Stereo Tool

Hello Everyone,

We use a 2.5 kW RVR radio transmitter. Yesterday I ran MPXTool near the transmitter.

I would like to mention a few problems that I could detect.

1- Pilot and RDS signal fluctuates a lot. (Pilot set to 9% and RDS to 4.3%)

2- I set the Test signal from MicroMPX to 1000 Hz. I set the modulation to 100 on the potentiometer on the back of the transmitter, using the MPXTool as a reference.

Then I switched to 30 Hz Square signal (I also tried 15 and 10 Hz signals). The modulation started showing around 120-140. However, I could not reduce it to 100 in the Tilt Correction section.

What can I do about these issues?



MicroMPX Output: -2 dB
MPX Power Limit: +8.0 dBr
Final Clip Drice: +0.75 dB

You doing something wrong.
- You really need clean signal in MpxTool. So somewhere around 36 and up. Sometimes you need to move around tx site, RF can make some strange interferences.
- For Pilot and RDS fluctating, i dont know why, but it's not ST, so something other is wrong. Is transmitter MPX input "clean"? What is soundcard?.. etc..
- Did you try to calibrate FM? I/O >Soundcards > FM output > Calibration? Idk even is it that there in uMPX decoder, but should be Tilt and HF calibration.

This is how it should measure when everything is fine. Monitoritng from 2.5KM away from TX, 1kW transmitter (It's intentionally tuned to 73kHz)
https://we.tl/t-bHzurSoOzj

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control point
control point2

Thank you for your messages.

We are using a Behringer UMC202HD sound card.
This evening I will go to the mountain where the transmitter is and test it again with the correct signal level.

FM output > Calibration (I don't know how to set it up.)

Also, what should be the value in the Peak Response Time and Unit tabs in MPXTool?

I tested from inside the car, 200 meters away from the transmitter tower.

MPX scope looks fine, but you see noise jumping around pilot and rds, that's not good. That's why your pilot/rds level jumping. It can be that soundcard stutters somehow.

For "peek responce time" i usually use 125us or "instant"

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control point
control point2

Thank you for your message.

Which sound card would you recommend?

We are currently using behringer UMC202HD. I also have a spare sound card as a CM6631A 192Khz DAC.

That can happen when output buffer is low, so i would first try to rise buffer a bit. I hope there is some sort of soundcard sync in µMPX, i honestly forgot and i don't use it.
Then i would run ST standalone directly form that PC to see is µMPX causing that.
That will tell you what next to do.

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control point
control point2

Assuming you are using an SDR-dongle with MPXTool, I recognize that exact behaviour! Certainly it is a problem/bug with MPXTool in the first place and not with your TX-signal. It found that it occurs especially when running MPXTool on a computer running other CPU-intensive tasks and/or using other USB devices simultaneously. You could confirm by tuning in on any other (strong) signal to see if it happens there as well.
If so, please try running MPXTool on a fast computer, and avoid using other applications and USB devices at the same time.

Good luck!

P.S. Looks like either your TX-frequency is a bit off-center, or you need to give your SDR-dongle some ppm offset in MPXTool.