After almost memorizing the National Semiconductol LM97593 chip datasheet and getting intimate with the DSP registers setup inside, the SDR MK1 is now working!
NB! There are some minor changes to the schematic and layout on the SDR project page, I will post errata and new files in next few days together with software developed so far.
This is what it looks like when assembled :)
It has two channels, both equipped with 32MHz lowpass filter, so two different antennas can be connected to the reciver. Replacing the filter with the bandpass, any 30MHz frequency region between 5kHz and up to 300MHz can be acessed, as the rest of the chip is capable of handling this range. The power connector is only needed if your USB connector is not able to supply 500mA of power, what most of the USB ports will, but some dont. In that case you will need external 6V adapter.
Normally, the board is connected only through the USB what is supplying power to the SDR and is used to transmit audio feeds and control information.
Technical specs so far:
- 5kHz to 30MHz frequency range
- 0.02Hz tuning resolution
- 123dB total dynamic range
- 64MHz internal sampling rate
- User Programmable AGC (automatic gain control) with enhanced Power Detector
- 48kHz/16-bit output sample rate (upgradable to at least 96kHz/16bit in near future)
- Possibility for tuning and setup using serial port console screen
- Powered from USB port or external adapter
- 2x BNC Antenna connectors (Mfg: Rosenberger)
- Max current consumption 470mA
- Open software and hardware design for DIY development, filter upgrades etc.
- Two channel digital downconverter (DDC) with integrated 12-bitanalog-to-digital converters (ADCs) and automatic gain control
- Double DVGA (digitally controlled variable gain) front end amplifiers with +36dB maximum gain and 600MHz bandwidth
- RF filters: 7-pole Chebyshev lowpass filters
- Channel Filters (DSP): Fourth Order CIC followed by 21-tap and 63-tap Symmetric FIRs
How well does it deliver? Well, the two receivers I am intending to compete with are Perseus from Microtelecom and SDR-IQ from RFSPACE.
Both are top of the class and share the same arhitecture as SDR MK1. I havent been able to play around with neither of them myself, but looking at the screenshots in the web, the MK1 measures up quite well, especially considering that the screenshot below is made with the very first set of DSP chain parameters what are not totally off, but are still far from optimal values.
This is what the UVB-76 looks on screen when received with SDR MK1
The screenshot taken last night is somewhat special, as it shows two signals visible next to buzzer. The top one is an encrypted voice traffic, referred as "Sailors Cry". The bottom signal is the Russian USB (open) voice traffic on 4627kHz what was very active last night and was part of the of massive commcheck around different radio posts in the region. The two may be related or may be not, but they seem to share exactly the same frequency.
Further left is the Tallinn Volmet and some new "jet" type of transmission, what has appeared lately, harrassing it.
There is still some software work ahead on firmware to get the SDR audio output to at least 96kHz/16bit and possibly 192kHz/8bit. While I am now investigating if the 96/16 ispossible to achieve with AT90USB1287 processor with the standard Windows USB 1.0 audio drivers, both look doable with proprietary driver.