Using a 32khz TCXO as a 28.8mhz oscillator reference? - Page 1
Forum section: electronics / projects

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: June 24, 2016, 12:23:52 am
content: Basically I paid about 20 dollars for a 28.8mhz TCXO and this morning I accidently hooked it up in reverse polarity and now it doesnt work. I have painstakenly built a 5 pole LP filter for the TCXO. I need a good 28.8mhz source that is stable I had an SI5351 board and AS9850 in a bag I have been searching for for 3 hours with no luck.I cant get another oscillator for at least a week plus shipping time... Im looking for a way to get a stable frequency source, I have 28.8mhz xtals but this is an LO for RF and I want to built the best frequemcy source I can. I have a ton of TCXO's some under 28.8 and some WAY over, but I have these nice little maxim TCXO's for real time clocks and I was wondering if I could use that.Anyways If anyone can point me to a web page or something showing how to build an oscillator from a different frequency reference that would be awesome!

author: uncle_bob
author_rank: Unknown
timestamp: June 24, 2016, 12:40:33 am
content: Quote from: rwgast_lowlevellogicdesin on June 24, 2016, 12:23:52 amHiA TCXO is far from "the best" frequency source you can get. It's also far from the worst. The first thing you need to do is to figure out what sort of specifications you actually *need*. Stability is one, there are a *lot* of other specs. Once you have that worked out ... then start picking out an oscillator.Mouser or Digikey will each get you a replacement oscillator for not a lot of money and in less than a week. It all depends on what you need.Bob

author: Kleinstein
author_rank: Super Contributor
timestamp: June 24, 2016, 06:12:00 am
content: A 32 kHz crystal is not really good when it comes to phase noise - so the normal 28 MHz crystal is likely way better than the 32 kHz followed by a PLL, unless the PLL is using something like the 28 MHz crystal to build a VCXO and the 32 kHz only for very slow corrections similar to GPSDOs.P.S. 28.8 mHz is a really low frequency for radio.

author: uncle_bob
author_rank: Unknown
timestamp: June 24, 2016, 01:22:18 pm
content: HiA few things about a source in terms of it's use in a radio:1) What does it's phase noise plot look like?2) Do you need to multiply it for the frequency to be useful?3) Now what does the phase noise plot look like?4) Does the output signal make sense or do you have to convert it to something else?5) Does it have low enough spurious to be useful?6) Can it be tuned on frequency / is this even needed ?7) How much work is it to get it to a useful frequency?Does it pull to much power?9) Does it warm up fast enough?10) Are things like shock / vibration / acceleration an issue?11) What sort of aging performance is needed?12) What is the temperature range?13) What is the likely temperature change?14) What is the required temperature stability / radio stability?Lots of things to look at before you start putting things together. There are a *lot* of sites that will show you how to turn a bare crystal into an oscillator. First you need to work out what makes sense.Bob