Add 10dB pad when measuring RF Tx power

[stephen168]

I observed that people always add a 10 dB pad when they measure the Tx power from the device. Apart from avoid to damage the equipment, is there any other purpose?

 

[VEBill]

A 10dB pad ensures (in theory) at least a 20dB return loss; in other words, a very good match. This can help to ensure that the source is loaded correctly and measurements are accurate.

There are other possible explanations (e.g. range of instrument), but this is the more common reason.

 

[Higgler]

I agree. It adds some accuracy for measuring output power into a well matched component.

If the amp providing the power has a bad output match and the component it's connected to has a bad match (like an ugly antenna), this method can give very wrong results as to the actual power out the antenna due to energy bouncing back and forth. i.e. it can be off by 10 dB or more when doing an antenna power radiation test.