It's certainly better than no reference at all but to be fair 1ppm is only really useful for a straightforward crystal oscillator, or perhaps a TCXO. Good ovened oscillators are stable enough to try to set them up to 1x10-8 to 1x10-9, Rubidium units should be in the in the 10-9 to 10-11 range.
I agree that 1ppm is pretty useless.
You can get a lot better than 1ppm by a DIY TXCO design (but it's messy of course).
I don't really consider anything a decent reference standard unless it's at least rubidium. e.g. > x10-9
Sure you can get some good oven based oscillators, but they just aren't really the same level.
Thanks for the thoughts guys. To be fair, Kasper does say the Network Tranfer Frequency (NTF) project is
better than 1ppm.
And after all Dave, you're on record as saying, "
But hey, yeah, point six ppm - Good enough for Australia."
OK, I admit, I'm taking your comment slightly out of context - but equally, a lot of hobbyists probably rely on a calibration lab to make the best of an "awful stock oscillator" in equipment like an Agilent 53131A. If they could achieve the same level of accuracy as you achieved with that Agilent Universal Counter using the NTF, like you say, "good enough".
1ppm is a few orders of magnitude less than ideal for a true standard, I agree, but for those of us just starting out, or on limited budget, or only building 'hobby' projects, I'd argue it's all about making do. So it would be
really interesting to see how much better than 1ppm the NTF is - if anyone with a rubidium standard could spare the time please
If anyone's willing, here's the NFT project file links again:
n1.taur.dk/nft/nft.pdf
n1.taur.dk/nft/nft.exe
And if you could elaborate on
how many order's of magnitude better a frequency standard
really must be to satisfactorily calibrate a given counter for a desired level of accuracy, that would be useful info too.
Just to put things in perspective, ±1ppm is ±0.0864 sec/day for a standard (typically 10 - 20 ppm) 32.768 kHz quartz crystal found in nearly all electronic wrist watches. That's ±2.6 sec/month - and although most electronic watch manufacturers don't advertise products with a spec that good, many achieve it. So everything's relative to its intended use. Speaking of which, the reason I'm really interested in all this 'making-do' is for calibrating the 32.768 kHz quartz oscillator in the
Open source Time Machine Project #2 (OTM-02) - a watch module for hobbyists and makers using the latest 128 x 128
Memory LCD and
EFM32 ARM Cortex-M3.
Here's where the project's at as of a few days ago:
I'll make a new thread in the EEVBlog Open Source Projects forum when I get a moment - and after getting the first code running later this week, all going well.
Cheers guys - look forward to maybe seeing some results comparing Rubidium and NFT.