OCXO 106.5 Mhz or 108Mhz

 

Here is an OCXO 106,5Mhz or 108Mhz more! Why not to have used the already appeared descriptions: they require quite a copper box not easy to realize, this is realized with the material of plumbers.

Results after 2 months of ageing the passage of 23 ° to 3 ° (in the refrigerator) gives a drift of 2 hertzs. Or 0,02PPM. Others measures will be made soon.

Boitier and temperature regulator:

I used as box a brass tube of 26mm inside on which a resistor wire is rolled up around between 2 coats of capton ribbon. The system of temperature regulation use a sensor LM 335 (In thermal contact to the tube) who generates a proportional voltage at the temperature (10mV / degree). A pulse modulator (1/2 LM392) compares the tension of the LM335 with the tension divided of the reference of tention LM336.5. The pulses are amplified up to a BD139 ( saturated regime) which feeds the resistor of 25 ohms rolled up around the tube. Advantages: an uniform distribution of the warmed zone, a "nervous" regulation, a thermic slowness between the tube and the print that can weaken the possible temperature variations of the tube. The tension reference LM336.5 should not be directly solded on the print, but in thermal contact with the tube and connected via flexible wires . This improve the stability of temperature, the tension reference being a little bit sensitive to the thermic variations.

Temperature:

The systeme described here works at 40 degrees and is used with a quartz cut for 20 degrees. If one desire to use it with a quartz cut for 60 degrees, it is necessary to ajust R4 1K and R5 3,3K for increase the tension of 200mV.

Oscillateur:

The oscillator is inspired of a DD9DU'S LO, a varicap was added for tune the frequency after ageing of the quartz, 10 turns of the potentiometer gives 250 Hz at 106Mhz). An attenuator in T follows a buffer with a BF199 then isolate the oscillateur of the load variations. It is realized in SMD resistors (The values of resistors are to calculate according to the wished level). A filter follows to cut the harmonic 2, the harmonics are quite lower in 50dB.

Assembly:

Tube box:

Built in a copper tube of 26mm inside with plumbers caps cut at 9mm. On the front cap, a SMA and a 1 nF bypass are solded, on the back cap drill a hole in front of the axis of the potentiometer (multiturns). A capton adhesive of 8mm large is rolled up in spiral on 5 turns with a space of 1 mm, at the ends fix a isolated contact. Roll up on the capton 5 turns of resistant wire (100 ohms / m ) and weld the extremities on the contact. Cover the wire with a new layer of capton (a drop of 2 components glue can protect wire extremitys). In the center of spiral beetwen 2 turns of wire, drill a small hole for one paker screw which will fix a strap to maintain the sensor LM335. Cut the capton under the sensor and put some thermic grease. The print is maintained by 2 small columns of 10mm.

The connection between the print and the SMA should be made by 2 short supple wires to delete mechanical connection between the cap and the print, the prototype where the print was welded on the cap was less stable.

Heat insulation:

The tube is placed in an insulating foam surrounded in a aluminium sheet.

Oscillateur:

The printed circuit is double face with the superior face as earth plan. Drill shorts 2.5mm holes only on earth plan for the legs component. The coil box will be welded on the earth plan. The quartz box should be welded on the earth plan of the circuit.

In first do not welde the SMD resistors attenuators but make a wire bridge.

Regulation:

Adjust the potentiometer in median position, adjust the coil core to bring the oscillation to the wished frequency, adjust the BF199 circuit for a maximum level. With an spectre analyzer adjust the filter to minimize the harmonic 2, then tune another time of the circuit of the BF199. Measure the level, according to the wished power, calculate the value of the attenuator then take of the bridge and weld the SMD resistors of the attenuator.

If necessary, tune the frequency with the potentiometer.

The resistor wire and all the components of the heater are in the "Conrad" catalog .

REGULATION................OSCILLATOR ...............TUBE PLAN...............COMPONANTS................PhotoOCXO

Good realization and finished the QSY at + or – X kHz.

73 F5AYE

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