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  • GPS-Locked Precision Frequency Reference | Low-Jitter GPS Clock 450-Hz to 800-MHz Output - front view
  • GPS-Locked Precision Frequency Reference - rear view
  • Its small! Just 4" x 2" x 1" including connector protrusion
  • Says product designer Leo Bodnar: "The phase noise is so good i have problems measuring it.  I had to buy 14-bit version of E4406A to measure it and had to filter out the carrier with a sharp notch filter at 12-MHz. 10-MHz noise is the same as 12-MHz on this image (blue trace)....Noise above 100-kHz is better than stated as it is drowning in E4406A noise floor and 220-kHz spurious is (from memory) an E4406A artifact as well. Measuring such a low phase noise is black art and a bit academic so I did not pursue it further."
  • Connect the device to a PC via the supplied USB cable and program wtih this free app available from www.leobodnar.com

GPSDO Precision Frequency Reference | 450 Hz to 800 MHz GPS Locked | Low-Jitter Clock | Leo Bodnar Electronics

$ 249.00

Product Description

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Great for adding ultra-high accuracy and stability to any two SDR (FlexRadio, QS1R, Elecraft, Apache Labs, et al), transverter (Kuhne, DEMI, et al), propagation beacon or other devices

Ultra-accurate - don't be fooled by the low price!

QST review here (courtesty ARRL)

Oh doode this thing rocks.

At first I had a little trouble when I plugged it into a powered USB hub I use for a lot of other stuff.  Once I plugged it into it's own USB port on my PC it was super simple to set it up for 120MHz output AND 10MHz output.
I'm using the 10MHz to clock my Airspy, and HackRF, and Apache Labs "Hermes" board. Through a little 10MHz distribution (it's a 4 port splitter with one port terminated with 50ohm load) I'd do better to get a 3 port splitter but this has always worked, and seems to still be working.
Nice thing about this unit is that it sync's up with GPS in < 1 min. And gets PLL lock pretty quickly.
My old Jackson Labs "Fury" which is a 10 MHz GPSDO is very good, but can take a VERY long time to do a 'survery' and get stable lock from cold start. Which really doesn't matter since it ran all the time anyway. But it was a pain in the butt when I had to power it down and back up, and wait.
...I'm REALLY excited about this. I've been searching for an affordable device like this Clock Ref, for years! Prior to this, I'd even built my own 100Mhz OCXO upconverter trying to resolve upconversion drift issues.
This new device should make life with SDR's MUCH simpler, I think.  It's really exciting. I've spent a ton of money and time on resolving SDR drift issues in the past 3-4 years. This basically solves itwithin 5 minutes of the box arriving in the mail box.
VERY COOL! I'm happy :-)  -Tim, NW0W

Force 12 CEO Bill Hein was Googling for a low cost but ultra-accurate frequency reference for the SDR receiver he uses at the RBN (Reverse Beacon Network) node that operates 24/7/365 under the W0LFA callsign at his Glade Park, Colorado station and came across Leo Bodnar Electronics.

Leo Bodnar is a designer and developer of force feedback simulator steering systems and related products and technologies. Based in Silverstone, England - the home of British Motorsport - has enabled Leo to work closely with and meet the demanding requirements of professional race teams, drivers and simulator manufacturers using high quality and reliable components to ensure they meet the highest levels of performance and reliability. Leo is also a ham (M0XER) so it's no surprise that his GPS-Locked Precision Frequency Reference has applications in the ham as well as the professional world.

Bill ended up not just buying a unit for his station but also obtained American distribution rights and the Force 12 Superstore. Bill believes that the unit has numerous ham shack applications such as providing a highly-accurate reference to SDR radios, transverters and anything else that needs to be ultra-stable and dead on frequency.

The tiny device outputs two synchronised low-jitter reference clocks locked to GPS. Long-term stability of the output signal is defined by the high accuracy GPS caesium references and theoretically approaches 1x10E12. Short term signal quality is defined by the internal TCXO clock source providing a high-quality, low phase noise clock signal with sub-picosecond RMS jitter (that's pico, not nano!)

The digital PLL allows output reference frequencies to have almost any value between 450-Hz and 800-MHz. The two outputs can be individually enabled and set to different frequencies almost anywhere within 450-Hz to 800-MHz. If both outputs have the same frequency their relative phase shift can be adjusted. This can be used, for example, to generate two signals with 90° phase shift for use in an I/Q mixer. Note: there are limitations to the frequency which the second oscillator can be set based on the frequency of the first oscillator so best to think of the second oscillator as a bonus and not a guaranteed feature. If you have a particular frequency combo you want to use, please get in touch with us and we'll run the numbers.

Both square wave output signals are at 3.3-V CMOS levels with 50-Ohms characteristic impedance. Output drive levels can be adjusted from +7 to +13.3dBm. The output level must be the same for each output.

Operation requires continuous presence of GPS signal. Active or passive GPS antennas are supported. An active antenna with 3 metre cable and SMA male connector is available from Force 12 Superstore as an option.

GPS acquisition time after power-up is 30 seconds. If GPS signal is lost, digital PLL maintains best estimated output frequency based on historical data. On reacquisition of GPS lock, output is seamlessly brought back in sync with GPS reference. Entry and exit of frequency hold is glitch-less.

All frequency and output settings are fully user-configurable via USB connection from Windows PC running Windows OS versions (TBD).

GPS clock can be powered via USB input or from external 5-15-VDC power input. USB connection is used for configuration and is not required for operation.

Uses include:

  • Reference for amateur radio equipment, SDR rigs, transverters, propagation beacons, frequency markers
  • Helps advanced digital mode operation with frequency accuracy and stablity are paramount (WSJT, WSPR, et al)
  • 10.000-MHz, 1.000-MHz or other frequency reference for lab equipment and instrumentation
  • Reference for receiving equipment such as RTL SDRs (28.8-MHz) and band scanners
  • Calibration source for radio receivers
  • Master clock for audio and video equipment, DACs and studio recording gear


  • FlexRadio Systems 
  • QS1R SDR (requires internal jumper change)
  • Elecraft K3 and K3S transceivers (requires Elecraft K3EXREF option)
  • Apache Labs ANAN Series SDR transceivers (requires FPGA setting change in ANAN-200D, internal jumper change in other models)
  • Others?

Measured phase noise of standard (TCXO) version is equal to or better than:

  • -120dBc/Hz at 100-Hz
  • -133dBc/Hz at 1-kHz
  • -137dBc/Hz at 10-kHz
  • -140dBc/Hz at 100-kHz
  • -144dBc/Hz at 1-MHz

Designer Leo Bodnar said about the device's phase noise: The phase noise is so good I have problems measuring it.  I had to buy 14-bit version of E4406A to measure it and had to filter out the carrier with a sharp notch filter at 12MHz. 10MHz noise is the same as 12MHz on this image (blue trace - see photo gallery on this product page). Noise above 100kHz is better than stated as it is drowning in E4406A noise floor and 220kHz spurious is (from memory) an E4406A artefact as well. Measuring such a low phase noise is black art and a bit academic so I did not pursue it further."

Measured 60-MHz GPS clock power output on a well calibrated Agilent E4406A signal analyser:
  • 32mA drive: +13.3dBm
  • 24mA drive: +12.7dBm
  • 16mA drive: +11.4dBm
  • 8mA drive: +7.7dBm

We also stock a version based on a crystal that exhibits even lower phase noise (which is already very, very low), more info here.

We are happy to advise whether specific combination of output frequencies are achievable and preset them into the product before shipping.

Consumed current from +13.8-VDC supply with standard GPS active antenna and two outputs connected to 50-Ohm loads is 130mA.

Comes with standard 2.1mm coaxial power plug and pigtail cable (also can be powered its USB port). USB cable used for device set-up only, after programming will run without PC connection. GPS antenna and USB cable (USB A to USB B connectors) sold separately, device supplies 3.3-VDC @ 100ma to active GPS antenna via SMA connector.

Its small! Just 4" x 2" x 1" including connector protrusion (see photos).

We now have in stock a TomTom Active GPS Antenna with magnetic base, 197" cable and SMA male connector that works well with the Bodnar GPSDO. Sold separately. Info and order here.

Free PC Software for the Bodnar GPS Clock downloadable here

QS1R info, see Q & A #9 here:


Shipping in the USA is free (usually via USPS Priority Mail), for International orders we will bill you separately for delivery via your choice of carrier.

Usually ships same or next business day from Force 12 Superstore Colorado warehouse
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