Precision Frequency Reference for your Radio

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The XRef series of boards take a 10 MHz reference signal from a GPS reference or other high accuracy source and provide a precision reference frequency.  This eliminates the problem of your radio being off frequency and drifting as it warms up.  If the 10 MHz reference signal is not available, the board reverts to using its onboard TCXO as its source, or optionally reverting to the radio's own internal reference.

Developed jointly by Graham VK3XDK and David VK3HZ, the XRef is designed to be installed in a wide range of Amateur Radio Transceivers, Receivers and SDRs.  Detailed installation instructions are available for a number of popular radios (see links below).

There are three types of XRef:


The XRef-FT is a direct drop-in replacement for the reference board in the Yaesu FT-817, FT-857 and FT-897.  It produces a precision 22.625 MHz reference frequency from an external 10 MHz reference signal.  It also has an onboard TCXO for use when the external 10 MHz is not available.TCXO frequency adjustment is via a 10-turn trimpot.  The XRef-FT is based on a Silicon Labs Si-4133-family synthesiser with an onboard Atmel processor to handle configuration and monitoring.

                                     XRef-FT boards

Fitting the XRef-FT to your radio is a simple process. Remove the top cover, unplug the OEM frequency reference, plug in the XRef-FT and feed in the external reference signal. The Installation Instructions describe the process in detail and, for those who like to keep their radios factory fresh, several methods for bringing in the external reference are suggested that do not require permanent modifications to the radio. 

The fitting instructions can be found here: XRef-FT Installation

Testing has been carried out with an FT-817 fitted with the original (OEM) reference oscillator and then with the XRef-FT. The XRef-FT was operated from its onboard TCXO and from an external 10 MHz reference from the Spectrum Analyser.  The test setup used an HP70000 series Spectrum Analyser driven by the KE5FX Phase Noise measurement utility. 

FT-817 Phase Noise results for 432 MHz (Click for larger image)

The 432 MHz band is the highest band for the FT-817 and so the most likely to be affected by Phase Noise.  To summarise the phase noise plots for that band:
- At 1kHz offset, all oscillators give the same result.
- At 10 KHz offset, the OEM is best at -102 dBc/Hz, XRef/10 MHz about 5 dB worse at -97 dBc/Hz and XRef/TCXO another 5 dB worse at -92 dBc/Hz.
- At 100 kHz offset, they are all back to about the same level.

The results of other tests are stored as GIF image files named according to their contents.  The files are here.

Overall, these appear to be very good results.

** UPDATE - Steve WA9VNJ used an FT-857D fitted with an XRef-FT in the 2014 ARRL Frequency Measurement Test.
On 80m, he achieved a result within 0.01 Hz of the actual frequency, while 40m and 20m were within 0.14 Hz.
Steve said "Great little board. The combination competes well in the FMT with the guys having "instrumentation" setups.
I suspect the Doppler shift due to the ionosphere changing was the biggest source of error [over the 1200km path]"


The XRef-Versatile is a more general add-in 10 MHz-locked reference board, suitable for most other radios.

There are two versions of the board:

- the XRef-VT has an onboard TCXO. It is intended for radios that have a mediocre reference oscillator like the FT-847 or IC-706.

- the XRef-VS doesn't have the TCXO but instead has onboard power switching to control the radio's own reference oscillator. It can be used for radios that already have  a good-quality internal reference. With this version, when the 10 MHz external reference is not present, the radio's own internal oscillator is enabled.

Testing of a prototype XRef-VS board has been carried out on an Icom IC-910H.  The radio is fitted with the optional Icom CR-293 High-Stability Reference Oscillator (referred to as "OEM" in the Phase Noise plots.  Tests were done on the highest band - 1296 MHz.

IC-910H (with CR-293) Phase Noise results for 1296 MHz (Click for larger image)

Fitting of the XRef-Versatile to a radio will most likely require some soldering and perhaps cutting of tracks.  The board is small enough (approx 13mm x 32mm) to fit inside most radios, with only a 10 MHz connector on the rear panel.

The following table lists the recommended XRef version for each of the currently supported radios and a link to the Installation Guidelines:

Radio XRef-VT
Icom IC-706MkIIG
Icom IC-910H (1)
Kenwood TS-2000
Yaesu FT-847
(1) If the Hi-Stab CR-293 Option is fitted, then VS.  Otherwise either.

The board is capable of generating frequencies from about 15MHz upwards and so should be compatible with most radios.
To date, with our guidance, people have fitted them to radios as varied as the Yaesu FT-100D and FT-736R, Icom IC-7400, Kenwood TS-440 and even an SRL QS1R and SDR-IQ.
If you have another model of radio and want to discuss whether the board will suit it, please contact us by email at the address given below.


A number of recent Amateur transceivers (notably Icom) use a voltage-controlled Reference Oscillator, allowing front panel adjustment of the Reference frequency.
The XRef-PLL locks the radio’s Reference Oscillator to an external 10 MHz reference signal from a GPS reference or other high-accuracy source.
It intended to be installed internally within the radio.  When no 10 MHz reference is connected, the XRef-PLL disconnects from the radio, allowing it to operate as from the factory.

The following table lists radios for which Installation Guidelines are available:

Radio Reference Freq
Icom IC-9100
32 MHz

The board is capable of generating other frequencies and so should be suitable for many radios with a voltage-controlled Reference oscillator. 
The main restriction is gaining access to the radio's internal circuitry to connect the XRef-PLL - some radios have extensive shielding covering this area.

If you have another model of radio and want to discuss whether the board will suit it, please contact us by email at the address given below.


Price ($AUD)
XRef-FTFor Yaesu FT-817, FT-857 and FT-897Not Available
XRef-VTVersatile version with onboard TCXONot Available
XRef-VSVersatile version with switchingNot Available
PLL version
Not Available

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Contact Details

 For all enquries, contact David Smith at 

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