IMD issues and uncalibrated mic meter.

[Kb2uka]

I9 iMac V3.10.0 essdr Sunsdr2dx

I have noticed an increase in imd with same microphone and daw levels used from previous version.

Mic db meter will not reach zero db and I am unable to tell if I am overdriving or not. I run a digital audio workstation and have my levels set in there but don't kno2 what level to set pc mic to because db meter is not accurate. This is a major fix that is needed especially for us that run rack gear/virtual rack gear into eesdr.

Thanks Doug Kb2uka

[1972igor]

ESDR3 0.10.0.Alpha Build 03112021 there is improper indicator Mic meter lower aisles the input of the transmitter ( input MIC PC ) was filed generator 1000 Hz with an input level of 0 dB , the gain control for microphone input is set to 0 dB on the gain and input level is attenuated with step minus 5 dB to the input of the transmitter , in this case we compared the indications of levels at the output of the generator and the input level of the transmitter input level 0 dB 0 dB microphone shows enter minus 5 dB MIC shows minus 2.5 dB input minus 10 dB, the microphone shows minus 5 dB enter minus 15 the microphone level, indicates a negative minus dB 7.5 dB input -20 dB shows the signal level minus 10 dB enter minus 25 dB microphone shows minus 12 dB input-30dB shows the microphone level minus 15 dB enter minus 35 dB shows the microphone level minus 17dB

[John-KC2QMA]

Here are some of my thoughts on Audio Metering in ESDR3

1. It is important to first consider the limitations /specification of the built in mic amplifier in the transceiver itself.

• What is it’s frequency response?
• What is maximum input before distortion?
• What is the input impedance?
• What is Unity Gain (input and output of pre-amplifier is at the same gain)

2. Accurate metering for audio signal in ESDR3 is critical for proper modulation.

• 0db audio signal at analog microphone input should show the same on metering in the software and be liner at various levels and liner across the mic pre-amplifier frequency range.
• Any stage of the PROC Blocks that can add audio gain or reduce audio gain should have a meter.
• Audio compressors and limiters need to have Gain reduction meter with Threshold indicator.
• There should be an output meter in the final stage of the PROC menu before it goes into the RF P.A.

3. ALC Meter / Indicator

• There should be some kind of indicator to tell the user when the transceivers RF PA is starting to go into power limiting. This will tell the user when they are over driving the RF PA causing possible IMD.
• A simple red indicator light in the PROC menu would be highly recommended.
• Can also have ALC indicator located next to the power and temperature indicators located at the bottom of ESDR3.

Possibly a Red, Green, Red ALC indicator would be effective.

• RED To Low (Under Driving the PA)
• GREEN OK (Perfect Modulation)
• RED To High (Over Driving the PA)

[Kb2uka]

Couldn't agree more, John. Thank you!