Thanks Willi,
That's is new to me. I have not disassembled the print stack jet. I expected some NTC an opamp and so on. The heater must be a PTC, these devices possesses a sharp rice of the resistance at a defined temperature, this way making a stable temperature. In the past I have used PTC's for that purpose. The lowest specific temperature available at that time was about 70 degrees C. I wonder what that temp of this device is. PTC's are widely used in the demagnetisation circuits in colour televisions, in series with de demagnetisation coil on the picture tube. As the resistance rises, the current can go down to almost nothing, provided that the PTC is thermally isolated. In the SDR1000 some current will flow due to the heat loss trough the oscillator. I do not think that the PTC is the culprit, the final temperature is only slightly dependent on the voltage, and will not give a fast nor step like change (in the frequency) as the heat transfer is also slowly. Still wondering what happens. 73 peter pa0pvn groeten Peter petervn(a)hetnet.nl <mailto:[EMAIL PROTECTED]> ; pa0pvn(a)hetnet.nl <mailto:[EMAIL PROTECTED]> ; pa0pvn(a)gmail.com ; pa0pvn(a)amsat.org . ________________________________ Van: Willi Reppel [mailto:[EMAIL PROTECTED] Verzonden: zo 7-1-2007 11:48 Aan: [EMAIL PROTECTED]; Brian Kassel; flexradio@flex-radio.biz Onderwerp: Re: [Flexradio] More Strange Frequency Drift Problem Peter, You wrote: >I am not sure where the power for the heater on the 200MHz oscillator come >from > I bought a new 1 W SDR1000 last month before the announcement about the 100 W-only version came. I disassembled the unit to have a look at the termistor. It is a small disk of approx 8 mm diameter and 2 mm thickness which is soldered or glued with a conductive compound on to the case of oscillator QG1. A wire is soldered to the top of the disk which is connected directly to the terminal strip and + 13.8 V dc. The grounded case of the crystal oscillator serves as return pass and minus. It seems to be a combined heater / termistor with approx 50 ohm att room temp. and 150 ohm at operation temp. Hope this sheds some light upon how the preheater / termistor is fed. groeten van SM6OMH Willi ---- snip ---- -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.flex-radio.biz/pipermail/flexradio_flex-radio.biz/attachments/20070107/27a3dd46/attachment.html _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com/ FlexRadio Knowledge Base: http://kb.flex-radio.com/
