DISCLAIMER

DISCLAIMER: I have no association with UVB-76 station, neither do I have any clue what is the content I am relaying. I can only assure, that the signal is received on 4.625MHz AM-modulated 900km NW from supposed origin and retransmitted unaltered. In no way can I guarantee this service, nor be considered responsible of any content re-transmitted. The only purpose for this relay to exist is because lot of people who do not have equipment or are located too far from station seem to be interested about listening to it. Should the UVB-76 station- or transmission content owners feel violated in any way, please contact me at uvb76.repeater@gmail.com and we will work it out.

Note, that because of shortwave radio signal propagation specifics the station can be more or less reliably received from around 4pm to 6am GMT on summertime. It is almost 24h audible during the winter, with short "skip-zone" blank-out around 6pm GMT.

The USB feed is considered as main source of audio today, as the voice messages are much better audible there than on the AM stream. However, the buzzer sound from the AM stream is somewhat more pleasant to listen at, so both feeds are kept simultaneously.

Thursday, March 31, 2011

SDR MK1 Shortwave Radio Receiver Alive and Kicking!

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)
  • Compatible with most free SDR software, such as SDR-Radio, HDSDR, PowerSDR, Winrad etc.
  • 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.
Internals:
  • Two channel digital downconverter (DDC) with integrated 12-bit
    analog-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.

3 comments:

  1. Very cool.

    So when will we see pre-assembled kits for sale? (:

    ReplyDelete
  2. Well .. :) The first 10 I will try to distribute around as pre-assembled, to rule out assembly-related glitches. After that, the kits will be. I'd assume in a month or so.

    ReplyDelete
  3. Hi,

    Any plans on how to get on the pre assembled list I use a softrock ensemble and a pm-sdr all the time would love to try your radio out.

    Kelvin
    kelvinm at wowway.com

    ReplyDelete