[aprssig] APRS SDR

[Jeremy McDermond]

On Dec 15, 2010, at 1:40 AM, Matti Aarnio wrote:

> On Mon, Dec 13, 2010 at 01:53:42PM -0800, Jeremy McDermond wrote:
>> On Dec 12, 2010, at 8:05 AM, Matti Aarnio wrote:
>> 
>>> Having a special SDR hardware that takes application bits in on one end,
>>> and puts IF/RF waveforms out on other is usually seriously more expensive
>>> approach.  A mid-scale Xilinx Virtex-IV, and 100 Msps ADCs/DACs does cost
>>> several kilo-dollars, or more commonly tens of kilo-dollars.
>> 
>> It's not that bad.  The OpenHPSDR project is using the following parts:
>> 
>> LTC2208 (130 Msps 16-bit A/D converter): $130
>> AD9744 (210 Msps 14-bit D/A converter): $12.68
>> Altera EP3C40 (39600 gate Altera FPGA.
>> Largest leaded array available from Altera):  $78.50
>> 
>> Those are prices from DigiKey today.  The current OpenHPSDR system in
>> totality is in the low kilo-dollars range.  One of the new designs should
>> hopefully bring a price in the less than kilo-dollar range.
> 
> While I might consider blowing my yearly hobby electronics project budget
> on OpenHPSDR or SDR-IQ, commercially viable "APRS SDR" is still a _cheap_
> microprocessor that has ability to AD/DA of baseband waveforms, and do DSP
> processing on them.  Total system price assembled, tested and delivered to
> my mailbox under USD 100.

No real disagreement here.  The point was that "kilo-dollars" and "tens of kilo-dollars" were probably a factor of ten off.  The ADC/DAC/FPGA is well below one kilo-dollar ($1 x 1000 = $1000).

> A system where one ADC alone costs more than that.  Very few will buy it.
> Not to mention its power requirements.

Agreed.  What would be cool is a VHF Softrock.  That would allow folks to use their existing soundcard to digitize the baseband, and just use it as a QSD/QSE transceiver.  My understanding is that the quadrature mixers at that frequency start to get a bit more expensive, and might drive the costs above your theoretical $100 price point.

> See OpenTracker and TinyTracker.  They are commercially viable.
> They even do modem bits partly in software.
> 
> There are so many ways that one can understand what "SDR" means...
> Some apparently understand it to include applications like UI-View.

Well, soundmodem could be interpreted to be SDR at some point, but as someone else pointed out, that's more software defined modems.  SDR, at the current price range, doesn't bring much to the table for APRS.  Using fast ADC/DACs really allows you to see more bandwidth. The application might be to decode/transmit on more than one channel at once.  The cool app might be for a $500 transceiver that can run 1200bps on 144.390, and 9600 VHF on an alternate channel of some sort.

>> Jeremy McDermond (NH6Z)
> 
> 73 de Matti, OH2MQK

--
Jeremy McDermond (NH6Z)
Xenotropic Systems
mcdermj at xenotropic.com