On Wed, 14 Aug 2002 13:14:51 -0500 Jim writes: > "oven-compensated crystal oscillator" > > 1) Do you know what this could do to your power budget? > > 2) How about required warm-up times after power-up before > seeing those quoted accuracy specs? > > RF Jim I haven't done much RF work recently. Back when I was in broadcast, where we're allowed about 20 ppm (20 Hz for AM, 2 kHz for FM), the crystal was often mounted in a glass envelope with a vacuum. They seemed to have no trouble staying on frequency. An AM would drift a few Hz months to month. The 950 MHz studio to transmitter link we used had the transmit crystal for the PLL reference in an oven. This worked great until the thermostat got stuck. The main transmitter dropped off the air because the STL transmitter frequency went far enough from the receiver frequency that we lost the 110 kHz control subcarrier. I remember years ago seeing a PTC thermistor that clipped on a crystal can. It would self heat to hold the crystal at temperature. I think it was from murata. Of course, it'd be best to hold the oscillator and the crystal at a constant temperature. The original TXCOs were really a challenge since you had to use analog circuitry to match the tempco of the crystal and other circuitry. Now, I expect they use an eeprom to hold a table of trim values to bring it back on frequency for each temperature in the range. Harold FCC Rules Online at http://hallikainen.com/FccRules Lighting control for theatre and television at http://www.dovesystems.com Reach broadcasters, engineers, manufacturers, compliance labs, and attorneys. Advertise at http://www.hallikainen.com/FccRules/ . ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu