Need more resolution when testing at low power

For users of 1830A DC Substitution RF Power Meter
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abrush1
Posts: 56
Joined: Fri Feb 29, 2008 2:13 pm
Real Name: Andy Brush

Need more resolution when testing at low power

Post by abrush1 »

Here's the situation:

You put an attenuator between the DUT port of your feed-through standard. Since you have measured the S-parameters of the attenuator, you calculate a new calibration factor for the assembled feed-thru+attenuator. With a 20 dB attenuator, the calibration factor is approximately 100, and the front panel reads the output power correctly.

The problem is that the front panel and the bus command, “GET powsubk_1 CV“ both display in the format of d.dddd mW, so when the output power is 0.01 mW, there is about 0.5% potential rounding error.

Solution for the display:

Auto Scale Reading (Read/Write)
Located SETUP—Instrument—Auto Scale Reading menu. This control is defaulted to False, all power reading will be displayed in mW. Setting this control to true will show power reading in scaled notation from nW to kW. Control is available in firmware version 1.1.28a and greater. (From Rev. G of the Manual)

Solution for automation using serial or IP bus commands:

use the command "GET powsubk_1 RAW", which returns the un-scaled value (Watts) in machine precision of the 1830A, which is about 20 digits. (This is NOT documented in the 1830A manual revision G, but has long been a feature of the 1830A) It is illustrated in example #1 of, viewtopic.php?f=5&t=64

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