The laboratory offers calibration service for watchesstop watches with internal crystal and step motor . the calibration of watchesstop watches includes the measurement of its relative frequency accuracy 计时表本所为石英及机械表提供校正服务,包括测量计时表内部频率的准确度。
The calibration of a spectrum analyser normally includes checks on frequency accuracy , level flatness , level linearity , input attenuation and calibration reference output 频谱分析器的校正工作一般包括检查频率准确度、功率电平不平坦度、标度线性、输入衰减及参考输出值的校正。
The merits of dds such as super fine frequency resdutlon 、 high frequency accuracy 、 easy programmed can be in combination with the excellent character of narrow - band tracing filter merits of pll 它可以将dds的超高频率分辨率、高频率精确度、容易实现程控等优点与锁相环良好的窄带跟踪滤波特性相结合。
By making full use of favourable narrow - band tracing filter character of pll and by combining the merits of dds such as super fine frequency resolution 、 high frequency accuracy 、 very fast frequency hoping with it , the pll / pll + dds frequency synthesizer presents wide band high quality source and super small frequency hoping step . while the electronically tuned filter abates the image interference and notably improves the selectivity . the theorem of frequency synthesizer and center - frequency - fixed filter is simply but adequately introduced first in this paper 课题中所采用的pll或dds pll锁相频率合成方法充分发挥锁相环良好的窄带跟踪滤波特性,并结合dds的高频率分辨率、高频率精确度和高速频率捷变等优点,分别实现了系统所要求的高质量宽带本振源和小步长频率捷变;采用电调谐选频技术,则大大改善了接收机的选择性和抗干扰能力。
In this system two oscillator are used for mixing . pll for high local oscillator and dds + pll for low local oscillator . by making full use of favourable narrow - band tracing filter character of pll and by combining the merits of dds such as super fine frequency resolution , high frequency accuracy , very fast frequency hoping with it , the pll / pll + dds frequency synthesizer presents wide band high quality source and super small frequency hoping step 系统采用两次混频,其中高本振的设计采用pll锁相环频率合成来实现,充分发挥了锁相环频率合成器的优良特性,实现了系统所要求的高质量宽频带本振源;低本振采用pll + dds频率合成来实现,结合pll优良的锁相特性与dds的高频率分辨率、高频率精确度等优点,实现了频率的小步进高精度合成。