Does anyone know of an IC that receives around 160, 450 or 900 MHz, FM, outputs audio and is controlled by I2C, SPI or basic serial?
Silicon Labs Product Selector Tables list the Tx and Rx chips and their covered bands.
Several include the bands you mentioned.
The si4736 does weather band (162.4MHz), FM demodulation to analog audio, and is digitally controlled.
The Silicon Labs Product Selector Tables is for data links, I'm looking for a receiver that outputs audio.
I'm looking one that specifically receives 160.0 - 161.5 MHz (Railroad).
So, the follow up question is:
Can one set the SI4736 to use its External Clock source and intentionally "mis-tune" the clock to shift the Weather Band receiver to the Railroad frequency?
Since the WB has an AFC module, does this help or hurt in tuning a RR transmission?
Is this a personal, for fun project?
Well, there may be a bit more to it than that. The WB has 7 channels. According to all-knowing WikiPedia:
Frequency Old New
162.4 MHz WX 2 WX 1
162.425 MHz WX 4 WX 2
162.45 MHz WX 5 WX 3
162.475 MHz WX 3 WX 4
162.5 MHz WX 6 WX 5
162.525 MHz WX 7 WX 6
162.55 MHz WX 1 WX 7
This channel spacing of 25KHz is relatively wide.
This site lists RR frequencies http://trainweb.com/radio/freq.htm
It shows slightly fewer than 100 channels spaced at 15KHz or 20KHz (non-uniformly).
So.... one of the really big factors is how that chip sets the frequency. Is it set arbitrarily by and external frequency command or are those frequencies built into the chip? If they are built in, you are pretty much SOL as there is no way to get 7 channels to practically access around 100.
On the other hand, if it is an external command to set specific frequencies, then you are probably OK.
A close look at the spec sheet shows that you send it a channel number in 25KHz steps. And, it accepts only a small range of frequency channel numbers. So, for this application, this chip is not much help.
You would have MUCH better luck with something that works in the maritime band.
As an alternative, consider a complete receiver, such as a scanner. Bet you can find them used. I also seem to recall RadioShack having a VHF scanner in the form of a handy-talky. You might be able to find one on eBay.
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My thought / question was this:
If the chip uses the external clock and a PLL to tune the WB channels, then mis-tune the clock by 0-2 % to scan the RR channels. Off-set the external clock to shift the PLL'd RF receive frequency.
Clearly the analog front end won't know the difference, sensitivity wise.
The Data Sheet says the AFC locks on to the WB channel. Hence one probably wants to disable the AFC, if possible.
That would require shifting the crystal many times to get the nearly 100 RR channels vs the 7 WB channels. Add to this the fact that the channel spacings don't match.
Substitute a PLL for the crystal, use just one WB channel, and use the crystal/PLL to do the tuning. I think that is the only way it could work practically.
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