This was an excellent explanation. I got a Trimble Thunderbolt off eBay for less than 200 bucks. It came from China and came with an antenna and power supply. If you are going to get one of the ones that come from China, make sure you get the power supply with it. The domestic Thunderbolts have a unipolar supply but the ones from China were specials and require a special bipolar power supply. As long as you're getting the power supply with it, you're OK. I have not noticed any noise from the power supply from China. I expect ferrites may solve the problem if found.
It works just fine with the stock Thunderbolt software. I've had mine for about 6 months and I've run tests using the Thunderbolt software. The PC monitoring software allows you to monitor the errors detected and log them. The accuracy is quite good. Although I see occasional errors greater than 1 part in 10^9, most of the measured errors are far less than 1 part in 10^9. I can't find any of the spreadsheets I generated (from many hours of operation) right now but I seem to recall that 1 sigma was down around 1 part in 10^10. This translates into a 1 Hz error at 10 GHz. The +/- 1 Hz error in the K3 is much greater than the accuracy of the GPSDO My primary reason for getting the GPSDO was for microwave and EME operations. Being able to use it with the K3 is a plus. I'm likely to be an early adopter of the production units when they become available. I will probably order my second K3 with a K3EXREF. Jerry - K0TV ----- Original Message ----- From: "Paul Christensen" <w...@arrl.net> To: <elecraft@mailman.qth.net> Sent: Saturday, March 19, 2011 9:34 PM Subject: Re: [Elecraft] Installed K3EXREF >I installed it on Friday in about 30 minutes, but I'm comfortable with my > way around the K3. I would think that most users could install it in > about > an hour or less. Installation is actually very simple with very few parts > involved. K3EXREF came with an SMA connector and SMA to BNC > between-series > adapter. > > Performance is exactly as promised by Elecraft. Although K3EXREF will not > phase lock the K3 to the external frequency source, I'm finding that it > stays within 1 Hz on 20m when locked to CHU at 14.670 MHz. I'm also > finding that testing for zero-beat to WWV at 10 MHz is not a good idea in > my > shack, and perhaps yours too. There are many 10 MHz signals being emitted > by nearby appliances, LAN routers, security system, Ethernet boards, etc. > That common, even frequency is everywhere in a household these days. > > In much of North America, CHU is an excellent source for testing since it > keeps cesium accuracy like WWV but the odd frequency of CHU is a real > benefit since the chance for beating against extraneous signals is much > smaller than at 10 MHz. Testing at a higher frequency rather than say the > MW broadcast band also provides for a reasonably good account of how the > K3EXREF performs. After installation, I would also suggest not trying to > test zero beat K3EXREF against commercial MW or SW BC stations since their > carriers are allowed to deviate much more than the cesium-based time and > frequency standards of CHU and WWV. Commercial AM broadcast station > frequencies are typically only accurate to about +/- 20 Hz although most > are > better than that. > > The K3's 49 MHz oscillator is only adjusted at intervals between 4 and 8 > seconds by K3EXREF in order to minimize jitter. The K3 retains its > original > phase noise performance since the external reference is not used internal > to > the K3's frequency generating scheme. Think of it this way -- K3EXREF is > like lightly touching the 49 MHz oscillator with a feather every few > seconds > if necessary to keep it within 1 Hz or so. Also, the K3 frequency stays > accurate even at the moment of powering up the K3. Kinda' fun to watch > the > 49 MHz oscillator display change during warm-up as it's being corrected > and > compared against the external reference. > > External references: There are three primary types, and all can be > purchased for less than USD $150 on the used market. Cesium standards (a > fourth type) are also available but are generally much more expensive, > complicated, and won't offer any benefit to K3 users since K3EXREF limits > resolution and accuracy to about 1 Hz. > > The first type is the GPS Disciplined Oscillator (GPS-DO). This type of > standard locks itself onto the visible GPS satellites orbiting the sky. > Requires a GPS antenna and is self-calibrating to the GPS satellites. The > GPS-DO's time and frequency averages from the visible satellites, each > satellite having it's own on-board cesium-based oscillator. Long-term > accuracy is usually good to at least 1 x 10^-11. Extreme accuracy and > only > a magnitude or two behind cesium. Look for Hewlett-Packard Z3801A, > Z3816A, > Trimble Thunderbolt, Brandywine, Symmetricon, and Datum models. Short > list, > but many others available. > > Rubidium is the next type. No GPS tracking needed. Accuracy commensurate > with GPS-DO. No antenna required. Long-term performance is highly > dependent on the quality of the optical beam from the rubidium pump lamp. > Look for EF Efratom, Datum, > > Third, is a high quality oven-controlled crystal oscillator (OCXO). > Requires periodic calibration. Accuracy good to at least +/- 0.05 ppm and > offer the best phase noise performance among the three types of > oscillators, > but as noted earlier, the excellent phase noise attributes of the OCXO > will > not be carried over to the K3. > > A shack reference oscillator is good for use with other equipment too > (e.g., > frequency counter). Although a bit lossy, I currectly use a > Mini-Circuits > passive three-way splitter, but one can purchase a distribution amp to > feed > many pieces of equipment from a single oscillator. Unlike the splitter, a > DA offers unity gain and very high port isolation. > > Finally, be mindful that most GPS-DO and rubidium units use internal > switch-mode DC-DC converters. Switching noise was bad enough on two of my > units that I decided to gut the converters and used an outboard > triple-output linear supply. The Trimble Thunderbolts that have been > retired from the cellular industry require an external triple-output > supply. > If choosing this model, get a linear type and avoid the headaches. > > Paul, W9AC > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
