SDS-100 RSSI dBm calibration

[kf4lza]

Not sure if this has been posted or not, I ran my signal generator on every band through my SDS-100 and its consistently around 5 dBm stronger than what I am injecting into it (i.e. -100 dBm from signal generator = -95 dBm on scanner's display). I wish there was a service menu to calibrate the dBm reading. Has anyone did this test and found similar results?

 

[Ubbe]

Has anyone did this test and found similar results?

I have the same +5dBm readout.

SDS100 test

/Ubbe

 

[merlin]

This varies a bit with band and done with software control. The user guide should tell the sensitivity and best reading your generator output in microvolts.
Now consider you have a system gain going on here weather looking at Dbm, uV, or S units on the scanner.
At the meter, that sounds close.
The RSSI is a reflection of the signal after that gain figure.
Why they incorporate an attenuator on these newer scanners.

 

[kf4lza]

I have the same +5dBm readout.

SDS100 test

/Ubbe

So then what gives? There should be a way to calibrate then. I have attempted to change filter settings etc. with no changes noticed. Are they applying some sort of formula to the dBm reading given against a RSSI (DC analog signal conversion)?

 

[Ubbe]

The receiver chip are a microprocessor that communications using I2C where you can interrogate the chip for the signal strenght values. You then calibrate that to a RSSI table. It has to be a calibration function in the scanners service mode. Uniden where fiddling with different gain values in the preamplifier and perhaps they didn't bother, or forgot, to recalibrate the values after their latest gain change. 5dB isnt' much of an error.

/Ubbe

 

[merlin]

With an overall system gain of +5Db ypu shouldn't have to change anything. Try a 5 Db attenuator at the signal generator.

 

[kf4lza]

that makes no sense, I have a calibrated signal generator. If I inject a -80 dBm into the scanner I would expect to see somewhere around -80.5 to -81.5 dBm on the readout taking into consideration of the losses in coax and adapters. Any other amateur or commercial radio shows the correct signal. I believe the way they programmed the RSSI readout is using another algorithm. No matter what level of signal is injected (-125 dBm breaking squelch into the scanner up to -50 dBm) the SDS-100 is always showing a greater signal reading by about 5 dBm.