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K3/K3S receiver and high-precision frequency determination?

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Frank O'Donnell

K3/K3S receiver and high-precision frequency determination?

Sometime (probably last year) I remember seeing a discussion of why the
K3/K3S receiver isn't suitable to do high-precision frequency
measurement tests at the level of hundredths of a Hertz. As I vaguely
recall, the receiver is designed so that its frequency actually varies a
bit intentionally, and I remember someone posting a plot demonstrating
this. However, I'm striking out on finding any of those posts. Can
anyone either help with them, or point to any other
discussion/explanation on this?

Thanks much,

Frank K6FOD

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Wes Stewart-2

Re: K3/K3S receiver and high-precision frequencydetermination?

I don't recall that discussion you're talking about, but I can say the K3(s) has
nowhere near that stability or resolution. (At least mine doesn't) I don't know
why Elecraft would design intentional instability into the radio.

During a recent thread about the TCXO option, I did some quick-n-dirty
measurements of my old K3 with standard reference and my newer K3S with the high
stability reference. I have a cable that I can run from the reference board to
a frequency counter (BG7TBL FA-2 w/Bodnar GPSDO reference). For this I have to
remove the top covers on the radios. I found the old radio to be inaccurate but
precise. I could touch the crystal oscillator and see the frequency move from
temperature effects but recover quickly. The TCXO was another story. It moved
around when I just laid a sheet of paper over the open box. I didn't quantify
this as I had to move on to other things; maybe later.

The frequency conversion scheme in these radios is proprietary but it entails a
lot of fussing around, with sideband switching, bandwidth adjusting, etc. All
of this AFAIK is done with DDSes which are not exact, they move in steps, albeit
little steps, but steps nonetheless.

If you want better you might look at the past results of the ARRL FMT (which
coincidentally was held last night) to read the soapbox comments of what other
folks are using.

http://fmt.arrl.org/fmtresults.php

Wes N7WS

On 4/24/2020 10:11 AM, Frank O'Donnell wrote:

> Sometime (probably last year) I remember seeing a discussion of why the K3/K3S
> receiver isn't suitable to do high-precision frequency measurement tests at
> the level of hundredths of a Hertz. As I vaguely recall, the receiver is
> designed so that its frequency actually varies a bit intentionally, and I
> remember someone posting a plot demonstrating this. However, I'm striking out
> on finding any of those posts. Can anyone either help with them, or point to
> any other discussion/explanation on this?
>
> Thanks much,
>
> Frank K6FOD

NK7Z

Re: K3/K3S receiver and high-precision frequency determination?

In reply to this post by Frank O'Donnell

Hi,

That was me... I used to use my Icom 756 Pro, to watch the Doppler on
changes in the ionosphere, and on Meteors. The K3 uses steps to correct
frequency, while the Icom did not. Analog vs. Digital corrections.

Accuracy is not an issue, it is the steps... They destroy the
continuity of the tracking... I should have some captures if you are
interested. Email me off list and I'll send a set.

The issue for me, I am looking for changes in frequency, on the order of
sub-1 hz., not looking to get an exact reading on the frequency, just
changes in frequency across minutes, not days or hours.

I don't need to be dead on for frequency, but I do need to have a
straight line that is affected by Doppler, and path changes. I can't
get that with my K3 without those annoying steps.

Keep in mind we are talking worst case 6 or 10 Hz., and the steps appear
to be far, far, smaller than that...

So... I have given this aspect of the hobby up. I did just get the
TXCO installed along with a lot of extras on my K3, and the steps are
longer, but still there... I will get some older rig that is analog in
nature and return to that aspect of the hobby then...

I was able to watch echos from aircraft between Eugene, and Portland
Oregon, (about 100 miles apart), using the KGW TV, (Ch. 2), aural
carrier as a source. I got the coolest traces of Doppler shifts caused
by the aircraft movement. Meteors were far more interesting... Anyway,
it is not an issue of Frequency accuracy, bit one of how the rig makes
adjustments. I would love to just turn off the steps, and accept the
drift over longer times. Oh well... Hope that helps... It is NOT the
K3 having an issue with measuring frequency...

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 4/24/20 10:11 AM, Frank O'Donnell wrote:

> Sometime (probably last year) I remember seeing a discussion of why the
> K3/K3S receiver isn't suitable to do high-precision frequency
> measurement tests at the level of hundredths of a Hertz. As I vaguely
> recall, the receiver is designed so that its frequency actually varies a
> bit intentionally, and I remember someone posting a plot demonstrating
> this. However, I'm striking out on finding any of those posts. Can
> anyone either help with them, or point to any other
> discussion/explanation on this?
>
> Thanks much,
>
> Frank K6FOD
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]

Frank O'Donnell

Re: K3/K3S receiver and high-precision frequency determination?

Dave,

Thanks, that may have been the thread I was remembering.

While searching old messages, I also came across a post from Ed Cole
KL7UW from June 2018 in which he stated that, even if an external
reference is connected, the K3 frequency "is established by the
[internal] TCXO and the external reference merely performs a periodic
check. ... the EXREF system does not phase-lock the TCXO. It
periodically corrects the error but the TCXO drifts normally between
freg corrections ... . Now if you want to know why Elecraft chose
periodic freq correction over true phase-locking, the answer is low LO
phase noise. Much harder to get low phase noise in a PLL than in a TCXO."

73,

Frank K6FOD

On 4/24/20 12:37 PM, Dave Cole wrote:

> Hi,
>
> That was me... I used to use my Icom 756 Pro, to watch the Doppler on
> changes in the ionosphere, and on Meteors. The K3 uses steps to
> correct frequency, while the Icom did not. Analog vs. Digital
> corrections.
>
> Accuracy is not an issue, it is the steps... They destroy the
> continuity of the tracking... I should have some captures if you are
> interested. Email me off list and I'll send a set.
>
> The issue for me, I am looking for changes in frequency, on the order
> of sub-1 hz., not looking to get an exact reading on the frequency,
> just changes in frequency across minutes, not days or hours.
>
> I don't need to be dead on for frequency, but I do need to have a
> straight line that is affected by Doppler, and path changes. I can't
> get that with my K3 without those annoying steps.
>
> Keep in mind we are talking worst case 6 or 10 Hz., and the steps
> appear to be far, far, smaller than that...
>
> So... I have given this aspect of the hobby up. I did just get the
> TXCO installed along with a lot of extras on my K3, and the steps are
> longer, but still there... I will get some older rig that is analog
> in nature and return to that aspect of the hobby then...
>
> I was able to watch echos from aircraft between Eugene, and Portland
> Oregon, (about 100 miles apart), using the KGW TV, (Ch. 2), aural
> carrier as a source. I got the coolest traces of Doppler shifts
> caused by the aircraft movement. Meteors were far more
> interesting... Anyway, it is not an issue of Frequency accuracy, bit
> one of how the rig makes adjustments. I would love to just turn off
> the steps, and accept the drift over longer times. Oh well... Hope
> that helps... It is NOT the K3 having an issue with measuring
> frequency...
>
> 73, and thanks,
> Dave (NK7Z)
>
> On 4/24/20 10:11 AM, Frank O'Donnell wrote:
>> Sometime (probably last year) I remember seeing a discussion of why
>> the K3/K3S receiver isn't suitable to do high-precision frequency
>> measurement tests at the level of hundredths of a Hertz. As I vaguely
>> recall, the receiver is designed so that its frequency actually
>> varies a bit intentionally, and I remember someone posting a plot
>> demonstrating this. However, I'm striking out on finding any of those
>> posts. Can anyone either help with them, or point to any other
>> discussion/explanation on this?
>>
>> Thanks much,
>>
>> Frank K6FOD

NK7Z

Re: K3/K3S receiver and high-precision frequency determination?

Thanks for the explanation, I have always wondered why... I'm good with
low phase noise, Low phase noise means less splatter from radios!

All the folks close to me have purchased K3s, so even though they are
close, it is not too bad. I had a friend that lived 700 feet from me,
and had a Collins S-Line, including the KW... It was horrid for being
far too wide... He switched to a K3, and for the most part things were
far better. Prior to the switch, I could not operate on the same band
when he operated, after he switched to the K3, I could!

I took P3 screen shots of the change from old to new synthesizer, as I
changed to the new one, and as he changed to the new one. It is totally
obvious how much better the new synthesizer is than the old... See:

https://www.nk7z.net/k3/

for the screen shots.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 4/24/20 1:03 PM, Frank O'Donnell wrote:

> Dave,
>
> Thanks, that may have been the thread I was remembering.
>
> While searching old messages, I also came across a post from Ed Cole
> KL7UW from June 2018 in which he stated that, even if an external
> reference is connected, the K3 frequency "is established by the
> [internal] TCXO and the external reference merely performs a periodic
> check. ... the EXREF system does not phase-lock the TCXO. It
> periodically corrects the error but the TCXO drifts normally between
> freg corrections ... . Now if you want to know why Elecraft chose
> periodic freq correction over true phase-locking, the answer is low LO
> phase noise. Much harder to get low phase noise in a PLL than in a TCXO."
>
> 73,
>
> Frank K6FOD
>
>
> On 4/24/20 12:37 PM, Dave Cole wrote:
>> Hi,
>>
>> That was me... I used to use my Icom 756 Pro, to watch the Doppler on
>> changes in the ionosphere, and on Meteors. The K3 uses steps to
>> correct frequency, while the Icom did not. Analog vs. Digital
>> corrections.
>>
>> Accuracy is not an issue, it is the steps... They destroy the
>> continuity of the tracking... I should have some captures if you are
>> interested. Email me off list and I'll send a set.
>>
>> The issue for me, I am looking for changes in frequency, on the order
>> of sub-1 hz., not looking to get an exact reading on the frequency,
>> just changes in frequency across minutes, not days or hours.
>>
>> I don't need to be dead on for frequency, but I do need to have a
>> straight line that is affected by Doppler, and path changes. I can't
>> get that with my K3 without those annoying steps.
>>
>> Keep in mind we are talking worst case 6 or 10 Hz., and the steps
>> appear to be far, far, smaller than that...
>>
>> So... I have given this aspect of the hobby up. I did just get the
>> TXCO installed along with a lot of extras on my K3, and the steps are
>> longer, but still there... I will get some older rig that is analog
>> in nature and return to that aspect of the hobby then...
>>
>> I was able to watch echos from aircraft between Eugene, and Portland
>> Oregon, (about 100 miles apart), using the KGW TV, (Ch. 2), aural
>> carrier as a source. I got the coolest traces of Doppler shifts
>> caused by the aircraft movement. Meteors were far more
>> interesting... Anyway, it is not an issue of Frequency accuracy, bit
>> one of how the rig makes adjustments. I would love to just turn off
>> the steps, and accept the drift over longer times. Oh well... Hope
>> that helps... It is NOT the K3 having an issue with measuring
>> frequency...
>>
>> 73, and thanks,
>> Dave (NK7Z)
>>
>> On 4/24/20 10:11 AM, Frank O'Donnell wrote:
>>> Sometime (probably last year) I remember seeing a discussion of why
>>> the K3/K3S receiver isn't suitable to do high-precision frequency
>>> measurement tests at the level of hundredths of a Hertz. As I vaguely
>>> recall, the receiver is designed so that its frequency actually
>>> varies a bit intentionally, and I remember someone posting a plot
>>> demonstrating this. However, I'm striking out on finding any of those
>>> posts. Can anyone either help with them, or point to any other
>>> discussion/explanation on this?
>>>
>>> Thanks much,
>>>
>>> Frank K6FOD
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]

donovanf

Re: K3/K3S receiver and high-precision frequency determination?

Each of these frequency jumps causes phase discontinuity that is likely
to cause bit errors in during PSK modulation and demodulation.

How often do they occur?

73
Frank
W3LPL

----- Original Message -----

From: "Dave Cole" <[hidden email]>
To: [hidden email]
Sent: Friday, April 24, 2020 9:09:52 PM
Subject: Re: [Elecraft] K3/K3S receiver and high-precision frequency determination?

Thanks for the explanation, I have always wondered why... I'm good with
low phase noise, Low phase noise means less splatter from radios!

All the folks close to me have purchased K3s, so even though they are
close, it is not too bad. I had a friend that lived 700 feet from me,
and had a Collins S-Line, including the KW... It was horrid for being
far too wide... He switched to a K3, and for the most part things were
far better. Prior to the switch, I could not operate on the same band
when he operated, after he switched to the K3, I could!

I took P3 screen shots of the change from old to new synthesizer, as I
changed to the new one, and as he changed to the new one. It is totally
obvious how much better the new synthesizer is than the old... See:

https://www.nk7z.net/k3/

for the screen shots.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 4/24/20 1:03 PM, Frank O'Donnell wrote:

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Post: mailto:[hidden email]

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Post: mailto:[hidden email]

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NK7Z

Re: K3/K3S receiver and high-precision frequency determination?

With the TXO on the order of one every few minutes, without on the order
two a minute or so.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 4/24/20 2:15 PM, [hidden email] wrote:

> Each of these frequency jumps causes phase discontinuity that is likely
> to cause bit errors in during PSK modulation and demodulation.
>
> How often do they occur?
>
> 73
> Frank
> W3LPL
>
> ------------------------------------------------------------------------
> *From: *"Dave Cole" <[hidden email]>
> *To: *[hidden email]
> *Sent: *Friday, April 24, 2020 9:09:52 PM
> *Subject: *Re: [Elecraft] K3/K3S receiver and high-precision frequency
> determination?
>
> Thanks for the explanation, I have always wondered why... I'm good with
> low phase noise, Low phase noise means less splatter from radios!
>
> All the folks close to me have purchased K3s, so even though they are
> close, it is not too bad. I had a friend that lived 700 feet from me,
> and had a Collins S-Line, including the KW... It was horrid for being
> far too wide... He switched to a K3, and for the most part things were
> far better. Prior to the switch, I could not operate on the same band
> when he operated, after he switched to the K3, I could!
>
> I took P3 screen shots of the change from old to new synthesizer, as I
> changed to the new one, and as he changed to the new one. It is totally
> obvious how much better the new synthesizer is than the old... See:
>
> https://www.nk7z.net/k3/
>
> for the screen shots.
>
> 73, and thanks,
> Dave (NK7Z)
> https://www.nk7z.net
> ARRL Volunteer Examiner
> ARRL Technical Specialist
> ARRL Asst. Director, NW Division, Technical Resources
>
> On 4/24/20 1:03 PM, Frank O'Donnell wrote:
> > Dave,
> >
> > Thanks, that may have been the thread I was remembering.
> >
> > While searching old messages, I also came across a post from Ed Cole
> > KL7UW from June 2018 in which he stated that, even if an external
> > reference is connected, the K3 frequency "is established by the
> > [internal] TCXO and the external reference merely performs a periodic
> > check. ... the EXREF system does not phase-lock the TCXO. It
> > periodically corrects the error but the TCXO drifts normally between
> > freg corrections ... . Now if you want to know why Elecraft chose
> > periodic freq correction over true phase-locking, the answer is low LO
> > phase noise. Much harder to get low phase noise in a PLL than in a
> TCXO."
> >
> > 73,
> >
> > Frank K6FOD
> >
> >
> > On 4/24/20 12:37 PM, Dave Cole wrote:
> >> Hi,
> >>
> >> That was me... I used to use my Icom 756 Pro, to watch the Doppler on
> >> changes in the ionosphere, and on Meteors. The K3 uses steps to
> >> correct frequency, while the Icom did not. Analog vs. Digital
> >> corrections.
> >>
> >> Accuracy is not an issue, it is the steps... They destroy the
> >> continuity of the tracking... I should have some captures if you are
> >> interested. Email me off list and I'll send a set.
> >>
> >> The issue for me, I am looking for changes in frequency, on the order
> >> of sub-1 hz., not looking to get an exact reading on the frequency,
> >> just changes in frequency across minutes, not days or hours.
> >>
> >> I don't need to be dead on for frequency, but I do need to have a
> >> straight line that is affected by Doppler, and path changes. I can't
> >> get that with my K3 without those annoying steps.
> >>
> >> Keep in mind we are talking worst case 6 or 10 Hz., and the steps
> >> appear to be far, far, smaller than that...
> >>
> >> So... I have given this aspect of the hobby up. I did just get the
> >> TXCO installed along with a lot of extras on my K3, and the steps are
> >> longer, but still there... I will get some older rig that is analog
> >> in nature and return to that aspect of the hobby then...
> >>
> >> I was able to watch echos from aircraft between Eugene, and Portland
> >> Oregon, (about 100 miles apart), using the KGW TV, (Ch. 2), aural
> >> carrier as a source. I got the coolest traces of Doppler shifts
> >> caused by the aircraft movement. Meteors were far more
> >> interesting... Anyway, it is not an issue of Frequency accuracy, bit
> >> one of how the rig makes adjustments. I would love to just turn off
> >> the steps, and accept the drift over longer times. Oh well... Hope
> >> that helps... It is NOT the K3 having an issue with measuring
> >> frequency...
> >>
> >> 73, and thanks,
> >> Dave (NK7Z)
> >>
> >> On 4/24/20 10:11 AM, Frank O'Donnell wrote:
> >>> Sometime (probably last year) I remember seeing a discussion of why
> >>> the K3/K3S receiver isn't suitable to do high-precision frequency
> >>> measurement tests at the level of hundredths of a Hertz. As I vaguely
> >>> recall, the receiver is designed so that its frequency actually
> >>> varies a bit intentionally, and I remember someone posting a plot
> >>> demonstrating this. However, I'm striking out on finding any of those
> >>> posts. Can anyone either help with them, or point to any other
> >>> discussion/explanation on this?
> >>>
> >>> Thanks much,
> >>>
> >>> Frank K6FOD
> >
> > ______________________________________________________________
> > 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
> > Message delivered to [hidden email]
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

alorona

Re: K3/K3S receiver and high-precision frequencydetermination?

In reply to this post by Wes Stewart-2

It's a good thing I didn't carry through on my plan to operate the K3 with a paper in the place of the top cover! That was a close call.

Seriously, don't *all* DDSs/PLLs/synthesizers/SDRs (and, thus, all modern transceivers) tune in steps? How is the tuning step related to the stability of an oscillator? I'll answer that: it isn't.

Al W6LX

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donovanf

Re: K3/K3S receiver and high-precision frequency determination?

In reply to this post by NK7Z

In 1969 -- right out of college and in my first EE job, I was tasked to
evaluate the technical performance of Sylvania's new R-1414 receiver
that was designed and manufactured to be the replacement for thousands
of R-390 and R-390A receivers then very widely used by the U.S. military.
It seemed like an easy low risk assignment for this newly minted
2nd Lieutentant under the supervision of my very experienced senior EE
boss, who coincidentally was a PVRC member (W3GN SK).

A few hundred R-1414s had been built for evaluation mostly by R-390
users prior to full scale production. R-390 users used it almost
exclusively for CW Morse, FSK RTTY and SSB voice. Without
exception all of their user evaluations came in very positive. My boss
W3GN was very pleased as were his superiors.

www.myvintagetv.com/posts/r1414.jpg

Everything was looking good during my technical evaluations until I
decided -- on my own initiative -- to set up a bit-error test using a
12 channel orthogonal frequency-division multiplex (OFDM) modem
(a high tech HF modem in 1969) modulating an SSB signal generator then
feeding the antenna input of t he R-1414. The audio output of the R-1414
then fed back into the OFDM modem. I used a nifty new DEC PDP-8
minicomputer (remember them?) to evaluate the bit-error performance
of the OFDM signal passing through the R-1414.

Much to my surprise I could never get better than a 0.1 percent error rate
no matter how I configured the R-1414 and no matter how ideal the SNR
was.

I managed to borrow a brand new Collins 651S-1 receiver from another
laboratory and -- much to my surprise -- that receiver easily achieved
orders of magnitude fewer errors, just as you would expect. W3GN's
superiors were very, very unhappy with my test report... I'm sure my work
would have been blown off had a ham not been my boss.

So why couldn't the R-1414 achieve acceptable error rates with OFDM
signals? To make a long story short, a design decision had been made to
use automatic frequency control (AFC) to control the R-1414 master oscillator.
The AFC operated several times per second, causing phase discontinuities
in the OFDM signal. On the other hand, the Collins 651S-1 used a
very well designed phase locked loop that caused no apparent bit errors
at all. The AFC scheme was so fundamental to the design of the R-1414
that a fix was impossible.

To make a long story short, the military's plan to purchase thousands of
of Sylvania R-1414s was scuttled by the technical work of a barely
21 year old 2nd Lieutenant. R-390s continued to be used for another
ten years and several thousand Collins 651S-1s and other commercial
HF receivers were purchased in the interim until the R-390 and other
interim receivers were finally replaced by thousands of Racal RA6790/GM
receivers starting in 1980.

radioaficion.com/HamNews/images/02-2012/ra6790gm_4-20120212191732.jpg

Thankfully the frequency jumps in the K3 are much less frequent than in
the R-1414 and apparently do not cause problems for digital signals.

73
Frank
W3LPL

----- Original Message -----

From: "Dave Cole" <[hidden email]>
To: [hidden email], [hidden email]
Sent: Friday, April 24, 2020 9:23:28 PM
Subject: Re: [Elecraft] K3/K3S receiver and high-precision frequency determination?

With the TXO on the order of one every few minutes, without on the order
two a minute or so.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 4/24/20 2:15 PM, [hidden email] wrote:

NK7Z

Re: K3/K3S receiver and high-precision frequency determination?

What a fascinating story! Thank you for sharing.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 4/24/20 4:35 PM, [hidden email] wrote:
> In 1969 -- right out of college...
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