Hi All, For stability it is enough to place the dongle in the middle of a big bucket filled with sand.
Look at figure 3 here: http://www.sm5bsz.com/linuxdsp/hware/mirisdr/thermal.htm With 10 litres of sand you can expect the frequency to stay well within 3 Hz at 144 MHz at room temperature. There is a sweet point where the temperature coefficient goes through zero. One can put a thermometer in the bucket and a heat source on top of it to find the sweet point and keep the temperature near for even better stability. The tests were done on the Mirics chip, but I guess the crystal oscillator is similar in all the dongles except for the FUN Cube Pro+ which has temperature control. Note that the supply voltage affects the frequency quite a lot. That is true even for the FUN Cube Pro+. It may be a good idea to supply the dongles with 5 V from an extra 5V supply that is very well regulated. Since the dongle is small we can temperature stabilize the whole thing, not just the crystal:-) That way we get both stability and reference accuracy. Note that changing the state of the dongle (current consumption) can cause a small frequency shift with this arrangement. Regards Leif / SM5BSZ > To achieve stability and reference accuracy, the time base crystal must be > removed and placed in a temperature controlled enclosure, or provided by a > commercially obtained TCXO. > > http://www.qsl.net/m0ayf/Crystal-Ovens.html > > http://www.crystek.com/documents/appnotes/Understanding_TCXOs.pdf > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Dan > Sent: Monday, March 31, 2014 9:58 PM > To: [email protected] > Subject: TCXO other than 28.8Mhz > > Hi, > > I need rtl-sdr TCXO with 1ppm. I need replace 28.8MHz at someone with 1ppm. > My sample rate is 2.048MHz. 28.8MHz with 1ppm is hard to find at digikey or > mouser. I would like to know is anyone has success replace TCXO other than > 28.8MHz > > Thanks > Dan > > Sent from my iPad > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2013.0.3465 / Virus Database: 3722/7286 - Release Date: 04/02/14 > >
