> 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" <<a href="x-msg://39/user/SendEmail.jtp?type=node&node=6192128&i=1&by-user=t" target="_top" rel="nofollow" link="external">[hidden email]>
> To: <<a href="x-msg://39/user/SendEmail.jtp?type=node&node=6192128&i=2&by-user=t" target="_top" rel="nofollow" link="external">[hidden email]>
> 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
> >
> > ______________________________________________________________
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