Off Topic: how would you get a signal into a radio IC without broadcasting?

[john doe]

Posted on November 04, 2017 at 20:18

I'm using my stm32f446 nucleo to build a weather band radio with SAME decoder.  If the weather is good, the only emergency alert broadcast is the required weekly test.  Debugging my code when I have only one opportunity to receive a message per week, is slow going.  I do have a .wav file of an emergency alert broadcast, and would like to somehow get it into the antenna pin of an si4707 chip, without actually broadcasting it.  Perhaps someone here knows how to go from a .wav file on a computer to the antenna pin of a radio IC.  The chip manufacturer's forum is rather inactive.  Any ideas? 

If its not appropriate to post this here, moderators, please delete it.

[Tesla DeLorean]

Posted on November 04, 2017 at 22:25

Perhaps you can find a HAM Radio guy who can put everything in a faraday cage and feed the wave/audio into his radio tuned to the appropriate frequency?

Assuming the .WAV needs to be modulated back onto the appropriate carrier.

Signal Generator with Modulation Input?

https://en.wikipedia.org/wiki/Signal_generator

 

[Tesla DeLorean]

Posted on November 04, 2017 at 22:52

Amazon has little AM transmitters from $35, more expensive ones have USB and MP3 from SDCARD. People use these for Christmas light shows and museum tours, etc.

I know you didn't want to broadcast, but this would be my approach not having an AM modulation circuit to hand, and I could probably MacGyver a faraday cage with things I could pick up at Menards/Lowes. Or use an ammo case, or wrap an amazon box with tin foil.

[Jack Peacock]

Posted on November 05, 2017 at 01:16

Basically what you are asking for is a way to turn off the carrier in the transmitter and only send the modulation to the antenna input.  The Si4707 runs at a narrow frequency range and requires an RF carrier with FM modulation, so the only way you can get your WAV file into it is through a compatible transmitter.  But I doubt a WAV would work.

The Si4707 looks for RDS packets embedded in the FM signal, so you'd need both an FM transmitter for the weather band, plus a way to encode the RDS packets (I am not an expert on this).  Not sure where you'd find something like that except for commercial transmitters, and (to be technical) you may run into problems with the FCC since the transmitter requires a license unless you ensure the field strength won't reach more than a few feet.

Messing with the weather band can be serious depending on where you live.  At work we would always test transmitters in Faraday cages if there's a risk to public service bands.  Jamming a weather band radio signal in tornado prone areas can endanger lives.

  Jack Peacock

[john doe]

Posted on November 05, 2017 at 02:13

WB SAME Status
 Status: 0x80 10000000 CTS
SAMEINTs: 0x07 00000111 SOMDET PREDET HDRRDY
 State: SAME header message complete
 Msg len: 74 bytes
 Conf: 3
 Msg:�?�?�?�?�?�?�?

thanks guys, i figured it wouldn't be as simple as I had hoped. nothing good ever is

I'll get it, it'll just take a few more weeks.

[Tesla DeLorean]

Posted on November 05, 2017 at 01:36

I think you get to set the FM station the signal is pulled from, ie just honking and tones from your local broadcaster. The signals in question, and examples on YouTube, were recorded off air. Radio Shack used to have little FM broadcasters back in the day, and now Amazon has Home Radio FM devices.

https://www.amazon.com/Adjustable-Broadcast-Transmitter-conference-christmas/dp/B07194M2Z6/ref=pd_day0_328_14?_encoding=UTF8&psc=1&refRID=7F1C6EA9XGQPQYGKPF8A

 

https://www.ebay.com/itm/FM-Transmitter-Radio-Broadcast-CZH-T200-Portable-Stereo-Power-Adjust-US-SHIP-/182527184301