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Polar Modulation Stereo System
https://forums.stereotool.com/viewtopic.php?f=16&t=6233		 Page 3 of 5
Author:  hvz [ Sat Jan 23, 2016 4:03 pm ]
Post subject:  Re: Polar Modulation Stereo System
I have Googled a bit, according to this site the normal 19/38 kHz is used increasingly in the OIRT Band - are you sure that this 31.25 kHz is really needed?
http://ukradio.info/OIRT_Tuner/
Author:  radio700 [ Sat Jan 23, 2016 6:51 pm ]
Post subject:  Re: Polar Modulation Stereo System
in September 2015 I monitored stations in Belarus in the low FM band. All were either polar stereo or mono. After talking to a collegue why Mono he told me due to the lack of available transmission hardware. 19 kHz is mostly useless because the radios (except for some Tecsun 64-108 Tuners) decode stereo only in Polar Mode in the lower FM part.

As for the 14dB reduction: This is only for the pilot of 31,25 kHz to save deviation. The rest of the modulated Stereosignal stays at it is.
Author:  hvz [ Sun Jan 24, 2016 1:25 am ]
Post subject:  Re: Polar Modulation Stereo System
Now things are starting to make sense. Usually you generate a stereo signal around 38 kHz with no (remains of a) carrier at all. However in this 31.25 kHz modulation you do leave a bit of carrier there, so you suppress it, but not completely. And that formula might be how to do that.

Unfortunately, I still have to implement it to make the phase correct.
Author:  hvz [ Mon Jan 25, 2016 8:57 am ]
Post subject:  Re: Polar Modulation Stereo System
Yup. If you fill in 0 for f (frequency), then the formula results in 1/5 which is 13.98 dB reduction, which matches the 14 dB mentioned. So indeed this formula somehow describes a filter.
Author:  radio700 [ Mon Jan 25, 2016 2:39 pm ]
Post subject:  Re: Polar Modulation Stereo System
I think it desribes the Notchfilter of the Carrier and affects also the audio.
This is the curve from 0 to 15 kHz.
Attachment:
Curve.png
Curve.png [ 9.65 KiB | Viewed 7127 times ]
I hope I can do my tests next days, was very busy on the weekend. We should see it by doing a sweep that when the carrier is not reduced to that formula, that the audio isn't linear anymore but over attenuated in the bass. A bit like RIAA on vinyl....

In the Receiver the Carrier is amplified again by 14dB, so it will be linear again.

Attachments:
Curve.png
Curve.png [ 9.65 KiB | Viewed 7127 times ]
Author:  hvz [ Mon Jan 25, 2016 3:46 pm ]
Post subject:  Re: Polar Modulation Stereo System
Yes. So please try that, and also if it sounds "kinda" ok. If so I can try to add this function. When I figure out how to interpret it (those shapes look a lot like what I had expected, where did you find them?)
Author:  radio700 [ Mon Jan 25, 2016 4:33 pm ]
Post subject:  Re: Polar Modulation Stereo System
I made an Excelsheet and put values from 0 to 15 in 0,1 kHz Steps into the formula for "f". I don't know what j means, I just ignored it :D
Author:  hvz [ Tue Jan 26, 2016 4:47 pm ]
Post subject:  Re: Polar Modulation Stereo System
Btw according to the text, f is in kHz, so the graph would end around 15 or 16! Ugh...

I wanted to continue with this but now I really want to wait for your test results again :)
Author:  \_/ [ Tue Jan 26, 2016 5:25 pm ]
Post subject:  Re: Polar Modulation Stereo System
Quote:
[...] I don't know what j means, I just ignored it :D
j = i = sqrt(-1)
Author:  hvz [ Thu Feb 04, 2016 3:36 pm ]
Post subject:  Re: Polar Modulation Stereo System
@radio700, any progress on this?
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