Tuesday, October 07, 2014

Status Update

QS1R Receivers are in stock ready for immediate shipment.  An update to SDRMAX V is in the works also.  We are working on some new products that will be available next year.   There is no plans to discontinue the QS1R and it will be supported far into the future.

Monday, January 28, 2013


USPS has raised its rates again on Domestic and International Priority Mail shipping.  This seems to have become a yearly thing.  The only upside is that it is still less expensive than UPS and FedEx for both domestic and international shipments.

For the 2012 Christmas Holiday Season, we saw a surge in QS1R orders.  By mid January 2013, we sold out of our current stock of QS1R receivers and have ordered another assembly quantity from our contract assembler.  Luckily, there were no delays caused by parts shortages or back orders.  We will begin shipping new QS1R RevD units from this new lot at the end of January 2013.

Wednesday, July 25, 2012

Rumors and other nonsense...


Recently I have seen this subject brought up again when it should have been put to rest a long time ago.  There was a talented volunteer software developer (Cathy Moss of the UK) who developed a GUI software application for the QS1R (called Panoptos or SDRMAX III) who eventually stopped developing the software.  There has been much speculation on why she left the project. These recent references to Cathy Moss, who volunteered to write a GUI that worked with my QS1R server, demonstrates how ridiculous fabrications, gossip, and rumors can become.  Everyone wants a dramatic soap-opera explanation, it seems.  Cathy Moss decided to stop writing code for personal reasons (which I will not discuss out of respect for her) and not because I stopped her or forced her out as some ridiculous rumors have claimed.  Cathy Moss is a very talented and prolific programmer as anyone can see, and so I offered her a paid programming position which she declined for personal reasons/obligations. Cathy Moss was also contacted by multiple SDR manufacturers and some HPSDR group members with offers asking her to support their hardware instead, all of which Cathy Moss declined.  Cathy is a still a member of the official QS1R Yahoo group and we occasionally exchange emails on the subject of SDR.  As with all volunteer software efforts, the volunteer is under no obligation to continue to write or support software.   Interests change, personal circumstances change, and developers burn out or move on. Cathy has indicated that she may do some more software development at some point in the future, but for now she is too busy with personal circumstances. She would certainly be welcomed back by me for sure.

Friday, September 02, 2011

September 2, 2011

News section has been added to the QS1R Wiki

Wednesday, August 10, 2011


For updates and latest information on the QS1R Receiver please visit the QS1R Wiki at:


Monday, July 05, 2010

QS1R Update



QS1R Receivers are now shipping immediately upon ordering. The next version of software called SDRMAXIV is under development. The QS1T and RFFE1 designs are being integrated into the SDRMAXIV software. Development has started on a transciever board which includes an integrated DSP.

Monday, December 21, 2009


WPF = a natural for Software Defined Radio GUIs

(stay tuned for further information)

Saturday, November 21, 2009

QS1R Status

QS1R Receivers are now shipping within 7-10 business days after order. The current revision of QS1R is RevD. The future QS1T Transmitter board and RFFE1 front end board are both still at the pre-production stage.

Tuesday, February 03, 2009

RFFE1 Why you may (or may not) need it

RFFE stands for "Radio Frequency Front End" and the "1" stands for the first version (0-62.5 MHz coverage).

When I was designing the QS1R board, I had to decide whether to include bandpass filtering and RF amplification on the board. In fact the initial prototypes "RevA" included RF amplification on the QS1R board. Unlike another DDC based direct sampling receiver "Perseus", QS1R was designed to be more than a SW receiver. In addition to a SW receiver, QS1R was meant to facilitate experimentation in the RF spectrum up to at least 300 MHz. I finally settled on a 55 MHz low pass filter (which can be bypassed) and no active components in front of the ADC on QS1R. Any active devices, bandpass filters, or attenuation would be added by a separate board such as the RFFE1.

The antenna that I use for my QS1R is a center fed, non-resonant dipole at 50 feet. The total wire length is about 240 feet with only about 100 feet of that running horizontally. It is fed with 450 ohm ladder line connected in the house to a 4:1 balun. The last 10 feet of feed line is coax to the QS1R from the balun. I do not use a tuner with this antenna for receiving. In my neighborhood, all of the utilities are under ground so the noise level is typical or maybe a bit less than the noise level of a suburban area. With this antenna and the QS1R, I find that band noise is always greater than the QS1R's noise floor until about 21 MHz. I arbitrarily have assumed (possibly incorrectly) that my antenna installation is average. Any amplification in front of the QS1R's ADC (below 21 MHz) is only a detriment in this case. The QS1R typically overloads at +9 to +10 dBm so amplification would degrade the strong signal handling capability of the receiver. The largest signal level that I have observed at my location has been about 0 dBm in the 0 - 62.5 MHz region. Contrary to what some may believe in the above case for the QS1R, bandpass filtering will improve nothing and, because BPFs typically have some loss, degrade the sensitivity slightly. As long as the atmospheric or band noise is greater than the noise floor and the signals levels in the 0 - 62.5 MHz region is below +9 dBm, bandpass filtering and/or amplification does not gain anything.

By providing RF front end add-on boards such as the RFFE1, a front end (if even desired) can be tailored to the specific application of QS1R and will not impose a significant cost increase to the QS1R board for those who do not need the RFFE(1) boards. The QS1R is capable of under sampling up to ~ 500 MHz, so it will be possible to design RFFE(x) boards that will allow coverage up to ~ 500 MHz. For example, RFFE2 would provide low noise amplification, bandpass filtering, and attenuation of the range of 125 to 187.5 MHz ( including 2 meter ham band coverage). There is some interest by individuals in FM band Dxing which could be provided by a RFFE(x) board.

The RFFE1 board is designed to fit within the existing QS1R Aluminum enclosure by replacing the front and rear end plates with new end plates (supplied with RFFE1). RFFE1 has switchable attenuation, two stages of switchable low noise amplification, and switchable filtering. It is controlled via the QS1R's I2C bus and derives its DC power from QS1R. The RF amplifiers provide up to 26 dB of gain (noise figure ~ 2 dB). With the attenuation switched in, the QS1R can handle signal levels up to +29 to +30 dBm without overload of the ADC. Each RF amplifier provides ~ 13 dB gain. With both amplifiers switched in and attenuation switched off, the QS1R can handle signal levels up to -17 dBm (or -4 dBm with one RF amp switched in) without overloading the ADC. The QS1R's IP3 is > +50 dBm so the RF amplification was designed to not degrade the IP3 excessively. With the amplifiers switched in, the IP3 is ~ +32 to + 33 dBm. Contrary to what some have speculated elsewhere, the RFFE1 does not use the LTC6400-20 ADC driver that HPSDR Mercury uses for a preamp. In HPSDR Mercury, the 20 dB amplification provided by the LTC6400-20 is always present - the preamp is bypassed by switching 20 dB of attenuation in front of the LTC6400 ADC driver providing a net gain of 0 dB. In the RFFE1, the two RF amplifiers are individually switchable in and out of line and have their own impedance matching and filtering networks for enhanced performance.

With any amplification in front of the QS1R's ADC and without filtering, the whole 0 - 62.5 MHz region is amplified equally - so any signal within this range could possibly overload the ADC if its signal strength amplified by the gain of the RF amp exceeds +9 to +10 dBm. This is where band pass filtering is an advantage. It is not easy to design the filtering so that adequate attenuation is provided out of band as well as not degrading the IP3 performance of the receiver. Luckily we are not dealing with an analog radio, so the assumptions about exactly what is needed in a conventional receiver does not necessarily apply to direct sampling receivers such as the QS1R. I spent a very large amount of time in experimentation and testing to come up with a filtering system for RFFE1 that does not degrade IP3 performance. I was surprised in what I found and eventually decided on, but that is a subject for a future blog entry ;-). I did a lot of modeling of various filter networks to determine the RF current in each inductor given the physical and electrical characteristics of each type of inductor. This helped me chose the best filter arrangement and inductor type for the RFFE1 without degrading IP3 as much as other competing receiver's bandpass filters degrade IP3.

So who needs a RFFE1? Here are my guesses:

1. Anyone who wants to use QS1R above ~ 18 MHz with an average antenna system. This includes 10 and 6 meters.

2. If your antenna is less efficient and you have determined that the noise floor of QS1R is above the band noise at some point below 18 MHz. An easy way to determine this is by disconnecting your antenna while watching the noise floor or s-meter in SDRMAX(II/III). If the noise floor increases by at least 6 dB when you reconnect your antenna then you have adequate sensitivity at that frequency.

3. If your antenna does not provide a 25 - 75 ohm impedance to QS1R. Antennas that deviate far from 50 ohms will manifest as severely reduced sensitivity with QS1R. In my case with my non-resonant 450 ohm ladder line fed dipole, a 4:1 balun is all that is required for me to have adequate sensitivity up to about 21 MHz.

4. Signal strengths in your location in the 0 - 62.5 MHz range exceeds +9 dBm at the antenna input to the QS1R receiver. In this case the switchable filtering and/or attenuation provided by RFFE1 will eliminate the overload. QS1R and SDRMAXII provides the nice capability of viewing 50 MHz of spectrum at once - it is easy to see the maximum signal levels your are receiving in that range.

5. RFFE1 has two switchable antenna inputs as well as additional static/surge protection. RFFE1 also provides a connector for external receiver mute input, two protected general purpose IO lines, as well as an external connection to the QS1R I2C bus for external relay control and/or switching. While these options are not necessary for the functioning of QS1R, they are nice to have in some cases.

Who does not need a RFFE1?

1. If your operation is below ~18 MHz and your antenna system is adequate (see 2 and 3 above) and you have no overload problems (you don't see your "clip" LED on the front of QS1R illuminating) then you won't gain much with RFFE1. This generally includes using QS1R with transverters and for an IF receiver with other receivers/transceivers.

Exact performance numbers for RFFE1 will be posted in the near future as well as pricing. Hint: The price of QS1R and RFFE1 together will not exceed the price of competing direct sampling receivers!

Wednesday, July 16, 2008

SDR Discussion

Please subscribe to the QS1R yahoo group at:


for the latest news and discussion on SDR topics and the QS1R.


Phil N8VB

Wednesday, January 30, 2008

Production QS1R RevC Pictures

QS1R Webpage is up:


Orders for the first group of QS1Rs from assembly will be taken very soon. Please keep checking the website.

See the latest news at:


Here is a picture of a production QS1R RevC board:

Tuesday, October 30, 2007

QS1R REVB Picture


History of HPSDR Mercury and Quick Silver

History of HPSDR Mercury and Quick Silver

Philip Covington, N8VB

Early HPSDR and XYLO

In 2005 I started a High Performance SDR (HPSDR) project which was to consist of a motherboard carrying a FPGA/USB 2.0 interface and power supply with the provision for plug in modules through 40 pin headers. I had planned a narrow band high dynamic range module based on a QSD/DDS/PCM4202 audio ADC and a wide bandwidth module based on a high speed 16 bit ADC:



I soon selected the LTC2208 ADC from Linear Technology. A representative from Linear Technology came across my blog (http://pcovington.blogspot.com/ ) and offered evaluation boards and samples to support the project.

At about the same time my HPSDR project came about, Phil Harman, VK6APH and Bill Tracey, KD5TFD were interested developing a sound card replacement to be used with the SDR-1000 and had started developing with a FPGA development board (XYLO) that had a high speed USB 2.0 interface. They formed the XYLO SDR group to support this. In March 2006, Phil Harman proposed that we merge my HPSDR project and XYLO SDR group into a common project since our goals were similar. By the middle of March 2006 an announcement was made that the groups would merge and the HPSDR.org website was set up.


One of the first tasks was to define a backplane since various backplanes, such as passive PCI, were being proposed. I volunteered for the task which became the ATLAS backplane:



We had an early volunteer to design an ATLAS plug-in FPGA/USB board to replace the XYLO board, but unfortunately the volunteer was not able to follow through with the task. I agreed to do the design for this board which became the HPSDR OZY board and to provide for the possibility of controlling a SDR-1000 through the OZY’s IO ports that simulate a PC parallel port:


Early HPSDR Mercury

Soon after the OZY design was done I began to pursue Mercury. I initially used the Linear Technology supplied evaluation board for the LTC2208. In May of 2006 I became very busy with a work project so I asked Phil Harman if he would like me to send him one of my LTC2208 evaluation boards to play with. I also sent Phil a Crystek low phase noise crystal oscillator that I had chosen as a candidate for driving the encode clock of the LTC2208 ADC. In the link below you can see the Mercury breadboard connected to the OZY. The LTC2208 evaluation board can be seen plugged in vertically to the breadboard with the RG 174/U cable running to the top of it:


Quick Silver Version 1

In late 2006 I decided to design a board that I called Quick Silver (related to Mercury) which would become the initial prototype for HPSDR Mercury:



The initial thought about the design of HPSDR Mercury was that it would use either an Analog Devices AD6636 or AD6620 Digital Receive Signal Processor chip. The ADC6636 was only available in BGA packaging so I chose to use two AD6620 DDCs on the Quick Silver (also called QS1R REV AB). I wanted to investigate whether the AD6620/6636 was suitable for use with the LTC2208 in a HF receiver and also to test the choice of low noise Crystek oscillator encode circuitry which would be critical in determining the LTC2208 ADC’s performance.

It quickly became clear that the AD6620/6636 devices were not suitable from a dynamic range perspective for use in the HPSDR Mercury. About 90% of the DDC functionality was moved from the AD6620 into the Cyclone II FPGA on the QS1R REV AB prototype. There was not enough room in the FPGA to implement a useful final FIR compensating filter to correct for the passband droop of the CIC filters used in the FPGA implemented DDC. I then investigated using two external FIR filter chips made by a company called QuickFilter Technologies:


Two of these chips were soon grafted on the QS1R board in place of the AD6620 parts for testing. These chips worked very well but I was concerned about their availability. I made a decision at that point to “bite the bullet” and wrote a one-tap-per-clock FIR filter in Verilog to move all of the DDC functionality into the FPGA. I was easily able to fit two 256 tap FIR filters into the remaining space in the Cyclone II FPGA which eliminated the need for the external QuickFilter FIR chips. During this time Altera also announced the availability of the Cyclone III FPGA in a QFP240 package with enough logical elements and hardware multipliers to be very interesting to SDR work – this also prompted me to develop the one-tap-per-clock FIR filter in Verilog since space would no longer be a concern with this FPGA.

The QS1R REV AB prototype allowed me to also test a Hittite HMC472 0-31.5 dB attenuator, a Sirenza SBF-4089/5089 RF Amp, Phil Harman’s 1.5 MHz BPF stage, and a 30/60 MHz LPF stage that is planned to be used in the HPSDR Mercury design.

The Quick Silver was the testing grounds for ideas that will be used in HPDSR Mercury. Without experience gained from the QS1R REV AB prototype, we would have probably ended up with multiple alpha releases of the Mercury as we found these problems later.

Quick Silver QS1RT VERB

During the development and testing of the QS1R REV AB prototype, the Altera Cyclone III FPGA became available in a QFP240 package with enough logical elements to do some interesting SDR work. I wanted to investigate using a PCI or PCIe connection to the PC to allow much wider bandwidths to be processed than the USB 2.0 interface would allow. This is how QS1RT VERB came about. The VERB contains both the LTC2208 ADC and a TxDAC with a fiber optic or copper connection to a PCI/PCIe board in a PC. The high speed serial interface between the QS1RT and the PCI/PCIe card in the PC is made by a TI TLK2711 Serializer/Deserializer chip that transfers at 2.5 GbPS:


As of October 2007, I am in the process of testing the PCI end of the interface. This board uses some expensive components and is only really meant to be a demonstration of a high speed interface and for experimentation. I want to investigate the ultimate achievable bandwidth to the PC from the VERB and also configuration of the FPGA over the high speed fiber optic link.

Quick Silver QS1R REVB

Taking what I learned from QS1R REV AB prototype and QS1RT VERB, I set about designing a third (and hopefully final!) iteration of the Quick Silver board in October 2007. In previous boards, the RF section of the PCB was routed by hand and the digital sections were done by an auto router. In QS1R REVB, all routing was done by hand to optimize trace lengths and minimize vias in the digital sections of the circuit. The board was simplified with applications such as a HF receiver, VNA, spectrum analyzer, and digital oscilloscope in mind:



Included on the board is a 192 kSPS Stereo DAC for audio output. There are provisions to allow an expansion BPF/RF AMP/Attenuator board, an on-board 55 MHz LPF, a direct ADC input connector that bypasses the LPF, an I2C control bus, etc… See the schematic above for details.

The QS1R REV B PCB is completed, assembled, and now undergoing testing as of October 30, 2007.

Wednesday, August 15, 2007

Friday, July 20, 2007


(Click on picture above to see larger version)

Boards were received 07-20-2004

Thursday, July 12, 2007


QS1RT VERB (VErsatile Radio Board) Project:

(Click on picture above for a larger version)

ADC: Linear Technology LTC2208
DAC: Analog Devices AD9744
FPGA: Altera EP3C25-QFP240 Cyclone III
CPLD: Altera EMP240-QFP100 MAX II
USB: Cypress CY7C68013A FX2
EEPROM: Microchip 24C128

  • Internal encode clock is 125 MHz.
  • Board interface is through:
    1. USB 2.0 or,
    2. Optic Fiber SFP Module at 2.5 Gbps or,
    3. Copper Cat6 cable at 2.5 Gbps.
  • TI CODEC provides 48/96kHz audio in and audio out
  • FPGA can be programmed via USB or Fiber/Copper interface in Fast Parallel Programming mode (byte wide transfers per clock cycle).
  • JTAG interface for FPGA and CPLD
  • Connectors:
    • ADC IN
    • DAC OUT
    • MIC IN
    • L&R LINE IN
    • L&R LINE OUT
    • JTAG
    • USB 2.0
    • RJ45 (2.5 Gbps serial over copper)
    • SFP (2.5 Gbps serial over fiber)
    • TTL Level Serial from FX2
    • SPI and I2C to RF external RF board
Status: Prototype boards are scheduled to arrive from PCB manufacturer on July 19th.

RF Front End/BPF Board:
An external RF board will determine the frequency range and will allow home-brew RF front ends. The QS1RT VERB provides an SPI and I2C bus for controlling the RF front end board.

2.5 Gbps Serial Link:
The other end of the 2.5 Gbps interface will be a PCI and PCI Express board for the PC. This interface board will have a matching TI TLK2701 SERDES, a CYCLONE II EP3C25, a TI CODEC, and a PLX PCI or PCIe-to-local bus interface chip. The two boards can be connected by Cat6 copper or optical fiber through the SFP module interface.

The USB 2.0 interface allows the use of the QS1RT VERB with PC laptops or if the copper/fiber interface is not desired.

The ADC IN and DAC OUT ports are transformer coupled using Minicircuits T1-6T transformers which gives 15 kHz to 300 MHz coverage. The external RF front end board will determine the actual frequency coverage of the system.

I am having good luck with Picolight SFP modules for the fiber interface which cost about $50 each. I have successfully tested the optical interface though 100 meters of fiber.

Wednesday, June 27, 2007

QS1RT Prototype 06272007


Please click on the image to see a larger version.

Tuesday, June 19, 2007

TI PCM4222 ADC Now Available


TI's 24 bit, 216 kHz, 2 channel ADC is now available. 122 dB dynamic range is claimed. The part comes in a 48 pin TQFP package. It is available from Digi-Key in single quantities at $22.42 each.

Here is the link: PCM4222

This is a FFT plot of the PCM4222 at 192 kHz with no input:

The rise in amplitude at about 65 kHz is a concern, but for SDR use a bandwidth of 130 kHz would still be useful.

The PCM4222 is definitely easier to get in single quantities for experimenters than the AKM AK5394 is, but the AKM chip is still probably the winner.

Wednesday, February 28, 2007

Quickfilter QF1D512


Here is a link to useful FIR engine chip:


They offer a DIP version for experimentation:


Mouser stocks the parts.


The current status is that I am working on integrating the QF1D512 part into the QS1R receiver prototype. I have no new projected availability for QS1R. In fact it appears that interest may be somewhat limited - enough so that it would not be worthwhile to offer assembled units. In that case the design files will be posted from anyone who wants to build a board.

Wednesday, January 03, 2007

QS1R Block Diagrams & Software news

QS1R Diagrams Posted:

Architecture -
PDF diagram of QS1R overall architecture

RF Front End -
PDF diagram of QS1R RF Front End

Supporting Software:

QS1R/QS1T supporting software will be an open source application called QSRunner. It will support both Windows and Linux. In addition to supporting QS1R/QS1T, QSRunner will also support the SoftRock and HPSDR JANUS-OZY/MERCURY projects.

Sunday, December 31, 2006

QuickSilver QS1R Software Defined Receiver Prototype

QS1R Software Defined Receiver:

(Click on picture above for larger version.)


16 bit 130 MSPS ADC
HPF, LPF, RF AMP Switchable Front End
0-31.5 dB Attenuator in 0.5 dB steps
Cyclone II FPGA
Two AD6620 DDC co-processors
USB 2.0 480 Mbps High Speed Interface to PC
0.1 to 33 MHz coverage (0.1 to 65 MHz extended)
RX bandwidths from 33 MHz to 1kHz
Two independent RX channels anywhere in 0.1 to 33 MHz
6.00" X 4.00" board size
Single +12V 1A supply
Open Source Software and Hardware


Projected late January to mid-February 2007

Saturday, December 16, 2006

vSound Update

vSound Status

I have been able to get a prototype of the vSound driver to work on Windows Vista beta. I am now waiting until the official release of Vista to continue development on a driver that will work on both XP and Vista. As it looks now, vSound will support Vista and XP only. There will be no support for W2K, NT4, or Win9X/ME operating systems. My main concern is trying to make sure that the vSound driver is compatible with both XP and Vista so I don't have to maintain two different versions based on operating system.

There are a lot of changes being made to driver development under Windows and I have been waiting until it stabilizes a little bit more before releasing a beta driver. My best estimate for availability of vSound beta is early next year after Vista systems hit the streets.

New QuickSilver QS1R Group

Support and discussion group for the new QuickSilver QS1R SDR:

To sign up go Here

Tuesday, December 12, 2006

Some Interesting Links for Decemeber...


DSPLINKS - great for learning DSP interactively

QUCS- circuit simulator for Linux and Windows

LTC SWCAD - circuit simulator for Windows

Cell Processor - the processor that power the PS3

SciLab- open source numerical computation

Maxima - open source computer algebra system

Octave - open source GNU numerical computation

Mono - open source .NET

Coming Soon!

QuickSilver QS1R SDR Receiver/Scope/Spectrum Analyzer Board
  • Based on Linear Technology LTC2208 130 MSPS 16 bit ADC
  • Cyclone II EP2C8 FPGA for DDC processor
  • High Speed USB 2.0 Connectivity
  • Two DDC Co-processors
  • External Clocking capability
  • 6.00" x 4.00" (15.24 x 10.16 cm) board size
  • 0.1-65 MHz
  • Open Source Software

Wednesday, October 25, 2006

A SDR based on some K2 design ideas

Here is a diagram of a SDR that uses ideas from the K2 RF front end and PLL synthesizer:


It would use the K2's RF front end. I would substitute the TUF-1 mixer of the K2 with a switching mixer based on a FST3125 bus switch. The QSD would be at a fixed IF of 5 MHz. The LO for the QSD would be derived from a fixed 20 MHz oscillator divided by 4 to generate the quadrature signals needed to driver the QSD switches. The K2's PLL would be modified by eliminating the variable reference oscillator (resulting in the PLL tuning in 5 kHz steps) and substituting one of the LMX National PLLs for the MC145170 PLL used in the K2 design. The K2's VCO design is good, but I would also eliminate the VCO AGC circuit of the K2.

Tuesday, October 24, 2006

SDR LO Ideas

SDR LO Ideas:

There has been a lot of discussion of using DDS or PLLs for the LO generation for HPSDR and SoftRock like receivers. In the current SoftRock series the LO is generated by a crystal oscillator. The downsides of the above approaches are:

1. DDS: spurs and cost of a decent low jitter/low noise clock source. Some of the 400 and 500 MHz DDS chips are on the expensive side.

2. PLL: phase noise. A scheme using a microwave VCO/PLL and dividing it down into the HF range has been discussed. The latest feeling is that the phase noise reduction even after dividing down is not enough to provide a high performance system. A dual PLL loop approach has been proposed to improve phase noise performance but it is likely to be expensive. There are also PLL/DDS approaches of varying complexity.

3. Xtal: limited frequency agility, you are limited to tuning within the passband of your computer sound card.

There is a forth method that might work for lower cost SDR circuits like the SoftRock. It involves the method used for many years in which a VFO is mixed with a crystal oscillator. It is not hard to make a pretty stable and low noise VFO. The output of the VFO/Xtal oscillator could be fed into a microprocessor (like Microchip PIC18F2455/2550/4455/4550 series) or a FPGA/CPLD. The microprocessor or FPGA/CPLD would count the frequency of the VFO/Xtal oscillator and feed the frequency information to the PC for display in one of the SDR programs like PowerSDR or Rocky. This way you would have an indication of your true operating frequency as well as a real tuning knob that is coupled to the VFO (like a real radio!).

Since there is already a microprocessor or FPGA/CPLD involved in measuring the LO frequency and transmitting that information to the PC, VFO stabilization (like Huff-n-Puff techniques) could be also done in the microprocessor or FPGA/CPLD to tame drift in the VFO. This scheme would also work well for the real sampler with AD7760 I describe in the previous blog or when the ADC is integrated on the QSD board when eliminating the sound card. The frequency information would be transmitted to the PC over USB like the audio stream.

In the case where you would want to use the PC sound card but transmit the frequency of the VFO/Xtal oscillator to the PC, provisions could be made in the USB PIC (or you could use a FTDI chip) to control the bandpass filters also.

Tuesday, October 17, 2006

Possible QSD/ISD Switches/ ADC Idea/Misc

QSD/ISD Switches:

Here is a link the PDF data sheets of analog switches that can be investigated for use in QSD/ISD circuits:


Interesting ADC:

Here is a link to an interesting ADC by Analog Devices:


It is a 24 bit, 2.5 MSPS ADC. Here is the circuit idea:


It uses 1/2 of a QSD (not quadrature sampled) to mix the frequency band of interest down to zero Hz with a bandwidth of something like 250 kHz. The IF would be offset to something like 125 kHz. The ADC samples the 1/2QSD output and results in a real data stream. A FPGA or CPLD mixes the real data stream with a complex NCO to generate a quadrature data stream which is sent over USB to the PC where the remaining processing is done. The advantage is a 1 X LO and no I/Q balance problems. One disadvantage is that your sampling rate should be 4 times the desired bandwidth. For narrow band applications this should be no problem because the AD7760 will sample up to 2.5MSPS. A 500 MSPS rate into the PC should allow a bandwidth of almost +/- 125 kHz from the LO frequency.

Nice SDR Enclosure?

Ken N9VV sent me a link to a cool PC case:


Friday, June 30, 2006

vSound Progress & HPSDR OZY


I thought I'd better post an update to my progress on the vSound virtual sound card driver. I have been looking at the WDF stuff from Microsoft and how it could be supported in the upcoming Vista. There are some considerable issues in writing sound drivers that will work in Vista with the Digital Rights Management (DRM) crap. I am hoping to write the driver so it will work in W2K, XP, and Vista.

I would very much like for the driver to work like jack does in Linux. Some things are not possible in Windows, but I think I can get close to jack's functionality.

I hope to have something together to test in a month or so.


I posted a photo of a almost complete OZY board on the HPSDR Wiki. Testing is going well. See updated info at hpsdr.org

73 de Phil N8VB

Saturday, June 10, 2006

Thursday, May 11, 2006

Small Update

The HPSDR project is progressing nicely. We have a design for the ATLAS backplane that has passed the alpha stage. The JANUS board is close to alpha. The OZY board's schematic has been posted for review and comment.

ATLAS orders are close to 200 boards now.

If you have no idea what I am talking about check out:


Also join the HPSDR mail reflector which is quite active.


is another site you should check out if you are interested in Software Defined Radio.