源衰减器的功率输出精度

当衰减器改变时，衰减器偏移被补偿，但仅有一个固定的偏移数（例如，对于10dB的变化恰好为10dB），但衰减器具有一些非理想的行为，并且可能具有9.75或10.25dB的损耗。
这是源功率中的错误。
两种解决方法：1）使用开环模式，它可以提供70 dB的范围（将低端向下降30 dB，因此你可以从低于-60 dB到达+ 10 dB左右）
）。
2）使用call-all校准多个通道，每个通道具有不同的衰减器值。
然后使用通道测量您想要的功率。



     以下为原文

  The attenuator offset is compensated when the attenuator is changed but only with a single, fixed offset number (e.g. exactly 10 dB for a 10 dB change) but the attenuators have some non-ideal behavior and might have 9.75 or 10.25 dB of loss.  This is an error in the source power.

Two work-arounds:
1) use open loop mode, which gives you 70 dB of range (drops the low end down by an additional 30 dB, so you can go from -60 dB below the attenutor value to +10 dB or so above).

2) use call-all to calibrate several channels, each with a different attenuator value. Then use the channel for the measurement of power that you want to make.

最简洁的答案是不。
它与源衰减器的位置有关（见下图）。
衰减器位于参考接收器之后，因此参考接收器无法看到新衰减器设置下的路径损耗的任何变化，因此即使您打开接收器调平，源功率电平也不会得到非常精确的补偿。
当接通时，衰减器偏移偏好对衰减器设置的标称损耗进行粗略补偿，但不补偿新衰减器路径的频率响应。
作为一般规则，当您关注精确的功率设置和/或读数时，不应将源衰减器保持在自动模式。
PNA-X具有较大的ALC范围（在大多数频率下约为40 dB），您应该选择一个衰减器设置，以最大化测量的可用ALC范围。
一旦确定了这一点，就可以手动放置衰减器，执行导向功率校准，然后使用ALC系列来改变功率。
打开接收器调平后，将测量并补偿源线性度的任何不准确性。
您还可以使用开环模式（对于端口1和3）获得比典型40 dB更大的功率范围。
当然，对于Open Loop，我们强烈建议您使用接收器调平。
如果激励设备所需的功率范围仅大于使用ALC或开环的单通道所能达到的功率范围，则可以使用不同的源衰减器设置设置多个通道，然后使用Cal All校准它们。
Cal All例程将执行单个合并功率传感器校准，但会针对不同的衰减器设置更正每个通道。
！HTTPS：//dl.dropboxusercontent.com/u/87949221/Forum/ThredID_115912/SrcAttenuatorLocation.png！



     以下为原文

  the short answer is no.  it has to do with the location of the source attenuator (see picture below).  the attenuator is after the reference receiver and therefore any changes to the path loss at a new attenuator setting is not seen by the reference receiver and therefore even if you have receiver leveling turned on, the source power level will not be very accurately compensated for.  the attenuator offset preference, when turned on, does a rough compensation for the nominal loss of the attenuator setting, but the frequency response of the new attenuator path is not compensated for.  

As a general rule when you are concerned with accurate power setting and/or reading, you should not leave the source attenuator in Auto mode.  The PNA-X has a large ALC range (about 40 dB at most frequencies) and you should pick an attenuator setting that maximizes the usable ALC range for your measurement.  once you have established that, then you put the attenuators in manual, perform your guided power calibration and then you can use the ALC range to change the power.  with receiver leveling turned on, any inaccuracies in the source linearity will be measured and compensated for.  You can also use the Open Loop mode (for port 1 and 3) to get even a larger power range than the typical 40 dB.  of course with Open Loop, we highly recommend that you use receiver leveling.  

If the power range that you require to stimulate your device with is simply larger than what you can achieve in a single channel with ALC or open loop, then you can setup multiple channels with different source attenuator settings and then use Cal All to calibrate them.  the Cal All routine will do a single consolidated power sensor calibration, but will correct each channel for the different attenuator settings.

!https://dl.dropboxusercontent.com/u/87949221/Forum/ThredID_115912/SrcAttenuatorLocation.png!