GPS Stabilised

10 MHz Oscillator



James Miller G3RUH

A unique feature of the Rockwell/Conexant/Navman Jupiter GPS engines is that they have a 10 kHz output, synchronised to GPS time. So, with a few additional components one can phase lock a 10 MHz VCXO to the 10 kHz, and then have a simple low cost frequency standard with surprising performance.

Having developed several systems based on this principle, I am now pleased to offer the design illustrated on this page which incorporates the best results of my experience of the Jupiter GPS engine, phase-locked loops and OCXOs. With careful choice of components, patient sourcing and rational design I have been able to keep the price at level affordable by the small commercial or home laboratory and by serious radio amateurs. Read an independent comparison of several GPSDOs.

The frequency accuracy is of course set by the GPS idiom, and is essentially exact for practical purposes. The stability as given by the Allan Deviation is typically 5x10-12 at τ=10s. That figure is 0.05 Hz at 10 GHz and is a remarkably small value.

The low phase noise from the Axtal AXIOM40 OCXO results in a very clean 'sound' to harmonics in the microwave region, and with a power consumption of 300 mA at 12.5V this GPSDO is suitable for field operation from a car battery.

Other applications include radio beacon synthesisers, harmonic markers, 1 MHz 'comb' generators, downconverters, test equipment external frequency reference, small laboratory frequency standard.

 PHOTO - GPS 10 MHz STD - Inside


Power Input
  Voltage   minimum:      7.5V DC stabilised
            recommended: 12.5V DC stabilised
            maximum:     18.0V DC
  Current   min:  0.3A
            max:  0.5A during OCXO warm up (about 2-3 minutes)
  Connector: Screw terminal block

GPS Receiver
  Rockwell Jupiter TU30-D140-221
  GPS connector: SMA socket
  Socket powered 5V for active antenna (100 mA, with short circuit protection)
  LED shows 1PPS (1 pulse-per-second); synced to UTC when receiver locked

Signal Output
  10 MHz sinewave, AC coupled
  Level: 13 dBm into 50Ω ; 1V RMS
  Connector: BNC
  Option:  Output HCMOS/TTL 5V.  (No cost).
  Option:  Output HCMOS/TTL AC coupled ±2.5V square-wave.   (No cost)
  (Options are alternatives to the regular items).

Data Input/Output
  RS-232 in/out of GPS receiver
  Protocol: NMEA (user changeable to Rockwell binary)
  1PPS on DCD line
  Connector: DE9S

Warm-up Accuracy
  After 30 minutes < 10-10 typical
  After 60 minutes < 10-11 

RMS accuracy (over a 10s period)
  8x10-12 ; that is, 99% of measurements would fall within ±2x10-11  

Stability (Allan deviation) typical
    1s  <  2x10-12         1000s  <  2x10-12
   10s  <  5x10-12        10000s  <  3x10-13
  100s  <  5x10-12          1 day <  5x10-14  

  35 H x 92 D x 150 W mm including mounting flange
  Weight  0.430 kg

- Supplied with 80cm power cable with 6mm spade terminations.
- Full documentation.
- Built, tested and ready to use (that is, not a kit).  Just connect your GPS
  antenna, apply 12V DC power and you're in business.

Update 2017 Nov 08 [Wed]


After 10 years and supply of 550 units, this GPSDO has reached the end of production.

This is because I've no more of the required 'Jupiter' GPS engines.

Adequate spare parts have been retained for service/repair purposes.

My sincerest thanks to everyone for your fantastic support of this product: all the hundreds of customers, and especially manufacturer AXTAL GmbH who, with astounding service, supplied the special AXIOM40 OCXOs.

When I've tidied up the residual contents of my stores, there will be surplus items, which I will offer for sale here.

2019 Jul 15 Surplus Item: GPS Antenna Symmetricom/HP 58532A; ALL SOLD

2019 Nov 25 Surplus Item: Coming soon - AXIOM OCXOs

Frequently asked Questions

Prior GPSDO developments with emphasis on self-construction.

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Last updated: 2020 Jul 05