5
$\begingroup$

Is there an IC out there that implements all, or most all, of a simple FM receiver in the VHF range? I'm interested in doing some experiments with using DTMF over the air for tele-commands and the like, and I'd like to keep the receiver electronics as simple as possible. The idea is to have a very simple receiver from which I can pipe the audio output to a DTMF decoder IC and then send signals to an Arduino or Raspberry Pi or something of that nature.

I think I may be looking for something like the TDA7000 chip but I'm not clear on what frequency range it can support. It also appears that it may be obsolete / hard to source? I seem to mostly only see ebay vendors selling these. Is there perhaps a more modern successor this this chip that I should be looking at?

This Silicon Labs chip also looks promising and the frequency range is clearly spec'd, and should work for what I want to do, but the problem is that it's only available in a surface mount QFN package, and I'm really not familiar with soldering SMT devices. Something in a good old fashioned DIP package would be great if something like that exists.

Edit: the more I look at this stuff, the more confused I get. It looks like a lot of the IC's that are out there that are billed as "RF receivers" assume you're encoding data in FSK or something, and they want to give you decoded data. Sadly, that's not what I want. I just want the audio demodulated from FM. On that front, it appears that there are "receiver" IC's that will demodulate FM and give you audio, but from what I can tell, they all expect to receive as input, an "IF" (Intermediate Frequency) of 10.7mhz or 45mhz or something... which if I'm reading this right, implies you need another circuit - a mixer - in front of the receiver to downconvert the RF.

This is starting to seem overly complicated, so I may just drop the idea of looking for an IC to do this stuff and just roll it the old fashioned way. That said, if somebody reading this can point to a nice, simple IC based way (using no more than 2 or 3 IC's preferably, 1 would be better) to go from RF -> demodulated audio, it would be appreciated.

$\endgroup$
  • $\begingroup$ Literally on the second page of the TDA7000 datasheet, you have the input frequency range which is from 1.5 MHz to 110 MHz. Also MHz and mhz are not the same. $\endgroup$ – AndrejaKo Sep 3 '16 at 14:17
  • 1
    $\begingroup$ If you want to be pedantic, there is no such thing as "mhz". There are only mHz and MHz. But the reality is, nobody here really had any problem understanding what I meant. Context matters. :-) $\endgroup$ – mindcrime Sep 3 '16 at 22:17
1
$\begingroup$

I don't know much about receiver-on-a-chip devices, although both of the chips you mention look promising. I'd be very surprised if the TDA7000 couldn't handle VHF frequencies.

The TDA7000 is almost certainly not being manufactured, but I wouldn't let that bother you. octopart.com shows two resellers that have the parts in stock, which means that they will be available for a few more years yet in small quantities. I wouldn't design a product to be manufactured around the chip, but if you're just experimenting then you can expect eBay sellers to have them for a few years longer.

The Si4362 is carried by the usual distributors, so it's likely still being manufactured.

You could attach the Si4362 to a DIP adapter, which would allow you to plug the chip into a 20-pin DIP socket, but you'd still need to solder the chip to the adapter. Soldering SMT parts by hand is easier than it looks; Adafruit has some great advice.

Good luck, and let us know how you do with a comment.

$\endgroup$
  • 1
    $\begingroup$ Sounds good. I need to learn to do SMT soldering anyway, so maybe I'll bite the bullet and give it a try with this. Thanks for the info! $\endgroup$ – mindcrime Sep 1 '16 at 17:18
2
$\begingroup$

another way to do it would be to use a cheaply available RTL-SDR device (like a 5$ DVB-T receiver), and then go software-defined from there.

rtl_fm can do FM demodulation in the needed frequency bands and multimon-ng can demodulate DTMF tones and signaling and give you the data.

A simple Raspberry Pi has enough processing power to do something like this.

$\endgroup$
1
$\begingroup$

I think I might have found something. The Motorola MC3362 is described in the datasheet as:

The MC3362 is a complete FM narrowband receiver from antenna input to audio preamp output. The low voltage dual conversion design yields low power drain, excellent sensitivity and good image rejection in narrowband voice and data link applications. In the typical application (Figure 1), the first mixer amplifies the signal and converts the RF input to 10.7 MHz. This IF signal is filtered externally and fed into the second mixer, which further amplifies the signal and converts it to a 455 kHz IF signal. After external bandpass filtering, the low IF is fed into the limiting amplifier and detection circuitry. The audio is recovered using a conventional quadrature detector. Twice–IF filtering is provided internally.

http://www.futurlec.com/Motorola/MC3362Ppr.shtml

It also covers up to 200mhz. Sadly these also appear to be somewhat obsolete but Futurlec seems to have a supply of them, and they're in a nice old fashioned DIP package which I like. (Hey, I'm old-school, so sue me!)

Think I'll order a couple of these and see if I can do something with them.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.