http://elecraft.85.s1.nabble.com/Installed-K3EXREF-tp6188288p6208838.html
>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
>>
>______________________________________________________________
>Elecraft mailing list
>Home:
http://mailman.qth.net/mailman/listinfo/elecraft>Help:
http://mailman.qth.net/mmfaq.htm>Post: mailto:
[hidden email]
>
>This list hosted by:
http://www.qsl.net>Please help support this email list:
http://www.qsl.net/donate.html