High stablility crystal oven based on the principle of zero temperature gradient

High Stability Crystal Oven based on the Principle of Zero Temperature Gradient

By Rex Moncur, VK7MO

Karlquist et al1of Hewlett Packard, discussed the theory of Zero Temperature Gradient crystal ovens that can produce improvements in frequency stability with temperature by a factor of 20 or more compared to conventional oven oscillators. The techniques used by Karlquist lead one to think about what might be possible with amateur home brew construction. This has led to the concept of a modified Zero Temperature Gradient oven based on a conventional oven in conjunction with six low-cost DB6NT precision crystal heaters that actively maintain a zero temperature gradient within a diecast box.  The modified Zero Temperature Gradient Oven has a stability* of better than 1 Hz at 1296 MHz, or one part in 10^9th.

* Stability measured in the home environment over 24 hours with ambient temperature variations of 5 degrees.

Installation of a QH 40 A crystal heater into a standard JRC JST-245 TCVR

Here are some photos of my installation of the QH40A crystal heater into a standard JRC JST-245 tcvr. The 12 V DC and ground supply are right next to the std oscillator crystal and DC voltage is present when tcvr is switched on. I do have a TXCO for the JST-245 [not installed]  but instead I fitted your QH40A, I did not need to remove the synthesiser pcb to enable me to fit the QH40A , it can be fitted without removal of any parts or pcbs. I know some amateurs use the JST-245 as a transverter driver for 2m contesting and EME. I use mine on 50mhz for EME, this morning at 0430z I worked ZL3TY  via EME on 6m using JT65A  mode, with the JST-245 as my transmitter.

QRA  RE57OM > IO91DO = 18,862KM .


Ian Williams M0BCG

Installation of a QH 40 A crystal heater into a Icom IC-746


Here are the photos I made for installing properly the QH40A in my Icom
IC-746, using an internal 8V line given by a 7808 regulator in the
tranceiver as supply for the QH40A.

For better thermal stability I used silicon compound between the
reference XTAL and the heater, and I placed cotton arround the
oscillator as showned on the photos..

The mesure I did with my Marconni 2955 (OCXO) Radiocom test set and
Racal Danal 1991 (TCXO) frequency meter give 50Hz drift on 145.000 MHz
when transmitting continuously 5 minutes after 4 hours standing on
receiving (to get the tranceiver warm up).

This give frequency stability better than +/- 0.2 ppm ... and better
than the Icom CR-282 TCXO solution wich is +/- 0.5 ppm.

Best reguards, Gerald - F4AVW.

QH40A Mod for FT-847

QH40A Mod for FT-847

Despite my fan modifications, I was not quite satisfied with the frequency stability on my FT-847, when running high-duty-cycle modes, it would drift up to 3-400Hz on 144MHz after 15-30mins of hard (WSJT, full power) use!

I found a mention of the QH40A Crystal Heater from DB6NT on, more information on: , which you place against the appropriate X-tal, to heat it to 40.8° C ±0.1° C

The total price, packaging and postage included (i.e. inside the EU), was € 14.

The heater unit is placed against the Reference X-tal, X1001, and connected to ground and +8-12V

Here the X-tal heater has been placed against X1001 and the wires attached

Jarl, OZ9MO has wrapped a piece of Copper foil around the Crystal before attaching the Crystal heater, in order to improve distribution of the heat to both sides of the crystal. Recommended!