Spectracom 8170 Modification
History of this 8170
The Spectracom 8170 is a WWVB 60Khz timecode receiver that can distribute accurate time using irig time codes. My first experience with this receiver was at my employment at the Naval Air Development Center in Warminster, PA. The center closed in 1996 but prior to that this receiver was used with a rooftop antenna to distribute accurate time to many areas of the complex including the computer department, various labs and the main entrance to the facility. The accurate time was distributed using existing internal phone lines. The signal was irig-B which was a code in the audio range of the phone lines. A master amplifier was used to distribute to the lines and simple irig-b readers were used to display the time at the remote locations.
It now being 30+ years since this was used one might ask why was this method of accurate time synchronization necessary. One must remember that this was before the Internet and before cell phones existed and the only way to accurately set clocks were time signals from the National Bureau of Standards, your local radio station, or calling on the phone. Yes, Bell Telephone had a number you oculd dial to get the time. But wait, you can still do that today! Just call 202-762-1401. Here is a nice article about this - Remember when you could call the time? Also this article describes Bell Telephones Frequency Standard
When the base closed in 1996 and I retired from Navy Civilian service a contractor took over quite a bit of the equipment. When the contractor eventually closed shop I got the word that some free equipment was available and being the scrounge I am I quickly showed up to acquire what I could and the 8170 receiver which I had installed and maintained 20 years before was part of the lot. At the time I was able to hook it to an outside antenna and sync to WWVB at my home. I later put it on the shelf and forgot about it. Twenty years later I am in a cleanup mode in my basement and decided to plug the 8170 in. It did not work and after some research I found out why.
WWVB changed their transmit format in 2013 which essentially made the 8170 non-functional. To improve their 60kHz range and reliability they added phase shift data transmission in addition to the AM level shift that had been in prior use. WWVB Enhanced Broadcast Format The phase shift completely confused the 8170 even though the amplitude shift was still there. I did some digging and cam across the "time-nuts" Internet forum and hooked up with Paul Swed, WB8TSL. He authored a mod for the 8170 which I tailored to my needs and it worked well. It uses a WWVB single chip receiver which has the amplitude level shift output to amplitude modulate a locally generated 60kHz signal. This works amazingly well even in eastern Pennsylvania. The gotcha for receiving these low frequencies is often local noise generated from many of the switching supplies, ECM motors, LED lighting, etc. that frequent today's homes. I had a considerable amount of noise being generated by my outside 12V landscape lighting which I converted over to all LED's. This brought about a quest to reduce the interference from them so I could reliably receive the low frequencies..
Click on any photo below for larger views
I started to investigate the noise problem from my landscape LED's and I found that a lot of the noise energy was going back into the power lines through the hefty 12V transformer I used to power the lights. So I investigated line filtering methods using hybrid common chokes. These chokes are available online such as these at Mouser But they are rather expensive and you really need to tailor them to the application. So knowing that all computers have rather high current switching supplies and they are class B rated it dawned on me that a friend who often works on computers might have a junk supply I could tear apart.
I installed one of the chokes and capacitors ahead of my 12V transformer and it really seemed to make a difference. The 60kHz receiver began to more reliably receive the 1PPS signal from WWVB. This is displayed on the LED so it can be visually seen. When noise or low signal are present the LED will flicker at a faster rate. So keep this in mind if you have low frequency noise from a source propagating back onto the power lines. You need to install a filter like this at the source of the problem.
So noise problem mostly solved now on to the the project
First you need to build the 60kHz signal source which will be modulated and feed to the the original receiver in the 8170. I decided to build this into a shielded box formed by cutting pieces of double sided PC board. I happened to have a lot of board. The copper box is not mandatory as you could use a small metal minibox or equivalent. It should be a box that can be shielded with incoming and outgoing signals bypassed or using coaxial fittings. I used BNC's.
The board was built using three TTL IC's a 7404, 74390, and 7400. Mostly wire wrap was used for connections. The schematic link below shows the wiring. Two sections of the 7404 along with a crystal are used as a 6Mhz oscillator. The 74390 is used as a divide by 100 yielding a 60KHz signal and a combination of gates in the 7404 and 7400 are used to modulated the signal. The modulated signal is 14db verses full signal for digital ones and zeros. The modulation rate is 1 PPS as per the WWVB broadcast format.
The output is tested to lock the 8170, lock LED on. I used a frequency counter and adjusted to 60kHz at the test output. Looking at scope patterns for the final output you should see a change in the signal level when you open or ground the modulation line. These are the actual signals that are sent to the 8170 receiver.
The following photos show the completed and labeled box.
Installation in the 8170
Since only need to drive the one WWVB receiver I opted to mount the box internally replacing the original rear panel BNC antenna connector with an RJ45 Ethernet connector. This facilitates the connection to the remote receiver.
Since the 8170 is to be used in a basement location the new WWVB receiver is remotely mounted and connected with standard CAT5 or 6 Ethernet cable. One pair is used for 12V power and another pair to transfer the TTL data. This was tested with 100 feet of CAT5 cable and worked well as the data rate is extremely low at 1 PPS.
The 8170 and receiver with 100 feet of CAT5 cable between them has been running now for over a month with no loss of sync during that period. The signal on the second floor of my home in Ricboro, PA about 20 miles north of Philadelphia has been steady 24/7. So ends a project that some would call meaningless given GPS and the Internet but being a radio enthusiast it is fun to directly receive and display terestrial time broadcasts sync'ed within milliseconds. Now that I am retired it is important to know what time it is. NOT!
This page last updated 4/5/2022
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