K3EXREF and Trimble Thunderbolts

[K2QI]

Brilliant - thanks to all for your replies.

I'll start looking for a used Thunderbolt to experiment with.  Sorry
if I missed this in an earlier exchange, but are there specific
Trimble model numbers known for recommended units?

Paul - I agree; can never hurt to have a disciplined reference source
for other projects.

Mni tnx es vy 73,
James K2QI

On Tue, Apr 5, 2011 at 3:40 PM, Paul Christensen <[hidden email]> wrote:

> Jim,
>
> In case you missed earlier comments, don't worry about phase noise
> performance of the external reference if you'll only use it with the K3.
> But, in addition to the K3, a high performance, low phase noise external
> reference can be distributed around the shack or work bench for other
> purposes.  I use a second output from the Trimble to phase-lock an ADAT
> transceiver.
>
> Paul, W9AC
>
> ----- Original Message -----
> From: "Paul Christensen" <[hidden email]>
> To: <[hidden email]>
> Sent: Tuesday, April 05, 2011 3:36 PM
> Subject: Re: [Elecraft] K3EXREF and Trimble Thunderbolts
>
>
>>> 1.  Any reference oscillator operating at 10 MHz would work with the
>>> K3XREF?
>>
>> The 10 MHz source should have a signal level between +4 dBm and +16 dBm.
>> For
>> square wave sources, 2VDC to 3.3VDC peak is optimum.  If the source is a
>> 5V
>> logic level, use a 50-ohm resistor in series with the input.
>>
>>> 2.  All that's needed for this to work is the K3XREF, updated
>> firmware, an accurate 10 MHz clock/oscillator, and a BNC cable?
>>
>> Yes.
>>
>>> 3.  Trimble Thunderbolt seems to be a good, cheap product to try.  Any
>> others that are > $100?
>>
>> Many.  For those not affraid of getting a soldering iron hot, I think the
>> Trimble units are pretty tough to beat.  Requires making a power cable to
>> a
>> triple-output power supply of your choice.  For a while, the HP Z3801A
>> units
>> were very popular.  These use noisy DC-DC internal converters, are power
>> hungry, but offer some of the best phase noise peformance of all the
>> GPS-DO
>> units.  The Trimble units have been documented to pretty much meet the
>> phase
>> noise performance of the Z3801A.   Rubidium is another choice in the USD
>> $100 range but these too will require some creative power connections.
>>
>>> What are the additional advantages of doing this other than knowing
>> you've pretty much eliminated any frequency drift?
>>
>> Really none I can think of, but as the weak-signal V/UHF ops have said,
>> that's reason enough!
>>
>> Paul, W9AC
>>
>>
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--
73 de James K2QI
President UNARC/4U1UN
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[Julian, G4ILO]

Thanks to Leigh for his detailed explanation. Also to you, Rich, for explaining how the frequency standard is applied to the K3.

I still have a couple of questions.

If, as I believe is the case, the K3 REF CAL has fairly large discrete steps, is there any benefit in using a reference oscillator that is many times more accurate than that? All one is looking for is something that will keep the K3 as accurate as it can be without the need to perform regular manual checks. A standard that has extra precision is not going to make the K3 any more accurate because the reference oscillator is being controlled using discrete steps.

Has anyone tested the effect of these small stepwise adjustments of frequency on the WSPR mode, in which the data is transmitted using a frequency shift of about 1.5Hz?

Julian, G4ILO

Rich Heineck wrote

The K3EXREF uses the 10 MHz standard as it's time base to measure the K3's TCXO and passes
an error value to the K3's MCU every few seconds.  No TCXO frequency control takes place,
thus no increase in phase noise.  Frequency compensation is done in software by
automatically updating the REF CAL function.  A relatively simple mechanism but effective :)

For my installation, I'm using a Thunderbolt, an $11 active antenna from Digi-Key, and a
30' run of RG-6, which works nicely with the F connector on the Tbolt.

[Don Wilhelm-4]

  Julian,

Please explain why you think any vfo tuning "steps" are related to a
frequency shift induced from the audio input to the K3.  I believe this
is mixing two entirely separate parameters.

I have not actually operated WSPR, but it cannot be that difficult (nor
that precise in practice).  I believe one would use DATA A sub-mode for
WSPR work.

The VFO places the waterfall within 1 Hz of the desired fequency with
the external reference (actually that could be within 50 Hz - same
argument).  Now the software applying the audio to the K3 has to shift
1.5 Hz (or 170 Hz for that matter),  As long as the K3 can tune the
desired frequency to be in the passband, the software and audio input to
the K3 will take care of the audio shift.  The only requirement is that
the K3 remain frequency stable once the frequency is selected - the rest
is done in the computer application software.

73,
Don W3FPR

On 4/5/2011 5:53 PM, Julian, G4ILO wrote:

> Thanks to Leigh for his detailed explanation. Also to you, Rich, for
> explaining how the frequency standard is applied to the K3.
>
> I still have a couple of questions.
>
> If, as I believe is the case, the K3 REF CAL has fairly large discrete
> steps, is there any benefit in using a reference oscillator that is many
> times more accurate than that? All one is looking for is something that will
> keep the K3 as accurate as it can be without the need to perform regular
> manual checks. A standard that has extra precision is not going to make the
> K3 any more accurate because the reference oscillator is being controlled
> using discrete steps.
>
> Has anyone tested the effect of these small stepwise adjustments of
> frequency on the WSPR mode, in which the data is transmitted using a
> frequency shift of about 1.5Hz?
>
> Julian, G4ILO
>
>
> Rich Heineck wrote:
>> The K3EXREF uses the 10 MHz standard as it's time base to measure the K3's
>> TCXO and passes
>> an error value to the K3's MCU every few seconds.  No TCXO frequency
>> control takes place,
>> thus no increase in phase noise.  Frequency compensation is done in
>> software by
>> automatically updating the REF CAL function.  A relatively simple
>> mechanism but effective :)
>>
>> For my installation, I'm using a Thunderbolt, an $11 active antenna from
>> Digi-Key, and a
>> 30' run of RG-6, which works nicely with the F connector on the Tbolt.
>>
>>
>
> -----
> Julian, G4ILO. K2 #392  K3 #222.
> * G4ILO's Shack - http://www.g4ilo.com
> * KComm - http://www.g4ilo.com/kcomm.html
> * KTune - http://www.g4ilo.com/ktune.html
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K3EXREF-and-Trimble-Thunderbolts-tp6242158p6243940.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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[Julian, G4ILO]

Don.

WSPR is AFSK with a very small shift at a very low rate. My thinking is that if a stepwise frequency correction was made during a transmit or receive period, it would cause a corresponding shift of the VFO which might be enough to throw the decoder of the receiver. I don't know, that's why I was asking.

K2ULR has told me off-list that he did not believe corrections are made while the K3 is transmitting. But it might still affect receiving. I think it is important to know because WSPR is one of those modes where frequency accuracy is really helpful and habitual users of the mode will probably be interested in the K3EXREF.

Don Wilhelm-4 wrote

Julian,

Please explain why you think any vfo tuning "steps" are related to a
frequency shift induced from the audio input to the K3.  I believe this
is mixing two entirely separate parameters.

I have not actually operated WSPR, but it cannot be that difficult (nor
that precise in practice).  I believe one would use DATA A sub-mode for
WSPR work.

The VFO places the waterfall within 1 Hz of the desired fequency with
the external reference (actually that could be within 50 Hz - same
argument).  Now the software applying the audio to the K3 has to shift
1.5 Hz (or 170 Hz for that matter),  As long as the K3 can tune the
desired frequency to be in the passband, the software and audio input to
the K3 will take care of the audio shift.  The only requirement is that
the K3 remain frequency stable once the frequency is selected - the rest
is done in the computer application software.

73,
Don W3FPR

[Dave-3]

Having done some long term measurements on my k3extref using an HP mHz
resolution counter i have seen no corrections during transmit. Once the k3
has "warmed up" (first thing in the morning it would take 10 minutes for the
original tcxo to stabilise enough for jt65/wspr/qrss(5Hz fsk)) I see very
few corrections being made on receive either.

All I need now is the release of the internal 144 xverter and I am good,
frequency stability wise thro 76GHz

Dave

ww2r

------------------------------

Message: 44
Date: Wed, 6 Apr 2011 00:58:58 -0700 (PDT)
From: "Julian, G4ILO" <[hidden email]>
Subject: Re: [Elecraft] K3EXREF and Trimble Thunderbolts
To: [hidden email]
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=us-ascii

Don.

WSPR is AFSK with a very small shift at a very low rate. My thinking is that
if a stepwise frequency correction was made during a transmit or receive
period, it would cause a corresponding shift of the VFO which might be
enough to throw the decoder of the receiver. I don't know, that's why I was
asking.

K2ULR has told me off-list that he did not believe corrections are made
while the K3 is transmitting. But it might still affect receiving. I think
it is important to know because WSPR is one of those modes where frequency
accuracy is really helpful and habitual users of the mode will probably be
interested in the K3EXREF.


Don Wilhelm-4 wrote:

>
> Julian,
>
> Please explain why you think any vfo tuning "steps" are related to a
> frequency shift induced from the audio input to the K3.  I believe this
> is mixing two entirely separate parameters.
>
> I have not actually operated WSPR, but it cannot be that difficult (nor
> that precise in practice).  I believe one would use DATA A sub-mode for
> WSPR work.
>
> The VFO places the waterfall within 1 Hz of the desired fequency with
> the external reference (actually that could be within 50 Hz - same
> argument).  Now the software applying the audio to the K3 has to shift
> 1.5 Hz (or 170 Hz for that matter),  As long as the K3 can tune the
> desired frequency to be in the passband, the software and audio input to
> the K3 will take care of the audio shift.  The only requirement is that
> the K3 remain frequency stable once the frequency is selected - the rest
> is done in the computer application software.
>
> 73,
> Don W3FPR
>
>

-----
Julian, G4ILO. K2 #392  K3 #222.
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

--
View this message in context:
http://elecraft.365791.n2.nabble.com/K3EXREF-and-Trimble-Thunderbolts-tp6242
158p6245052.html
Sent from the Elecraft mailing list archive at Nabble.com.


------------------------------

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[Edward R Cole]

Julian,

The REF CAL adjustment is in 1-Hz steps same as the fine tuning
resolution of the VFO.  The EXREF will call for a shift to bring the
radio frequency back to zero error by introducing a shift
command.  Typically, the TCXO does not drift much over a short time
(TCXO-3 is rated to 0.5 ppm).  The error depends on operating
frequency and is max at 50-MHz (0.5 ppm = 25 Hz).  But it is not like
the TCXO is jumping that far.  I watched it during the 30-min warm-up
of the K3 and it typically moves 1-Hz at a time until it settles out.

So I would not expect corrections over 1 or 2 Hz at maximum and they
are happening on a 4-second interval.  The TCXO is running
continuously and not being stepped.  The steps are commands to the
digital dividers in the synthesizer of the radio.  For example the
synth. steps when you rotate the VFO.

The advantage of the reference oscillator is that it makes the K3
more accurate in frequency.  Frequency stability and LO phase noise
are still controlled by the TCXO and not the reference.  To have the
radio stability and phase noise determined by the external source it
would require phase locking the TCXO to the reference signal.

I do not know enough about synthesizers or PLL so I am guessing there
is a momentary phase shift every time the K3EXREF commands a REF CAL change.

For robust FEC codes like WSPR it will not be a problem.  The sw
expects to have jumps and bumps to the data stream and removes them as noise.

The experts out there can correct my interpretation where it is in error.  I

73, Ed  - KL7UW

------------------------------

Message: 28
Date: Tue, 5 Apr 2011 14:53:00 -0700 (PDT)
From: "Julian, G4ILO" <[hidden email]>
Subject: Re: [Elecraft] K3EXREF and Trimble Thunderbolts
To: [hidden email]
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=us-ascii

Thanks to Leigh for his detailed explanation. Also to you, Rich, for
explaining how the frequency standard is applied to the K3.

I still have a couple of questions.

If, as I believe is the case, the K3 REF CAL has fairly large discrete
steps, is there any benefit in using a reference oscillator that is many
times more accurate than that? All one is looking for is something that will
keep the K3 as accurate as it can be without the need to perform regular
manual checks. A standard that has extra precision is not going to make the
K3 any more accurate because the reference oscillator is being controlled
using discrete steps.

Has anyone tested the effect of these small stepwise adjustments of
frequency on the WSPR mode, in which the data is transmitted using a
frequency shift of about 1.5Hz?

Julian, G4ILO




73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 144-1.4kw, 432-100w, 1296-testing*, 3400-winter?
DUBUS Magazine USA Rep [hidden email]
======================================
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[Leigh L. Klotz Jr WA5ZNU]

Edward R. Cole wrote

The REF CAL adjustment is in 1-Hz steps same as the fine tuning resolution of the VFO.

My experience with REF CAL shows that turning the knob 1 unit does not result in a 1Hz shift in the RX frequency.  

Leigh/WA5ZNU

[N5GE]

Leigh,

I'm confused (as usual).

Are you saying that with the K3EXREF I will not be able to make a 1Hz change in
RX/TX frequency with the VFOs?  That doesn't sound so good to me...

Please explain.

Thanks,

Tom
N5GE

On Wed, 6 Apr 2011 10:28:43 -0700 (PDT), "Leigh L. Klotz Jr WA5ZNU"
<[hidden email]> wrote:


>My experience with REF CAL shows that turning the knob 1 unit does not
>result in a 1Hz shift in the RX frequency.  
>
>Leigh/WA5ZNU

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[wayne burdick]

No -- Installing a K3EXREF has no impact on VFO use (at any tuning  
rate).

If you adjust REF CAL manually (i.e., with no K3EXREF unit installed),  
you can move the reference in 1-Hz steps, but as Leigh pointed out,  
the steps may not be exactly 1 Hz. This is due to DDS granularity.

Wayne
N6KR

On Apr 6, 2011, at 11:08 AM, [hidden email] wrote:

>
> Leigh,
>
> I'm confused (as usual).
>
> Are you saying that with the K3EXREF I will not be able to make a  
> 1Hz change in
> RX/TX frequency with the VFOs?  That doesn't sound so good to me...
>
> Please explain.
>
> Thanks,
>
> Tom
> N5GE
>
> On Wed, 6 Apr 2011 10:28:43 -0700 (PDT), "Leigh L. Klotz Jr WA5ZNU"
> <[hidden email]> wrote:
>
>
>> My experience with REF CAL shows that turning the knob 1 unit does  
>> not
>> result in a 1Hz shift in the RX frequency.
>>
>> Leigh/WA5ZNU
>
> ______________________________________________________________
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[James Maynard-2]

On 4/6/2011 5:47 AM, Dave wrote:
[in an e-mail with subject "Re: [Elecraft] (no subject)]

> Having done some long term measurements on my k3extref using an HP mHz
> resolution counter i have seen no corrections during transmit. Once the k3
> has "warmed up" (first thing in the morning it would take 10 minutes for the
> original tcxo to stabilise enough for jt65/wspr/qrss(5Hz fsk)) I see very
> few corrections being made on receive either.
>
> All I need now is the release of the internal 144 xverter and I am good,
> frequency stability wise thro 76GHz
>
> Dave
>
> ww2r
>

So, Dave, how did you manage to get a K3EXTREF?  I would like to install
one in my new K3, but as far as I can tell, it is not yet being offered
for sale.

I have long had an interest in the precise measurement of time and
frequency, and have several 10 MHz reference oscillators.  (The only
time that I participated in the ARRL FMT, I was limited by ionospheric
doppler, making a better measurement on the West Coast station than from
W1AW on the east coast.)

73, Jim K7KK
Saint Helens, Oregon, USA
"Remember, Ignorance is the Mother of Adventure!" -- Hagar the Horrible


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