Economical is a very relative term. Something like this is ready to go:
http://www.ebay.com/itm/281701995263
I have no experience with this unit nor the seller but it looks good.
Another option is this:
http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7
I purchased one from this seller and have modified it to output 10MHz. It was only a handful of cheap parts to do so. The information is mentioned in his auction. If you need cheaper than $65, then the options get rather few.
The answer really depends on the precision you want. The following are in increasing order of cost / complexity / performance.
1. Zero-beat the OCXO against WWV at 10 MHz. Requires a 10 MHz shortwave receiver. Maybe 1 Hz accuracy.
2. Measure the carrier frequency of WWVB at 60 KHz. Requires a tuned LC circuit / antenna and amplifier for 60 KHz. Maybe 0.1 Hz.
Now you jump to accuracy levels in the 1e-9 to 1e-12 level.
3. Rb standard. Assumes that the unit is working and has been calibrated against a known standard. Drift is in the range of 5e-11 per month. Jitter isn't an issue.
4. Bare GPS receiver. Measure the output frequency. Usually 1 PPS although some units have an auxiliary output with a programmable frequency. Requires a decent antenna location. No drift. Jitter will be in the range of 5 - 100 ns rms depending on which unit you get. Make sure you get a timing GPS rather than a navigation GPS. Navigation GPS units can have 1 PPS jitter in the microsecond range.
5. GPSDO. Requires a decent antenna location. No drift. Jitter is < 1 ns rms.
This is a great list. I really want something that I don't have to periodically recalibrate. There's a window right where I would want to place a GPSDO, so I don't think antenna location will be an issue. So given that, a GPSDO seems like the way to go.
Any suggestions on options for that? What about the unit that Lightages posted a link to in the thread above? From the pictures in the listing, it looks like it is using a GPS chip intended for navigation (uBlox NEO-6M). Data sheet on that is here:
https://www.u-blox.com/images/downloads/Product_Docs/NEO-6_DataSheet_(GPS.G6-HW-09005).pdf
Economical is a very relative term. Something like this is ready to go:
http://www.ebay.com/itm/281701995263
I have no experience with this unit nor the seller but it looks good.
Another option is this:
http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7
I purchased one from this seller and have modified it to output 10MHz. It was only a handful of cheap parts to do so. The information is mentioned in his auction. If you need cheaper than $65, then the options get rather few.
The GPS option there looks good. I wonder if anyone here has any experience with that unit, though. I'm a bit leary about buying something from China with no confirmation that it's not junk.
2. Measure the carrier frequency of WWVB at 60 KHz. Requires a tuned LC circuit / antenna and amplifier for 60 KHz. Maybe 0.1 Hz.
The GPSDO that Edpalmer42 mentioned is down to $100 which is $25 less than when I bought one.
That's got to be the best deal around at the moment. It's NOS still in the original packing containers. Add a power supply, an antenna and you're good to go.
Economical is a very relative term. Something like this is ready to go:
http://www.ebay.com/itm/281701995263
I have no experience with this unit nor the seller but it looks good.
For $100, I think I'll give it a go. It seems like it will be a fun project to get that up and working. Any suggestions on PS and Antenna?
For $100, I think I'll give it a go. It seems like it will be a fun project to get that up and working. Any suggestions on PS and Antenna?
Any good quality power supply should be fine. People tend to prefer linear supplies for frequency references, but since most of the commercial units have internal switching supplies I don't think it makes much difference. It looks like each of the two units needs 24V at 2 amps. You don't have to run both units - remember that this was for Lucent who always specifies redundant systems - but it's probably best to start with both to make sure everything is working properly.
Any 5 volt GPS antenna will work. Some of the newer antennas are 3.3 volt only so look carefully. However, you'll get the best performance with a timing-grade antenna. They typically have narrower filtering than navigation antennas. Just search for <gps antenna timing> and start browsing.
The antenna should be mounted outdoors with a clear view of the sky towards the equator (since that's the direction where you'll see more satellites). You may be able to get away with an indoor antenna, but it will definitely reduce the signal levels and the number of satellites tracked. It may cause the unit to lose lock and go into holdover. More gain is better. These older GPSDOs tend to have poorer sensitivity than current ones. This could become an issue if you have a long cable run from the antenna to the receiver. In the manual for the Trimble Thunderbolt they recommend RG-59 or RG-6 cable between the antenna and the receiver. They basically say "Yes, we know it's 75 ohms and the equipment is 50 ohms. It doesn't matter. The cable is good, cheap, and widely available. Shut up and use it!" ... or words to that effect.
If you can set a long gate time on the counter and it measures low frequencies (1Hz) then you can check a 10MHz OCXO by using it as a reference and measuring the 1pps from a cheap (£30) GPS module.
I did this with my TF930 counter. Of course you need to do it over a long time as there is quite a lot of jitter from pulse-to-pulse.
The module I use is this one from Adafruit as it has an external antenna and is quite an accurate one ( 10nsecs according to the spec sheet - others are up to 50 nsecs or more):
http://proto-pic.co.uk/ultimate-gps-breakout-66-channel-w-10-hz-updates-mtk3339-chipset/
The other method is to use a scope, use the 1pps to trigger the scope and observe the phase shift on the 10MHz (assuming the phase shift is less than the 100 nsec period which it should be).
For $100, I think I'll give it a go. It seems like it will be a fun project to get that up and working. Any suggestions on PS and Antenna?
Any good quality power supply should be fine. People tend to prefer linear supplies for frequency references, but since most of the commercial units have internal switching supplies I don't think it makes much difference. It looks like each of the two units needs 24V at 2 amps. You don't have to run both units - remember that this was for Lucent who always specifies redundant systems - but it's probably best to start with both to make sure everything is working properly.
Any 5 volt GPS antenna will work. Some of the newer antennas are 3.3 volt only so look carefully. However, you'll get the best performance with a timing-grade antenna. They typically have narrower filtering than navigation antennas. Just search for <gps antenna timing> and start browsing.
The antenna should be mounted outdoors with a clear view of the sky towards the equator (since that's the direction where you'll see more satellites). You may be able to get away with an indoor antenna, but it will definitely reduce the signal levels and the number of satellites tracked. It may cause the unit to lose lock and go into holdover. More gain is better. These older GPSDOs tend to have poorer sensitivity than current ones. This could become an issue if you have a long cable run from the antenna to the receiver. In the manual for the Trimble Thunderbolt they recommend RG-59 or RG-6 cable between the antenna and the receiver. They basically say "Yes, we know it's 75 ohms and the equipment is 50 ohms. It doesn't matter. The cable is good, cheap, and widely available. Shut up and use it!" ... or words to that effect.
I decided to get the unit I posted earlier from ebay. It should make a nice video when I get back to making videos.
Heres my 2 cents worth.
After installing a High Stability Timebase Option (clone) for my 53131a I needed to calibrate it some how. I tried zero beating WWV's carrier but I quickly learned about the varying propagation delay caused by the variation of the ionosphere and receiving WWVH at the same time gave me too much error so my brother suggested using a GPS Disciplined Clock as a reverence source. The last time that I looked the cost was just way too much for me. Just recently I found the prices were getting reasonable so I purchased a Trimble Thunderbolt. After the 30 day warranty ran out it started to reboot on occasion so I found the BG7TBL GPSDO from China and decided what the hell, I will get one. I must admit, the build quality was pretty impressive and I liked the small size so I picked up 2 more as backups lol. With the el-cheapo supplied antenna placed on the north side of the house (north is bad) it tracks 12 birds most of the time. Just for giggles I stuck a resistor in the antenna connector and to my surprise it tracked 4 birds !
Screen shot of the BG7TBL: