[ntp:questions] Inexpensive home reference clock - WWVB/CDMA?

Jason Rabel jason at extremeoverclocking.com
Sun Jul 1 21:41:42 UTC 2007

What GPS antenna did you use? Was it passive or +5V? What was the rated dB
gain? Did you try sticking the antenna a few inches out past your window?
Sometimes you can increase your signal dramatically just by doing that. Also
depending on where you live if you only have a partial view you want it to
face towards the equator for the most satellites.

Maybe you could make friends with the person on the top floor and they would
let you mount an antenna on a PVC pipe outside their balcony which would get
you a clear view of the sky then you can just run the cable down the outside
wall into your apt.

WWVB receivers will sometimes pop up on eBay, usually the older TrueTime
models. With those the serial output can be set to once a second which NTP
can then read in. For the best accuracy you should use the PPS signal too,
however that is only supported in FreeBSD, Solaris, and Linux (with kernel

IIRC, NTP will support WWV (not WWVB) via an audio input to your sound card.
This is a DIY project, I've seen a couple on the net and it doesn't seem to
require too much assembly, just finding the right parts (antenna) could be
the challenge.

I'm unsure about the RadioSync and NTP, best thing would be to contact them
about it or read more on their site, I'm sure they get that question all the
time. $199 for a modern timing receiver like that seems quite reasonable.

Another hurdle might be interference with the WWVB signal, but without
having any equipment to test beforehand you are kind of diving in blind. A
CDMA receiver you can test beforehand just seeing how good of a signal you
get with your cell phone.


> As a time geek, I've been looking at getting either a WWVB or CDMA 
> reference source to provide timing to my network here at home, and to 
> the NTP pool.
> Due to my location (apartment complex, first floor) I have no roof 
> access and poor GPS signal through the window, so GPS timing is out.
> I've considered making a WWVB receiver, but I'm a time geek, not an 
> electronics geek, and would spend more on necessary things (soldering 
> iron, for example) than it'd cost for me to buy a commercial product.
> There are two possible commercial products I'm looking at: Beagle 
> Software's ClockWatch Radio Sync (WWVB receiver, $199.95) and Cell Sync 
> (CDMA, $649.95). Alas, neither of them are available on eBay for cheap.
> Does anyone have any experience with either? I presume that when 
> connected to an RS-232 serial port that NTPv4 should have no trouble 
> getting time from either.
> I'm looking at the Radio Sync clock, simply because I'm a Cheap 
> Bastard(tm) and don't have much money to spend. This would be more than 
> adequate for my purposes, and I believe it would be adequate for 
> providing time to the NTP pool. Is there any reason why I should not 
> deploy a WWVB clock to the NTP pool or advertise it as a stratum 1 
> server for public use? While it might not provide as precise a time 
> signal as CDMA or GPS references, it should be well within the margin of 
> error for internet based timekeeping, right?
> That said, does anyone happen to have any surplus WWVB or CDMA clocks 
> lying around that they'd consider selling to a fellow time geek?

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