TX peak power detector application

System Development
1

Hail,
I am considering an application for the limeSDR-USB that requires setting the TX power to an absolute level as the frequency
is hopped or incrementally stepped over a wide band. This isn’t a lab grade instrument requirement but requires

  1. knowing the power to within +/- 1 dB,
  2. into a 50 Ohm load,
  3. 400 to 1300 MHz,
  4. at least spanning a 20 dB power range somewhere between -30 dB minimum and 0 dBm maximum at a known point in the system that, once calibrated with a standard, does not change,
  5. a single tone,
  6. corrected using the LMS internal temperature and Lime board sensors over a range of 15 C to 30 C,
  7. initial calibration to a standard done with a lab grade RF power meter.

My first shot plan is to calibrate the TX output at maximum output over temperature and frequency and then follow up with a linearity check of the TX gain control. However, I note that the LMS7002M has a peak power detector and I am curious as to whether this would be helpful in monitoring the TX output (again assuming a 50 Ohm termination). I could not find much documentation on use of this detector beyond it’s 8 bit register setting (MEASR_PDET1_VAL[7:0]) in the “Programming and Calibration Guide” and it’s appearance in the LMS7002M features document (Figure 1: Functional block diagram). So, my queries are whether anyone has used this detector for this purpose and what the intended application of this detector is?

Rick

2

Documents found on https://limemicro.com/technology/lms7002m/
contain information on the peak power detector which should provide a good start in learning more about it. First off, I would like to understand what is represented by this quantity:
MEASR_PDET2_VAL[7:0]: Stores the value of Channel B analogue peak detector (in
active TX path) (Read only)

3

Tagging @Zack.