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AM/FM/SW receiver integrated on a single CMOS chip — Parallax Forums

AM/FM/SW receiver integrated on a single CMOS chip

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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2011-09-09 08:24
    This is kind of humbling to a HAM radio enthusiast. We used to spend many hours over many weeks or months trying to decide how to build the right reciever and now it is all on one tiny chip.
  • LeonLeon Posts: 7,620
    edited 2011-09-09 09:10
    It doesn't support CW, narrow-band FM or SSB, though.
  • RDL2004RDL2004 Posts: 2,554
    edited 2011-09-09 09:19
    The important thing is that it is tuned by turning an analog knob. This is the way radios are meant to work, none of this button pushing nonsense.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-09-09 10:00
    Leon wrote:
    It doesn't support CW, narrow-band FM or SSB, though.
    Yup, too bad. And since it's direct-conversion, there's no easy way to induce a BFO frequency externally, as you could with a superhet. The tragedy is that the chip includes the I/Q demod necessary for these other modes:

    Si484x_BD.png

    But the downstream DSP can only do AM and FM (mono and stereo). 'Too bad it's not reprogrammable.

    Other than that, it's a very intriguing chip.

    -Phil
  • ercoerco Posts: 20,261
    edited 2011-09-09 12:04
    Leon wrote: »
    It doesn't support CW, narrow-band FM or SSB, though.

    Nice to hear, otherwise I wasted my money on that HW-9 QRP CW rig!
  • LeonLeon Posts: 7,620
    edited 2011-09-09 12:16
    It doesn't transmit, either. :)
  • ercoerco Posts: 20,261
    edited 2011-09-09 12:38
    Leon wrote: »
    It doesn't transmit, either. :)

    Come on, Leon. ANY chip can send smoke signals.

    Once. :)
  • Martin_HMartin_H Posts: 4,051
    edited 2011-09-09 13:41
    I'm not a ham, but I used to listen to shortwave radio. My radio didn't have a BFO, but did support SSB. I found it pretty easy to identify Morse code because it would sound sort of like someone keying a mike on a regular radio, but not saying anything.

    I stopped listening to SW because the internet made it to easy to listen to radio/media from anywhere on the planet at much higher fidelity.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-09-09 13:45
    Martin_H wrote:
    My radio didn't have a BFO, but did support SSB.
    Go on... (i.e. how?)

    -Phil
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-09-09 14:07
    You can "do" SSB w/o BFO with synchronous detection.

    I don't do podcasts for the same reason that I wouldn't have listened to Radio Moscow if it had been on the telephone as an 800-number. It's no fun that way.

    These ICs might be nice for re-vamping old radios for which parts are no longer available.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-09-09 14:39
    PJ,

    I thought synchronous detection required a carrier that you could phase-lock to. How does that work for SSB?

    -Phil
  • LeonLeon Posts: 7,620
    edited 2011-09-09 15:27
    That's what I thought. I have an old ICF-2010 that uses synchronous detection for AM
  • UnknownUnknown
    edited 2011-09-09 15:38
    Bob,

    Thank you for telling us about this chip. I actually want one. It would be fun to build a radio with this chip. What kind of antenna part do I need for short wave and for the radio in general?

    What kind of features should I include? This sounds like a seperate post...

    Chuck
  • localrogerlocalroger Posts: 3,452
    edited 2011-09-09 15:45
    You can receive both CW and SSB with a direct conversion receiver. For CW you detune the local oscillator so that it beats against the received signal, essentially making IT the BFO. For SSB, you tune the local oscillator to where the carrier should be and, again, it becomes the BFO. The problem is that you can't narrow the selectivity the way you can with a superhet, so there's more interference. But I have a 70's era TEN-TEC QRP transceiver whose receiver is direct conversion, sharing a local oscillator with the transmitter, and I can verify that it receives both CW (as per its intended use) and SSB if tuned properly. Whether the chip can be used this way really depends on the functions available in the mysterious "DSP" block.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-09-09 15:55
    Well, okay, LO: a BFO by another name. :)

    Actually you can adjust the selectivity of a DC receiver -- and even limit reception to one sideband or another -- by using a DSP downstream from the I and Q mixers. With separate I and Q outputs, just about any signal can be demodulated, using the right algorithm. That's why I thought it would be nice if the DSP in the Si484x were reprogrammable.

    -Phil
  • rogersydrogersyd Posts: 223
    edited 2011-09-09 17:23
    Mouser has a neat looking demo board for 50 smackers. part number 634-SI4844-DEMO
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-09-09 17:37
    Phil et Leon,

    It's on my Drake R8B which I got just in time for the bottom to fall out of international broadcasting. Good fortune never comes with both hands full.

    "With the addition of audio phase shift networks, it is possible with synchronous detection to receive SSB, or just one sideband of a DSB signal, by the phasing method. The phasing method is more familiar as a SSB generation method, but the inverse process works equally well for SSB reception.
    "To obtain SSB reception, the I and Q audio signals are applied to active audio phase shift networks. The networks have a flat frequency response characteristic but exhibit a phase shift which is frequency dependent. This kind of network is known as an
    allpass filter (an I-channel allpass and a Q-channel allpass). These two networks have a nearly constant 90 degree audio phase difference (+/- 3 degrees) over the range 50 Hz - 12kHz, which provides a minimum of 31 dB unwanted sideband suppression over that range."
    -- W9GR

    I too have a "2010" I have a ICF-SW7600GR. I thought it would be a step up from my ICF-2002 (which had been a solid performer except for its known tone setting anomaly), but not so much as I found the selectable sideband responses horribly unacceptibly asymetrical (misaligned, endemic, this was noted by WRTH, PWBR, and others), unworthy of Sony to say nothing of my own discerning ears.
    The Drake R8B left the Sony in the dust - and cost a lot more. I remember having been able to pull out All India Radio on 5980 (5970?) with BBCWS booming beside it on 5975 like it wasn't even there.
  • Martin_HMartin_H Posts: 4,051
    edited 2011-09-09 17:39
    Phil, my radio is a Sangean 909 which they call a dual conversion receiver. In the SW bands it can be set to AM, USB, or LSB. It is pretty automatic but limited in its tuning and conversion modes.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-09-09 18:53
    Martin,

    According to the info I've been able to glean from the web, the '909 has a BFO that's active during SSB reception, so you should be able to receive CW in SSB mode without a problem.

    -Phil
  • Martin_HMartin_H Posts: 4,051
    edited 2011-09-09 19:09
    Phil, thanks I will have to try that next time listen to ham bands.
  • Bob Lawrence (VE1RLL)Bob Lawrence (VE1RLL) Posts: 1,720
    edited 2011-09-10 11:55
    Is it affordable?

    Pricing and Availability
    The Si484x multi-band receivers are available in a compact 24-pin SSOP package, enabling cost-efficient, single-sided PCB designs and easy handling in manufacturing lines. Samples and production quantities of the Si484x radio ICs are available now. The Si4840 AM/FM radio IC is priced at $1.81 (USD), and the Si4844 AM/FM/SW radio IC is priced at $1.96 (USD), both in 10,000-unit quantities. To ease radio system design, Silicon Labs offers the Si4840-DEMO and Si4844-DEMO evaluation kits, each priced at $50.00 (USD MSRP). For more information about Silicon Labs’ Si484x wheel-tuned, digital-display radio ICs and to purchase samples and development tools, please visit www.silabs.com/pr/radio-receiver.







    @ Chuckz


    re: $1.96 (USD), both in 10,000-unit quantities.

    One for you and one for me , we only need 9998 more people interested and we can get a great price. :)
  • TorTor Posts: 2,010
    edited 2011-09-10 12:35
    Well, for that price I guess I could go for two.. so, 9996 to go?

    -Tor
  • UnknownUnknown
    edited 2011-09-11 05:35
    Bob Lawrence (VE1RLL) wrote: »
    The Si4840 AM/FM radio IC is priced at $1.81 (USD), and the Si4844 AM/FM/SW radio IC is priced at $1.96 (USD), both in 10,000-unit quantities. To ease radio system design, Silicon Labs offers the Si4840-DEMO and Si4844-DEMO evaluation kits, each priced at $50.00 (USD MSRP).

    How much could someone build a simple radio for? I priced the parts on one of these Hack A Day Alarm Clocks and the price was around $100 due to the cost of the parts people wanted to use.
  • LeonLeon Posts: 7,620
    edited 2011-09-11 05:42
    A simple AM receiver could be built for $5 or so.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2011-09-11 07:19
    How much could someone build a simple radio for?
    How "simple" a radio do you want?

    Even in the jaded Internet Age, a crystal set will still demod AM radio.

    Anyone for a ZN414?
  • wasswass Posts: 151
    edited 2011-09-12 20:29
    I saw the announcement of this chip on a few sites and ordered the evaluation board from Digikey, they have it in stock for less than the suggested price. This is an amazing little chip!

    The evaluation board is very simple: just the SI4844 chip, some unidentified potted micro driving a small LCD, small amplifier chip for headphones, antenna options and various switches to let you test all the functionality. The included documentation is pretty detailed in how to program it and there is a lot of testing information touting its sensitivity and low noise characteristics. Unfortunately the micro and firmware is totally closed off so you can't hack it, but then again the idea is to get you to buy the chips and make whatever from scratch. The firmware that they wrote to control this is pretty quirky, but good enough to give you the basics of what can be done. The board itself is single sided with a bunch of jumpers, pretty cheap but to the point.

    Anyway, the touted sensitivity and low nose is all true! This is an incredible receiver on AM broadcast, FM and SW broadcast. I compared it side by side with my DE1103 and it's definitely nicer to listen to on all bands But don't even think about using the horrible earbuds they provide plug in something high-quality. Because this is AM only, I can't speak to the selectivity well, but the sensitivity seems better than speced almost to the level of the DE1103.

    I don't know if I like the whole concept of and pot feeding an 8-bit ADC whch then digitally selects a limited range of frequencies, it's not all that user friendly if you ask me. The BAND selection input is also an ADC with 12 possible values (voltages). This is "analog" interface. But you can ignore all that and feed it whatever frequency you'd like via the 2-wire communication line with you favorite controller chip, uses a rotary encoder and make a "real" (and tiny) radio out of this chip.

    The documentation on this is not on the SI site yet, there's just a two page data sheet that doesn't tell you much. I'm still working my way through it, but let me know if I can answer any questions about it.

    73,
    -w2lp
  • RDL2004RDL2004 Posts: 2,554
    edited 2011-09-12 22:40
    I was placing a Mouser order today and I was going to buy a couple of the chips, but I couldn't find any info at Silicon Labs on how to actually use them. All I could find was that 2 page data sheet, which wasn't very helpful. I looked at one of their other (similar) chips and it looks like it will only take a small number of other parts to turn these into an actual radio. Now if somebody would only make a breakout board for that little 24 pin ssop chip.
  • TonyWaiteTonyWaite Posts: 219
    edited 2011-09-13 06:50
    Hi,

    Digikey have a 24-pin SSOP to DIP adaptor:

    24-351000-10-ND

    T o n y
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