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Tom Clark NASA Goddard/NVI k3io@verizon Socorro NM Nov 1,2011

Tom Clark NASA Goddard/NVI k3io@verizon.net Socorro NM Nov 1,2011. A Low-Cost Phase Cal Monitor and RFI Spectrum Analyzer for VLBI2010 Mark-5 / Mark-6 using Cheap, COTS Software Defined Radio (SDR) Hardware & Software Gleaned from the World of Amateur Radio.

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Tom Clark NASA Goddard/NVI k3io@verizon Socorro NM Nov 1,2011

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  1. Tom Clark NASA Goddard/NVI k3io@verizon.net Socorro NM Nov 1,2011 A Low-Cost Phase Cal Monitor and RFI Spectrum Analyzer for VLBI2010 Mark-5 / Mark-6 using Cheap, COTS Software Defined Radio (SDR) Hardware & Software Gleaned from the World of Amateur Radio

  2. In the Mark-3 world we monitor Phase Cal Signals in the final baseband (“video”) IF 10 kHz USB Only THE “OLD” WAY f=325.99 10 kHz BPF & Scope LNA IF Amp HP 3528 FFT Anal PCAL LO=8080 THE “NEW” WAY with $600 SDR and a small Netbook PC 10, 1010,2010…. kHz USB or 990,1990, 2990….kHz LSB with 50+ dB Dynamic Range

  3. In this case, we look at the Phase Cal signal at 8080 + 325.99 – 5.990(LSB) = 8400.000 In this case, we see a span of ±600 Hz around the Phase Cal “rail”. The Resolution Bandwidth (RBW) is 0.85 Hz and the screen is showing a 40 dB amplitude range.

  4. In the new Mark-5 Digital Backend, all the analog Video Converter functions become Digital. And the equivalent of the Mark 3/4 VC’s USB/LSB BNC jacks exists only inside a Xilinx FPGA. RDBE = Digita l Backend = 2nd LO & Digital Baseband Filters & Formatter UDC = UpDown Converter = First LO Mark-5 Disc Recorder LNA Microwave Fiber PCAL

  5. In the VLBI2010 configuration, the RDBE (a.k.a. ROACH Board) performs all the (formerly analog) IF Back-end functions: 2-Bit Samples for each 32 MHz PFB channel 32 Channel PolyPhase Filter Bank “”Formatter”” Sampler & A/D Conv 0.5-2.5 GHz IF IN Disk Array

  6. Russ McWhirter has recently provided me with an RDBE with evaluation v1.4 firmware 2-Bit Samples for each 32 MHz PFB channel “”Formatter”” 32 Channel PolyPhase Filter Bank Sampler & A/D Conv 0.5-2.5 GHz IF IN Disk Array Baseband One-Bit Monitor Port Isolation & Multiplexer Added Firmware Sign-bit Monitoring Port

  7. Using One-bit (sign) Samples

  8. The Attributes desired for the Monitor SDR (in order of desirability) • Oscillators (RF Conversion and sampling) in the SDR should be “clean” to verify coherence. • Oscillators should be derived from Maser master clock. • If you switch between 2 frequencies A>B does it return to >A at the same phase? • Can the timing be synchronized with the house 1PPS reference?

  9. Some Commercial SDRs RF Space (http://www.rfspace.com) in Atlanta GA makes several SDR’s, in particular: • The $500 SDR-IQ (used in the previous example) covers the DC-30 MHz range with up to 192 kHz bandwidth. Interface is USB. This is competent small, cheap SDR that is a very useful piece of test equipment that fails in all 4 criteria • The new $3700 SDR-IP looks like a perfect VLBI Phase Cal monitor. It’s internal clocks can be locked to the Maser for fully coherent system monitoring. It interfaces via Ethernet and UDP packet covering up to 2 MHz bandwidth in the 0-34 MHz frequency range. I hope to be able to try one soon. The SDR-IP appears to meet all 4 criteria.

  10. Some Commercial SDRs The $800 “Quicksilver” QS1R (http://qs1r.wikispaces.com or http://www.srl-llc.com/ or http://groups.yahoo.com/group/qs1r/) by Software Radio Laboratory in Columbus OH shows much promise. It covers DC-62 MHz (or up to ~500 MHz when oversampled) with up to 2 MHz bandwidth. The QS1R interfaces to its PC by USB. The entire design and all its support software is “open” licensed. This unit meets Criteria 1, 2, & 3 and possibly can be modified to also meet 4.

  11. Some Commercial SDRs The Italian Pegasus SDR is available for $1000 in the US (http://www.universal-radio.com/catalog/commrxvr/0122.html) is quite similar to the QS1R but only covers 40 MHz. It is essentially a clone of the QS1R

  12. Commercial SDR that may be relevant GNU Radio (http://gnuradio.org/redmine/wiki/gnuradio) represents a major collaborative effort from a number of sources. All the GNU software is supported on the USRP hardware available from Matt Ettus (http://www.ettus.com/). FYI – Ettus was recently acquired by National Instruments and I anticipate NI will be making a splash in the SDR world soon. See the gnuradio & ettus web sites for more details.

  13. The Final Bottom Line • 2 weeks ago I did a crude, partial test of Russ’s v1.4 firmware on a QS-1R and an SDRIQ. • Given the known limitations on the test setup, everything worked precisely as planned. • Not tested were end-to-end coherence and the 32-was multiplexer switch. • Not implemented yet is a simple thru-path to operate the multiplexer switch.

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