Low cost, 10MHz high stability frequency reference for radio applications. (OCXO)Designed by ZachTek in Sweden
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What is it? It's a 10 MHz quartz square wave generator with an oven controlled crystal for high stability. It's typical applications is as a reference for synthesizers. It contains a Japan made OCXO …Read More…
It's a 10 MHz quartz square wave generator with an oven controlled crystal for high stability. It's typical applications is as a reference for synthesizers. It contains a Japan made OCXO module that has been used in another product before being recycled, put in to this design, tested and trimmed by me. This mean you can have a very high quality frequency reference at a fraction of the price you would have paid if you used a new OCXO. Special attention has been made to ensure high stability and low noise even at varying power supply and load conditions which makes it ideal as a bench reference to be used whenever a stable 10MHz frequency reference is needed.
I needed a good, stable frequency source for my synthesizers and to be able to plug it in and out of circuits while still retaining it's set frequency.
I designed it to minimize frequency variations due to varying load and Power supply conditions. I also paid special attention to minimize power supply noise feedtrough. As a consequence this design have three voltage regulators, two of them are very low noise LDO that are specialized for synthesizer applications. Furthermore the output is isolated from load variations that would otherwise affect the frequency stability. This isolation is by menas of amplification followed by attentator. The attenuator makes the Oscillator "see" 50ohms impedance even if the output is miss-matched by the external load. All these design features ensures the highest stability and lowest noise 10MHz source while still keeping it affordable.
It needs minimum 7,5V DC. If you feed it with more than 8-9V you need to attach a heatsink to the 7806 Voltage regulator to cope with the power dissipated. The case of the 7806 is at ground so it can be screwed directly to the side of a metal case without the need to isolate it. It uses about 600mA of current for the first minutes when the oven heats up the crystal to its operating temperature. It then stabilizes at about 300mA. The output level is 14dBm square wave in 50ohm. Measured in Volts that is 0 to 6V if not loaded and 0 to 3V if loaded at 50ohm.
There is a Voltage control Input that enables adjustment of the device +/-15Hz. The voltage that gives exactly 10MHz differs from device to device but is generally somewhere around 1.2 to 1.8 Volts. This Input is normally connected to a 30-turn trimmer feed by a 3,1V ultra-low-noise voltage regulator. I have adjusted it using a GPS derived comparison frequency so it is exactly 10,000,000.0 Hz. By moving the jumper one can get control over the voltage trim input and the 10MHz out to the IDC connector. This makes it possible to use the oscillator in a PLL project for example to GPS discipline it.
Catalin | March 11, 2018
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