HP 8714 Frac N模块问题

低于约150MHz的8714网络分析仪的用户将难以处理频率的不稳定性和模块的最终故障。
这是因为VCO控制线上使用了钽电容，工作电压范围约为-5.5至+8V。
高于约150MHz的电容总是正确偏置，但低于此，钽的偏置反转，最终失败。
*这是一个设计错误。*解决方案是更换陶瓷类型的电容器。
我会给出电路和部件号引用，但HP / Agilent不会将服务信息发布到此级别。
在模拟总线菜单节点上是A3 Frac-N组件节点18 - VCO电压驱动。
如果它测量任何负面的东西，你将遇到麻烦（最终）。
幸运的是，目前大多数RF工作都在150MHz以上，VCO电压变为正值。



     以下为原文

  Users of the 8714 network analyser below about 150MHz will have difficulty with instability of frequency and eventual failure of module. This is due to a Tantalum capacitor being used on a VCO control line that operates over about -5.5 to +8V volt range. Above about 150MHz capacitor is always biased correctly, but below this the bias is reverse for the Tantalum which eventually fails. *This is a design fault.*
Solution is to replace capacitor with ceramic type.
I would give circuit and part number references except HP/Agilent don't publish service info to this level. On Analog Bus menu node is A3  Frac-N Assembly node 18 - VCO Voltage Drive.  
If it measures anything negative you will have trouble (eventually).
Fortunately most RF work these days is above 150MHz where the VCO voltage becomes positive.