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RogerClark
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Re: Rogers postbag - FM radio band transmitter

Post by RogerClark » Wed Feb 22, 2017 9:04 pm

Vassilis

Thanks for the link to the library, but it only seems to have commands to set the frequency and not much else.

However it would be a good starting point.

@raphik

I would try to buy the module, or just buy the whole board with the display and simply cut the tracks from the mcu to the radio IC. Or possibly cut the board in half to separate the mcu from the radio part

raphik
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Re: Rogers postbag - FM radio band transmitter

Post by raphik » Wed Feb 22, 2017 10:52 pm

Well, the truth is that the QN8027 IC has few, boring programmable features: initialization, calibration, frequency and emission power. The one really interesting thing is the sending of data via RDS. RDS data packages must match a particular, given structure before being sent. Otherwise receivers wouldn't understand receipt and no message would be displayed on their screens. I'm now working on that but have still not found the right way.

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Vassilis
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Re: Rogers postbag - FM radio band transmitter

Post by Vassilis » Thu Feb 23, 2017 7:45 am

Yesterday I purchased one of those FM transmitter modules (with LCD). I like the RDS capability.

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RogerClark
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Re: Rogers postbag - FM radio band transmitter

Post by RogerClark » Thu Feb 23, 2017 8:24 am

Vassilis wrote:Yesterday I purchased one of those FM transmitter modules (with LCD). I like the RDS capability.
I don't have an RDS radio but I do have one of those TV dongles that work as SDR (Software Defined Radio), and I know some of the SDR software can display the data that is in the FM signal

I suspect that would be the easiest way to debug any RDS data.

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Re: Rogers postbag - FM radio band transmitter

Post by raphik » Thu Feb 23, 2017 8:48 am

@ RogerClark. I have also a DVB dongle RTL-SDR capable. A suitable RDS spy software is crucial for displaying miss-built RDS packages. I understand that standard receptors discard wrong packages.

@ Vassilis. Geia sou. Nice purchase! Let's know when you receive the parcel.

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Vassilis
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Re: Rogers postbag - FM radio band transmitter

Post by Vassilis » Fri Feb 24, 2017 7:43 am

raphik wrote:@ Vassilis. Geia sou. Nice purchase! Let's know when you receive the parcel.
Geia sou raphik I will let you know !

[Geia sou = Hello]

raphik
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Re: Rogers postbag - FM radio band transmitter

Post by raphik » Tue Feb 28, 2017 11:59 pm

RogerClark wrote: I don't have an RDS radio but I do have one of those TV dongles that work as SDR (Software Defined Radio), and I know some of the SDR software can display the data that is in the FM signal

I suspect that would be the easiest way to debug any RDS data.
I am displaying RDS data on my laptop using the free soft "RDS Spy" http://rdsspy.com/.
Image

Lots of data can be analyzed.
Image

As MPX signal source I am using a cheap, old fashioned handheld receiver. I am extracting MPX from the volume attenuator, through a 15K resistor and injecting it into the laptop through its microphone input.
Image

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RogerClark
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Re: Rogers postbag - FM radio band transmitter

Post by RogerClark » Wed Mar 01, 2017 7:57 pm

Is the RDS transmitted in with the audio?

I assumed it was some sort if , separate additional signal that was modulated onto the same carrier. But from what you have posted, it sounds like somehow the RDS is sent by mixing it with the audio.

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Re: Rogers postbag - FM radio band transmitter

Post by raphik » Wed Mar 01, 2017 9:48 pm

There are actually one main carrier and up to three extra subcarriers.

In the beginning FM used to be quite a simple wave. But then, FM Stereo came and a 19 KHz pilot signal and an extra subcarrier was added at 38 KHz just to carry the so named subtraction channel (L - R). Older receivers precess only frequencies under let's say 18 KHz what includes both left and right channels (L + R). Modern, stereo receivers can detect the 19 KHz pilot signal and if so they separate left and right channels just adding and subtracting both parts of the wave: (L+R) + (L-R) = 2L for the left channel, and (L+R) - (L-R) = 2R for the right one. When RDS appeared into scene, a new subcarrier at 57 KHz was added. Nowadays an FM wave is a multiplex wave (MPX).
Image

In 1997 a new standard called DARC (DAta Radio Channel) was introduced in Europe. It is used in Munich to transmit public transport data in bus an tram stations.
Image
https://apollo.open-resource.org/missio ... -on-90-mhz

That said, one important thing to know is that MPX is present in cheap FM receivers at the input of theirs volume attenuators. As audio amplifiers do not process frequencies beyond 18 KHz, the RDS subcarrier doens't reach the headphones output. That's why I'm extracting it from the attenuator through a 15 KOhm resistor.

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Re: Rogers postbag - FM radio band transmitter

Post by zmemw16 » Wed Mar 01, 2017 10:08 pm

tell me that is an orange wire and i might believe 15k, however it looks like a 1k5
srp

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