> From:
[hidden email] <
[hidden email]>
> Subject: Re: [Elecraft] Installed K3EXREF
> To:
[hidden email]
> Date: Friday, March 25, 2011, 1:02 PM
>
> Glad you're going to give it a rest.....
>
> N5GE
>
> On Fri, 25 Mar 2011 09:45:31 -0700 (PDT), Wes Stewart
> <
[hidden email]>
> wrote:
>
> >I'm not picking on Paul, this is just a handy place to
> reply. I'm going to say this one more time (the first time
> was two years ago).
> >
> >I really don't understand all of the fuss about 1 Hz
> accuracy when just changing the K3 Width and Shift controls
> moves the frequency more than that and this is band
> dependent.
> >
> >On ten-meters I can listen to a crystal-controlled
> source and hear the beat note change as Shift and Width are
> adjusted.
> >
> >Elecraft considers its frequency conversion scheme to
> be proprietary but it's obvious that not all of the
> oscillators are moving at the same rate.
> >
> >Wes N7WS
> >
> >--- On Sat, 3/19/11, Paul Christensen <
[hidden email]>
> wrote:
> >
> >> 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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