Stereo Tool

Alright! I am now trying to calibrate it. I am having trouble trying to calibrate it.
When I used the volume test at 10240 tone, I increased the volume to about 71khz (using the measurement from other stations). I went to the volume test at 20 tone, it is lower khz than the 10240 tone. I am assuming that it isn't right to increase the volume?

Also, this also is confusing. Shouldn't there be one line in the spectrum analyzer like shown on stereo tool while doing the volume test?
This was me doing a volume test on 10240 hz


This is so much pain.

Yea, should be only one 10240 tone. Now i don't know why is that happening. Are you sure you are using pure MPX input and everything on transmitter is disabled?

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control point
control point2

Yep, I had that same question too. There are options on the FM transmitter like decreasing treble and bass, Compressor ratio, threshold, attack, and release. I have treble and bass set to not add. The compressor only works with a Stereo encoder which I do not have plugged into the FM transmitter. Plus, I have the compressor threshold set to 0.0db if that even does anything. I have no clue if it does anything.
Here is the "manual" if you want to look into it. https://www.pcs-electronics.com/softwar ... 015_en.pdf
I've read it so many times. My brain is going to go crazy looking at it again.
This is just so stupid.
CompaNY proVided nO sUpporT this iS gReAT

Thanks for trying to help

From what i can see that MPX input is somewhat not good, and you need to physically skip whole that StereoEncoder part. So, you should somehow Disconnect that yellow path they call "Maxlink2" connect your MPX to that path to FM Exciter.


Thing is idk you can easily do that. and shure it will remove any warranty.

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control point
control point2

I use the MAXLINK II cable to connect audio to the FM transmitter since I am using an "MPX Input board"
Maybe the MAXLINK II doesn't have a good link to the FM Transmitter?

I just started randomly testing inputs on the FM Transmitter since I have 3 Inputs MPX USB, MPX BNC Input, MPX RCA Input. All of them use the MAXLINK II to the FM Transmitter for audio.

I figured out the "USB audio" on the FM Transmitter even though shows up as 192Khz... it isn't 192khz as it cuts off RDS, L+R

I always end up with really something like this:

Literally, I am only sending a stereo pilot! looks like I have 3 of them! It looks even in the same spots as L+R and RDS....

I tried just mono and mono isn't even good either... Oh my lord.

I opened the board out of the case (Which is another part of this whole story...)
There is an "Audio Input" connection on the FM transmitter that doesn't use MAXLINK II cable crap.
I don't know fully how I would easily use it since it is a 2-pin header.

Edited: Figured out kind of the way of fixing it... the "reference frequency" on the FM transmitter...



I got lines now in different locations... If I turn the reference frequency around it moves them...
The stereo pilot looks more proper now...

Yep doing that it's not even in the middle... so... Oh my lord.

That ref freq should be just for fine tuning output freq and should have nothing with MPX inputs.

Do not touch unless you understand what this is. Lets you fine-tune the reference frequency. You can use this
trimmer to set the frequency to exactly 100.000KHz if it’s slightly off (for example if frequency meter shows
100.002KHz).

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control point
control point2

Ah alright. The input on the FM transmitter.. is just broken...
I would assume if I tried contacting the FM transmitter CEO or whatever that, they wouldn't do anything. I mean I am stomped.

This all looks thoroughly broken. What do you see if you don't feed any signal at all? So pure silence, no stereo pilot. I'm interested in that last graph.

To test modulation levels, try the sine wave generator in Stereo Tool and try some frequencies from 30 Hz up to 60 kHz, and check if the measured levels are the same. They should be. If there are any weird filters still active, you should see them if you do this. It's hard to determine what's going on with the 19 kHz tone because if the transmitter is doing something with stereo or RDS, one would expect spikes at 38 and 57 kHz - so I'm curious what happens with those spikes if you feed a somewhat different frequency, for example 20 kHz.
If they are still there you're seeing some form of harmonics distortion, and that's going to be extremely hard to get rid of. If you don't, there might still be something running inside the transmitter that attempts to create a stereo pilot.

Oops! My bad for the late reply. I thought this thread has died.

This is what it looks like with no stereo pilot:



I don't know what that little line is on the left... Then again, I did mess with the reference frequency so the little line could be in the wrong location.
The signal is not exactly in the frequency of broadcast on the RTLSDR. So I'd assume I change the reference frequency to its at the frequency of broadcast.
I tried comparing the RF FTT FM boadcast of the transmitter to an commercial FM station with no audio, only stereo pilot and RDS. It looks a little different..

Either way: I don't think the transmitter is creating its own stereo pilot. I would assume the transmitter just has repeated frequencies... I am clueless about what is "normal" for this FM transmitter oh my god. I wish I was an FM Transmitter expert.

Well, there definitely is a filter because if I try a sine wave at 30khz up to 60khz, I end up with different levels of modulation. Half of it is lower, and half of it is higher....

I mean seriously, if I use a square wave at 30khz its a mess:

Though, due to overshoots... I mean, it goes off the frequency bandwidth....

EDIT: It's annoying to think about but basically, I got scammed by PCS electronics. They advertise a good signal off of their FM transmitter but I get crap.

That is 30 kHz??? Not 30 Hz??? 30 kHz square wave is a sine wave anyway (the sound card doesn't go high enough). And that high frequency stuff is the actual audio I assume??

It could be that very loud 30-60 kHz tones confuse the SDR, to rule that out, try lowering the level.