Si4713 FM transmitter

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hasanonurcakar
 
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Si4713 FM transmitter

Post by hasanonurcakar »

Hello everyone
I Have a Si4713 fm transmistter, and i used adafruit example codes for arduino but there is a problem. chip is not stable at 3.4 GHz, there is a signal and its power is -40 dBm. i am sure this is from transmitter.
Another problem is that When i upload same code without any change, the main signal occure sometimes 100 MHz another time 95 Mhz or anything.

What is the problem ?
Could you please help me
Thanks

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adafruit_support_mike
 
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Re: Si4713 FM transmitter

Post by adafruit_support_mike »

When the Si4713 powers up, it automatically scans the spectrum to see what channels are being used, and where it has the best chance of transmitting successfully.

A few people have run into an issue where the chip seems to find a very low-power band. The problem seems to have something to do with the antenna, because changing the length of the antenna wire has a repeatable effect on the glitch.

Try coiling the free end of the antenna to change the effective impedance and wavelength. An inch or two at a time seems to be a good increment.

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hasanonurcakar
 
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Re: Si4713 FM transmitter

Post by hasanonurcakar »

Thank you Mike for rely

But there is a misunderstand because the scanning code is not used for my project.
i try the antenna impedance issue but no improvement İ want to arrange 102.3 but i upload code there are two signals which are 3.7 GHz and power is -40 dBm and fixed other signal is not 102.3 it change sometimes 90 MHz or anything

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adafruit2
 
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Re: Si4713 FM transmitter

Post by adafruit2 »

can you post the output? i have no idea how a 3.4ghz signal could be visible.

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hasanonurcakar
 
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Re: Si4713 FM transmitter

Post by hasanonurcakar »

My signals are below.Same code but different frequency and other signal is 3.35 GHz
Attachments
My main signal
My main signal
4.jpg (148.39 KiB) Viewed 995 times
Same Code but different main signal
Same Code but different main signal
3.jpg (143.79 KiB) Viewed 995 times
My 3.35 GHz signal
My 3.35 GHz signal
20150609015917.jpg (139.06 KiB) Viewed 995 times

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adafruit2
 
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Re: Si4713 FM transmitter

Post by adafruit2 »

could be that there is harmonics at other frequencies.
you could try changing the length of the antenna.

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hasanonurcakar
 
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Re: Si4713 FM transmitter

Post by hasanonurcakar »

Of I tried change antenna length. But there is no difference. also the antenna length does not explain my problem which is same code but different frequecny.

Of course could be harmonic but we work FM frequency, and the undesired signal is 3.5 GHz and 3500 MHz / 100 MHz which is 35th harmonic. and this result is not rational. and my measurement is in RF ABSORBER so other frequencies dont affect system.

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adafruit2
 
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Re: Si4713 FM transmitter

Post by adafruit2 »

You could try contacting silabs. we just put their chip on the breakout board, it isnt programmed by us or anythign so we dont know what it could be

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