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[Discuss-gnuradio] "Open-Hardware"

From: Patrick Strasser
Subject: [Discuss-gnuradio] "Open-Hardware"
Date: Wed, 12 Jan 2011 00:13:15 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.6) Gecko/20050602 Thunderbird/1.0.2 Mnenhy/

First, let's change the topic. This is overdue.

schrieb Moeller on 2011-01-11 07:21:
> On 10.01.2011 02:22, Marcus D. Leech wrote:
>> The SSRP, as far as I can tell, is dead. Last status update was nearly 4 
>> years ago.
> The development stopped apparently. But at least he has a working design for 
> the RX part.
>> o The ADC board (single-channel, thus cannot handle direct-conversion with I 
>> and Q sampling) $120.00
>> o Uses an Off-The-Shelf ElraSoft FX2 board, which in 2007, sold for $89.00
> Oh, forgot about the USB interface, so it's about $200. That would be my 
> limit for a home-product.

As I said before, I think the Elrasoft board is more than completely
overpriced. There must be something cheaper out there. Or it has to be
created. I could imagine that an Open Source EZ-FX2 with voltage
regulator and a set of sensible connectors would be a great tool for a
lot of people.

For comparison:
The Arduino costs like 25€ nowadays. Recently they changed their USB
interface from a limited dumb FTDI to a Atmel USB microcontroller
Atmega8U2. The Arduino can now act not only as a serial divice, you can
make it look like lot of things: HID (mouse, keyboard, joystick), mass
storage, audio device, MIDI interface, most of them host and device.

>> Ok, so maybe we can run the ADCs and DACs at a lower rate, so that we can do 
>> the DDC and decimation in the FX2? I'd be
>> *astonished* if it could keep up with input rates beyond roughly about 
>> 200Ksps complex, which is cheap sound-card territory. Oh dear.
> Not if a modern PC with appropriate programming (SSE extensions) would do the 
> decimation.

You need the decimation on the device side of the USB connection to
reduce the amount of data sent over it. The absolute limit isbetween 32
an about 40MiByte/sec. Divided by 16bit=2byte per sample is 16-20MSPS
real-valued or 8-10MSPS complex-valued. Either you reduce the sampling
rate or you decimate. That rate should be more than sufficient for all
but the most demanding experiments. The only common interesting signals
that need more bandwidth are TV (6-8MHz), GPS (2-20MHz?), WLAN (20MHz),
All of them in higher bands, where mixing the signal down into the ADC
frequency range would be needed.

An other way would be to change the interface, which would very likely
be Gigabit-Ethernet.


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