A recent news story about the 50th anniversary of WWVB got me to thinking about building my own WWVB receiver. I Googled “wwvb kits” and came up with the following:
- WWVB NIST Radio Time Receiver Kit
- WWVB Chiming Clock Kit
- WWVB 60 kHz Time Receiver Module with Antenna
Unfortunately, all of these kits use a little PC board made by a company called C-MAX, and the company has either discontinued making the IC that powers this module or simply quit selling this module in the U.S. As recently as a couple of years ago, Digikey actually sold this module for about seven bucks.
There are several Web pages that show how to interface the CMMR-6 module to an Arduino or a PIC processor. Here are two:
A couple of companies in the UK seem to still have the modules in stock. The price from a company called Earthshine is only six pounds, but that doesn’t include shipping, of course.
There are some plans that don’t use the C-MAX chip, but, of course, they’re much more complex. One guy designed his own receiver, but it’s quite a bit more complex than simply using a single chip. There are also several commercial receivers available, but the cheapest one I found is $220.
There are several Web pages that describe how to use the WWVB receiver modules from “atomic clocks.” One of the projects scavenges the WWVB module from a Sony clock. The second uses the module from an Atomix 13131. The Atomix 13131 costs as little as $13.
So, I’m still unsure which way I’m going to go here, but it looks as though hacking an existing clock might be the way to go, especially if I can find one at a thrift shop or garage sale.
Beware the ‘bargain’ atomic clocks. I picked one up at Dayton a couple of years ago for $10, and found out why the guy in the flea market had a whole pile of them for that price — the receiver code is buggy, in that if there are any bit errors, it ends up putting improbable time/date on the display. I have this particular clock on top of my overhead at work in the middle of a giant cube farm. It usually gets enough signal at night to sync up OK, but occasionally I come in to be greeted with some oddball time and/or date. I then carry it over to the nearest window and force a manual sync. After a few minutes, it rights itself.
Another reason that a lot of atomic clocks may show up surplus cheap, is that WWVB added phase shift keying to their output, so a newew crop of receivers will start to show up that can take advantage of the more robust modulation scheme.
I’d be OK with buggy software. I want to scavenge the RF portion of it anyway and do my own thing with it.
This is a neat idea. You might even be able to do it using a direct-sampling microcontroller (e.g., Arduino) as a DSP since the frequency and data rates are not onerous. NIST has documented the time code format. The RF side of things really just needs to have enough gain to use a crummy antenna and decent rejection to AC and switching power supply junk. There are some simple receiver circuits out there for interfacing VLF E-field probe antennas to a sound card. Of course, the frequency roll-off would be different, but it might give some hints as to the required components.
Alternative: Obtain a cheap GPS receiver and use the NMEA serial output to get GPS time. GPS modules are available, of course, but old hiking-type receivers without mapping features can sometimes be picked up cheaply on the used market, and usually have serial outputs for NMEA data. I think NMEA sentences only report time data to a resolution of one second, though, so if you need millisecond accuracy this probably won’t work.
The NEMA sentences only have second resolution, but most of those modules have an accurate PPS output. You use that as an interrupt source to clear out the fractional portion of the second and use the NEMA sentences to set everything else.
That is not quite true. NEMA does not specify time resolution — it is up to the chip. I have used many GPS chips over the years and those that provide updates at 5 or 10 times a second also provide the 200 and 100 ms resolution accurately.
How about this one:
http://www.pvelectronics.co.uk/index.php?main_page=product_info&products_id=82
I bought two of these from PV Electronics in the UK, one of the standard models and one of the sensitive models. Total shipping was only $5 and both arrived in a week or so in good shape. I thought I would report my experience.
The electronics appear to be the same for both units, a small circuit board about 1 x 2 cm, only the antenna ferrite rod is a little longer for the “sensitive” model. All workmanship appears to be satisfactory. The antenna is a ferrite rod with many turns of fine wire and a capacitor in parallel that makes it resonant at about 60 kHz (the carrier frequency of WWVB). The antenna is fragile and the flying leads are very easy to break off (yes, I learned the hard way).
I tried to connect one to my Ice Clock (http://learn.adafruit.com/ice-tube-clock-kit) which uses an Atmel microprocessor (same family as arduino). I checked the schematic of the clock and found places to grab 5V Vdd, ground and an unused Atmel input pin for reading the time code. I modified the firmware to read the WWVB time clicks and set the time when two consecutive minutes were consistent.
However the results were not satisfactory for the following reasons:
1. Even the “sensitive” model does not copy the WWVB signal reliably here in Tucson. My Casio Wave Ceptor WWVB watch works fine, even on the same bench on which I was working with the PV at the same time.
2. The PV unit does not always start or stay running. It contains a 60 kHz crystal and sometimes I had to tap it to get it to start oscillating and sometimes it would just stop and need another tap.
3. The oscillator also stops when the room lights are on. Something in their circuit is sensitive to light. Covering the PV with black tape helped.
4. Although advertised to work with both 3.3 and 5V systems, my PVs would not receive powered with 5V. I only had 5V on my Ice Clock so I measured the current draw and put a 47 ohm resistor in series with the PV Vdd so it was getting about 3.3V.
Both circuit boards behaved the same in all these respects, which suggests these are design issues, not random variation. I did finally get them to function and I enjoyed the exercise, but I do not consider these units to be a reliable source of time.
73, Elwood, WB0OEW
Thanks for the report, Elwood. Maybe the unreliability is one reason these aren’t being made anymore. It’s looking more and more as if I should find a WWVB clock at the local thrift shop or recycle center and hack it.
I found out that the new phase encoded technique rolled out recently for WWVB was actually developed under contract by a company in Dallas called XTendWave (see http://www.xtendwave.com). They’ve developed a matching decoder chip called EverSet that is expected to be released later this year. I contacted them and they’ve graciously agreed to send me some samples when they come out. Should be fun to have a go with these.
Hmm…it’s now 8 months later, and they still are only saying “Xtendwave is currently making prototypes available to select customers.”
So, wondering if/when they have a commercially available product….?
I have several of the WWVB modules from PV Electronics and they all work great. Note that the PON input must be grounded. If it’s left floating, you can experience intermittant shutdown of the receiver. Also, the modules do NOT work well from most switching power supplies, such as USB 5V wall warts. I receive WWVB pretty well here in Michigan, but only at night. Hope this helps. -73’s
So what is the propagation mode for the transmission.
It must be ground wave, no?
Just want to add that receiver kits are available from Universal-Solder.ca, to find in the onlineshop, on eBay and Amazon. These kits are featuring a receiver chip from Finland (MAS) and are better than the old C-MAX chip.
Another news: The ES100 called phase modulation receiver kits with 2 antennas are also in the pipeline, and will be offered exclusively from Universal-Solder.ca by October or November 2018.
Volker