This is the QS1R FAQ

Q1. Where can I find the QS1R software?

A1. The latest official release of the QS1R software is always available at the following address:

Q2. Where can I find the QS1R schematics?

A2. If you are a QS1R owner, you can request a copy of the schematic for your unit via email. Please include the serial number of your unit and the name it was purchased under.

Q3. Can I get the schematic if I don't have a QS1R?

A3. The schematic for the QS1R is available by request to QS1R owners only. The QS1R PCB production files are not being released at this time. The QS1R receiver is a commercial product, so the research and development costs must be recovered to fund future development as well as underwriting the continued software development.

Q4. How long after ordering a QS1R receiver can I expect to receive it?

A4. QS1R receivers typically ship within 3 business days after order.

Q5. Where can I order a QS1R Receiver?

A5. You can order the QS1R from the website: <>

Q6. How do I correct the frequency offset in SDRMAX V?

A6. SDRMAX V allows you to make the clock correction directly in the GUI and this is the preferred method. In the SDRMAX V GUI click the "SET" button to open the QS1R settings window. In the Clock Correction box, adjust the clock correction value in Hz to calibrate your QS1R. Please refer to this video:

Q7. What software is available for the QS1R Receiver?

A7. The newest software for the QS1R is SDRMAX V which is under active development.

QS1R also will work with Winrad or its variants like HDSDR.

Q8. How can I use QS1R RevD in under-sampling applications?

A8. You must bypass the on board LPF and supply your own external bandpass filtering. To bypass the LPF on the QS1R RevD, remove C67 and either place 0.1uF 0603 caps or zero ohm jumpers in C68 and C64 positions.

Q9. How can I use the QS1R RevD with an external encode clock?

A9. To use the external encode option, disable oscillator U9 by placing a zero ohm jumper at J5. Place a zero ohm jumper at J26 to enable the external clock input. Supply a 0 to 130 MHz clock to J1. The external clock can be sinewave or squarewave drive, 3.3 V pk-pk maximum.

Q10. Where can I download SDRMAX V?

A10. The installer for the latest release of SDRMAX V is always at:

Q11. What is the software for the QS1R called?

A11. The next version of the software is called SDRMAX V. Binaries will be available for Windows XP/VIsta/7, Linux, and MAC OSX. It is available for download at

Q12. What is the pinout for the QS1R RevD Mini DIN connector?

A12. The pinout is as follows:

1 - I2C SDA
2 - I2C SCL
3 - +3.3VD
4 - GPIO2
5 - GND
6 - GPIO3
7 - GPIO1
8 - GPIO0

Q13. Will I be able to use my QS1R RevC or RevC1 board with the Mini DIN connector that now is supplied on the QS1R RevD board?

A13. Yes. Depending on demand, a small PCB will be made available with the Mini DIN connector mounted that will add this connector the existing QS1R RevC and RevC1 boards.

Q14. How do I install the QS1R driver?

A14. The installer for SDRMAX V includes the driver installation. At the end of the installation dialog for SDRMAX V, you will have the option to install the QS1R driver.

Q16. I am having trouble running Skimmer Server and QS1RServer at the same time.

A16. You can not run both programs at the same time.

Q17. What is the maximum safe input to the QS1R's RF IN connector?

A17. You should not exceed ~3V pk-pk into 50 ohms. That is about 20 mW or 13 dBm.

Q19. What power source does the QS1R require?

A19. The QS1R requires 5-6 VDC @ 1000 mA when running SDRMAX software. When running CW Skimmer Server, the QS1R requires 5-6 VDC @ 2000 mA. The coaxial power jack is 2.1mm center pin positive. A 2.1mm or a 2.5mm center positive power plug will work.

Q20. Do you have a recommendation for a power supply for the QS1R?

A20. You can order either a USA (120 VAC, 60Hz only) or Universal (90-264 VAC 50/60Hz) power supply from the SRL-LLC website. You should order the Universal power supply if you intend to run Skimmer Server with the QS1R because this power supply is rated at 2000 mA.

Q21. What is included when I purchase the QS1R?

A21. The QS1R Receiver includes an aluminum enclosure and filtered USB cable. The power supply can be purchased separately or the user can supply his/her own power supply. Two power supplies are available for purchase - a USA 120 VAC. 60 Hz input supply and a Universal 90-264 VAC, 50/60 Hz input power supply. The Universal power supply includes interchangeable blades to work with most countries power systems.

Q22. How do I protect the QS1R front end when using it with a transmitter or transceiver?

A22. See question Q17 above. The most effective way to protect the QS1R is to short the RF IN on transmit with a relay. The relay should provide enough isolation to limit the RF input to the QS1R below 20 mW or 13 dBm.

Q24. How do I use the QS1RServer without the SDRMAXII GUI?

A24. The QS1R can be operated without the SDRMAXII GUI via the command line in the QS1RServer application. You can start the QS1RServer by running QS1RServer.exe in the /SDRMAXII/ServerFiles folder. When QS1RServer is started and ready it will appear as so:


To get to the QS1RServer menu type "m" on your keyboard and hit the enter key. The QS1RServer Commands menu should look like:


Typing the following commands followed by enter on the keyboard will perform the following functions:

1 - will start the server

2 - will stop the server

a - sets/reports the AGC mode (off, long, slow, med, fast)

f - sets/reports the frequency

h - sets/reports the filter upper (High) limit in Hz.

l - sets/reports the filter lower limit in Hz.

m - sets/reports the current mode (AM, SAM, LSB, USB, etc...)

q - mutes the audio

r - reports the QS1RServers current settings.

t - sets/reports the current AGC threshold

u - increases the receive frequency by 500 Hz

d - decreases the receive frequency by 500 Hz.

v - sets/reports the volume

x - exits the server

Q25. Do you have a suggested circuit for QS1R front end protection in a multi-transmitter environment?

A25. In a multi-transmitter environment it is not always practical to protect the QS1R front end with a shorting relay. The following link is a schematic of a suggested front end protection circuit that is similar to what is used in a commercially available device:

Here is a candidate for the incandescent lamp: GF550 It fits into a fuse holder, such as this one, for easy replacement.

Capacitor C1 in the schematic can be reduced to 0.1uF and C2 to 0.01uF. The capacitor's working voltage should be 50 V or greater. Their ratio should be kept at around 10:1 whichever values your choose. The lamp I1, should be rated at 6-6.3 V and 100 - 200 mA. I do not recommend substituting other diodes for the 1N4148 diodes.

The lamp I1 limits the current through the back to back 1N4148 diodes. As the diodes begin to conduct and shunt the RF input to ground, the increasing current through lamp I1 causes the lamp's resistance to increase - limiting the current through the diodes and preventing them from burning up. At some level of RF input, the lamp's filament will open acting as a fuse. That is why you might want to consider making lamp I1 easily replaceable.

Note that this circuit will degrade the QS1R specs since at some level of RF input the signal begins to clip - this will occur before you reach the +10 dBm clipping limit of the ADC. For many users, this will be an acceptable trade-off.

Q26. How can I tell if my current PC and CPU is powerful enough for SDR applications?

A26. Here is a great free utility that will give you all the information you could ever want about your system: If you download and install cpu-z and then run it, go to the "About" tab and you can save the report as a text file ("Save Report (.TXT)). Please email (p<dot>covington<at>gmail<dot>com) this text file to me and I will be able to give you a better idea about whether your system is powerful enough to run certain SDR applications such as SDRMAX, Skimmer Server, PowerSDR, etc...

Here's a screen shot of cpu-z:


Also, check out their other utilities like

Q27. Does QS1R work with Winrad or its variants?

A27. Yes. You can use the QS1R with Winrad by installing the QS1R ExtIO support files. Sampling rates up to 2.5 MSPS with a bandwidth of 2 MHz is supported. Here is a screen shot of Winrad running with the QS1R at a sampling rate of 2.5 MSPS showing 2 MHz of bandwidth in the AM Broadcast band.

Q28. How do I bypass the QS1R internal low-pass filter (LPF)?

A28. To bypass the low-pass filter (LPF) you need to place either zero ohm jumpers or 0.1uF chip capacitors at positions C64 and C68 on the QS1R board. In addition you need to remove C67 and C69. Zero ohm jumpers ( shorts ) are recommended for positions C64 and C68. An example of a 0603 zero ohm jumper is DigiKey P/N: P0.0GCT-ND. If you are not confident you can perform this modification yourself, this modification can be done at the factory. Please contact SRL-LLC for details.

Q29. How do I use the QS1R as a 75 MHz IF?

A29. Please see Q28 above to bypass the low-pass filter on the QS1R. You may have to add an external band-pass filter for your 75 MHz IF. A suggestion might be Minicircuits filter <> The 75 MHz IF will show up at a QS1R tuned frequency of 50 MHz (62.5 - 75 = -12.5 MHz or 50 MHz ( 62.5 - 12.5 ). Using the frequency offsetting and correction features of the SDRMAX software, you can then make SDRMAX display 75 MHz instead of 50 MHz.

Q30. What is the part number for F1, the 2 A protective fuse and D1, the protective diode on the QS1R board?

A30. Fuse F1 part number is Digikey P/N P11374CT-ND. Diode D1 is Digikey P/N DDZ6V8CSDICT-ND.

Q31. Can I connect the QS1R to my PC through a USB hub?

A31. It would be best to avoid using a USB hub if at all possible. It is better to connect the QS1R directly to your motherboard's USB ports. If you have run out of USB ports, you can add a hub to move all of your low speed devices, like mice, keyboards, printers, to to free up the main motherboard USB ports.

Q32. How do I hardware mute the QS1R DAC audio output?

A32. The QS1R uses GPIO0 for the hardware mute input. This is pin 8 on the MiniDIN IO connector on the back of the QS1R. Grounding this pin will mute the DAC output. See the MiniDIN pinout for pin 8. See FAQ Q12 above for the MiniDIN pin assignments.

Q33. What ports should I open in my firewall for the SDRMAX(x) software?

A33. SDRMAX(x) uses ports 43065 through 43075.

Q34. What language and compiler is used to develop the latest SDRMAX V software?

A34. SDRMAX V is written in C++ using Nokia's open source Qt5 toolkit. The released Windows binaries are compiled with msvc2010. You can also compile the SDRMAXIV GUI on Linux and OS X currently.

Q35. Is SDRMAX V open source?

A35. No. You can get access to the source code by requesting and signing a NDA document with Software Radio Laboratory LLC.

Q36. Which driver does SDRMAX V use for communication with the QS1R via USB?

A36. SDRMAXIV uses the libusb-win32 driver.

Q37. How can the QS1R be used to receive frequencies above 62 MHz?

A37. The QS1R encode clock is 125 MHZ. It will receive from 10 kHz to 62.5 MHz.

The closer you want to use it to 62.5 MHz, the more stop-band attenuation your low pass filter needs to prevent frequencies above 62.5 MHz from aliasing down into the 0 - 62.5MHz range.

Band 0: 0 - 62.5 MHz


Band 1: 62.5 - 125 MHz
Band 2: 125 - 187.5 MHz
Band 3: 187.5 - 250 MHz
Band 4: 250 - 312.5 MHz
Band 5: 312.5 - 375 MHz
Band 6: 375 - 437.5 MHz
Band 7: 437.5 - 500 MHz

You want to avoid multiples of 1/2 the encode clock frequency. The closer you get to the edges of the above bands, the more filter stop-band attenuation you will need to prevent aliases.

For Band 0, a 50 MHz low pass filter is adequate.

For Band 1 and higher, you will need bandpass filters, not high pass filters (or a combo of a LPF and HPF). The QS1R ADC will respond to frequencies up to 700 MHz, so you need to filter out the higher frequency end also.

To switch back and forth you should completely bypass the internal LPF on the QS1R.

You can check out Minicircuits which have a large selection of bandpass and low pass filters in various frequency ranges. You could also build custom filters from discrete components like Coilcraft inductors and NPO capacitors.

You can manually switch the filters or use a relay or electronic switch such as those available for RFMD. The QS1R has an I2C bus output and also some general purpose IO lines that can be used to switch the filters.

For VHF/UHF use you probably want to use a low noise preamp. Minicircuits have many MMICs that will do that for you, or you could purchase a ready made preamp.

Lots of possibilities for the experimenter/hobbyist...

Q38. How can I change the default wav file recording path in SDRMAX V?

A38. You can set the record path to where ever you want. By default it is in your user folder in the "SDRMAX V Recordings" subfolder. To change the path you must edit the SDRMAXV 5.0.0.X.ini configuration file. On Windows 7, this is located in your user folder in the "AppData/Roaming/SRL-LLC" folder. For example, if my user name is "phil" then it is located in C:\Users\phil\AppData\Roaming\SRL-LLC\. You can edit the SDRMAXV 5.0.0.X.ini file with notepad.

Add this entry:

WAVRECPATH="F:/My Desired Record Path/"

Then start the server. Recordings will be made to this path.

Q39. How can I set the USB device permissions for a local user for my QS1R in Ubuntu linux?

A39. You need to create a udev rules file.

Run the following commands:
sudo <your favorite editor here> /etc/udev/rules.d/50-qs1r.rules
In this file put the following four lines. Note: YOUR UNIX USERNAME HERE is ...your unix username.
SUBSYSTEM !="usb_device",ACTION !="add",GOTO="qs1r_rules_end"
Save the file and exit your editor. Reboot your system and you should now be able to start the server as a local user without root permissions.

Q40. Is the QS1R Receiver FCC Part 15 and CE Conformant?

A40. Yes. Please see the QS1R Online Manual section 2.0 for conformity statement.