا ةعماج ةصلاخلا لوانتي ثحبلا اذه مييقت ةسارد ءادأ ةموظنم فشك ةراشإ يددرتلا زفقلا يف ةدمتعملا ساسأ اـهلمع يوحت ةقيرط ىلع عيرسلا ريروف ل ة FFT ذاختا ةرئادب ةعوبتملاو حرتقم رارق ة رـييغت ىـلع لـمعت ةـميقل رمتـسملا يتاذـلا نيـمختلل اقفو كلذو ملتسملا لخدت نود نم يئاقلت لكشب ةبتعلا ىوتسم ءاـضوضلا ةـميق عاـفتراب ىوتـسملا عـفتري ثيح ةانقلا ببسب ةراشلإا ىلع ةفاضملا ءاضوضلا اهضافخناب ضفخنيو . دقل ت مييقتو صحف م لأا ءاد عم ةنراقم جذومن يديلقت رارـقلا ذاختا ةرئاد نوكت تاذ هيف اعبت ملتسملا لبق نم ايودي هرييغت بجي ةبتع ىوتسم سـسحت نع هتاظحلامل ـ ميق رـيغت ة ةانقلا يف ءاضوضلا . جئاتنلا للاخ نم ةيلمعلا نيبت أ ن جذومنلا حرتقملا لولأا ) رييغتلا يتاذ ( لـضفأ نم يناثلا ) ي رييغتلا يود ( نم ثيح فشكلا ةيلامتحا PD لا ةيلامتحاو هيبنت بذاكلا PF . ةنراقم مت امك ادج طيسب قرفلا ناكو ةيرظنلا جئاتنلا عم حرتقملا جذومنلا جئاتن ىشلاتيو ةيلاع ءاضوض ةميق دنع ءاضوضلا دنع قرفلا ضفخنملا ة . Received 19/5/2009 Accepted 14/2/2010 Al-Rafidain Engineering Vol.18 No.5 October 2010

Enhanced Performance of FH Detection System Using Adaptive Threshold Level