FM MPX out and FM modulation measurement

[Sparktstic]

Hi guys,

Couple of suggestions..

1/

Would it be possible to enable MPX output from the soundcard when in FMB mode?

Obviously, you would need a 196KHz soundcard to reproduce the MPX signal.

I work in Broadcasting and being able to feed an mpx signal from an FM off air signal or STL into a transmitter would be fantastic for emergency communications (temporarily replacing a faulty analogue STL receiver etc).

MPX out could also be fed to stereo modulation monitors for testing/analysis purposes.

2/

Please, please please... FM modulation / deviation measurement. Particularly for FMB purposes.

Deviation histogram over time and seperate pilot tone deviation would be amazing

[Simon G4ELI]

All notes, 2) is *very* interesting.

[m3ghe]

Used to do '1/' years back by stripping all of the de-emphasis components out of a band II tuner.

[DaveB]

Used to do '1/' years back by stripping all of the de-emphasis components out of a band II tuner.

I just tapped the audio signal from my Sony ST-311 tuners frome the appropriate pins of the chip before it went through the de-emphasis and used the signal to feed RDSSpy for RDS decoding.

A 16-bit 192kHz 2ch audio signal could be used to feed RDSSpy for RDS decoding - which might give a very small improvement over the excellent in-built decoder in SDR-Console on some signals.

[m3ghe]

Used to do '1/' years back by stripping all of the de-emphasis components out of a band II tuner.

I am talking about 36 years ago.

[Simon G4ELI]

Hi guys,

Couple of suggestions..

1/

Would it be possible to enable MPX output from the soundcard when in FMB mode?

Obviously, you would need a 196KHz soundcard to reproduce the MPX signal.

I work in Broadcasting and being able to feed an mpx signal from an FM off air signal or STL into a transmitter would be fantastic for emergency communications (temporarily replacing a faulty analogue STL receiver etc).

MPX out could also be fed to stereo modulation monitors for testing/analysis purposes.

So, we're talking 192kHz, single channel? I am now in the right frame of mind to add this an an Extra, the output will be created for the currently active RX frequency, so if you have three RXs in action then the output will switch as you change RX selection.

With this approach you can listen with SDR Console as normal and feed to RDS Spy or whatever.

[G0OFE]

That should work well.

Think it might need just a normal 192khz stereo channel..

If you just send out a 192khz unfiltered audio output from the demodulator (as HDSDR does, for example) to a specified VAC, that would do it.

One word of caution.. make sure you have a later version of VAC. I had issues getting an earlier (4.16) version to work, but once I updated, it was fine.
VBCable Hifi ( https://vb-audio.com/Cable/#DownloadASIOBridge ) is also good, and is free.

[Simon G4ELI]

That should work well.

Think it might need just a normal 192khz stereo channel..

If you just send out a 192khz unfiltered audio output from the demodulator (as HDSDR does, for example) to a specified VAC, that would do it.

One word of caution.. make sure you have a later version of VAC. I had issues getting an earlier (4.16) version to work, but once I updated, it was fine.
VBCable Hifi ( https://vb-audio.com/Cable/#DownloadASIOBridge ) is also good, and is free.

Well I don't see the point in stereo - this is the same signal as shown here, it's before demodulating. Mono 192kHz will be fine I believe.

[Simon G4ELI]

Assuming I get this going, which programs want this 192kHz via VAC?

I'll need to test...

[G0OFE]

Well I don't see the point in stereo - this is the same signal as shown here, it's before demodulating. Mono 192kHz will be fine I believe.

Had it confirmed that mono is fine.

Assuming I get this going, which programs want this 192kHz via VAC?

RDS Spy - https://rdsspy.com