Shielding a DAC line
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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Hi Bob,
If you've got a stable SSB receiver and an AM receiver capable of 20MHz, here's a trick to get an accurate beat: Tune both to WWV, and listen to the WWV generated tone. Adjust the frequency on your SSB receiver to exactly beat the tone on the AM receiver. That way, you're matching a tone, and not a fading carrier. Then adjust your 20MHz oscillator to zero-beat your SSB receiver. If you have a good ear, it should get you down there to less than 1Hz of error.
But, if you are hooked enough to ask the question, you are probably hooked enough to eventually buy both GPSDO and Rb standard. Ask me how I know. =) There are numerous GPSDOs out there that you can build or buy complete. I'm currently rewriting much of Bert, VE2ZAZ's GPSDO code. Another programmer is "joining the staff" as well. With a case, a PSU, an OCXO, a board and chip from Bert to start with, and the usual misc parts, you can join the fun. (I do not sell parts or code or programmed chips. This is a hobby for me, not a money-making scheme.) Or you could go the standard route with the more traditional bought parts which might turn out cheaper in the long run. Cases etc are just so expensive these days.
I'm a newbie time nut, so take the above with a grain of salt.
Bob - AE6RV
From: Bob Albert bob91343@yahoo.com
To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 8:24 PM
Subject: Re: [time-nuts] Shielding a DAC line
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV
higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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Hi Bob,
You say you are not ready to go GPS. I assume you mean a GPSDO. If you have a 'scope you can use just about any GPS with a 1pps output. trigger the scope from the 1pps while monitoring the 20MHz sine wave and adjust for minimum drift of the trace. A timing GPS module will be better (you can get a used Oncore UT plus for under $20 on ebay) but anything will be better than beating an HF signal by ear.
HTH,
Robert G8RPI. (too many Bobs :-)
From: Bob Albert bob91343@yahoo.com
To: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, 27 September 2013, 2:24
Subject: Re: [time-nuts] Shielding a DAC line
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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Hi
One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close as you are likely to get in terms of carrier accuracy over HF radio.
To do better, you would need to go to the time domain. Generate a tick off of your oscillator(s) and compare it to the time tick on the radio. Compared over a time span of days you can improve your accuracy.
Bob
On Sep 26, 2013, at 9:24 PM, Bob Albert bob91343@yahoo.com wrote:
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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Ah that time tick idea makes sense. Now I just have to figure out how to generate it from my time base. And of course, since I don't want to stay awake for several days, I am worried about missing counts on the comparison. Did that move up, or down? And I would need to control which part of the cycle to compare so that I can listen to the ticks trying to be in synchronization.
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 4:30 AM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close as you are likely to get in terms of carrier accuracy over HF radio.
To do better, you would need to go to the time domain. Generate a tick off of your oscillator(s) and compare it to the time tick on the radio. Compared over a time span of days you can improve your accuracy.
Bob
On Sep 26, 2013, at 9:24 PM, Bob Albert bob91343@yahoo.com wrote:
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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I invented (?) a system for HF calibration against WWV.
The 20 MHz signal is too weak to be useful. So I am using 15 MHz. I have my signal generator set at 15 MHz and hear a slow beat against WWV (watching S meter on TS-940S in AM mode).
I raise the generator frequency by 1 Hz and note the faster beat. I then lower it by 1 Hz and note a different speed beat. If the two beats are the same speed, the generator is on frequency. One of course will be slower, and that's closer than the faster one. If I adjust the frequency of the generator master oscillator I should be able to nail it within maybe 1/4 Hz, representing an error of 1 part in 60 million, or 16 ppb. Neglecting propagation effects of course, which aren't too erratic. And I'm not trying to learn the right time, just the right frequency, so propagation won't be important as long as the beats aren't varying.
What do you think?
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 4:30 AM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close as you are likely to get in terms of carrier accuracy over HF radio.
To do better, you would need to go to the time domain. Generate a tick off of your oscillator(s) and compare it to the time tick on the radio. Compared over a time span of days you can improve your accuracy.
Bob
On Sep 26, 2013, at 9:24 PM, Bob Albert bob91343@yahoo.com wrote:
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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I invented (?) a system for HF calibration against WWV.
The 20
MHz signal is too weak to be useful. So I am using 15 MHz. I have my
signal generator set at 15 MHz and hear a slow beat against WWV
(watching S meter on TS-940S in AM mode).
I raise the generator
frequency by 1 Hz and note the faster beat. I then lower it by 1 Hz and
note a different speed beat. If the two beats are the same speed, the
generator is on frequency. One of course will be slower, and that's
closer than the faster one. If I adjust the frequency of the generator
master oscillator I should be able to nail it within maybe 1/4 Hz,
representing an error of 1 part in 60 million, or 16 ppb. Neglecting
propagation effects of course, which aren't too erratic. And I'm not
trying to learn the right time, just the right frequency, so propagation
won't be important as long as the beats aren't varying.
What do you think?
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 4:30 AM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close as you are likely to get in terms of carrier accuracy over HF radio.
To do better, you would need to go to the time domain. Generate a tick off of your oscillator(s) and compare it to the time tick on the radio. Compared over a time span of days you can improve your accuracy.
Bob
On Sep 26, 2013, at 9:24 PM, Bob Albert bob91343@yahoo.com wrote:
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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Hi
If you already know that the standard is within 50 ppb, then it only can drift 50 nanoseconds per second. If you check it every 100,000 seconds (a bit more than a day), it can not have slipped more than 5,000,000 nanoseconds. You still will be within 0.005 ms of the time tick. Even after 20 days there's no real ambiguity relative to the tick.
All you do is to put the audio from WWV up on a 'scope and trigger off of the tick from your OCXO. As the tone moves back and forth on the screen you can estimate what's going on. You need to do it same time each day and try to avoid sunrise / sunset issues. You want as consistent a propagation path as possible between you and the transmitter.
Bob
On Sep 27, 2013, at 11:58 AM, Bob Albert bob91343@yahoo.com wrote:
Ah that time tick idea makes sense. Now I just have to figure out how to generate it from my time base. And of course, since I don't want to stay awake for several days, I am worried about missing counts on the comparison. Did that move up, or down? And I would need to control which part of the cycle to compare so that I can listen to the ticks trying to be in synchronization.
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 4:30 AM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close as you are likely to get in terms of carrier accuracy over HF radio.
To do better, you would need to go to the time domain. Generate a tick off of your oscillator(s) and compare it to the time tick on the radio. Compared over a time span of days you can improve your accuracy.
Bob
On Sep 26, 2013, at 9:24 PM, Bob Albert bob91343@yahoo.com wrote:
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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I just did what I consider to be the best calibration possible without getting more equipment. I adjusted my generator to be within 0.25 Hz of 15 MHz WWV. Then I matched my counter to the generator at 520 MHz, within about 2 or 3 Hz. I am satisfied that nobody is going to call me out of tune.
I am impressed with the ease of working with this gear, both units HP but decades old.
Thanks for your help. If I get a GPS or rubidium unit I will take it farther. (The GPS units require antennas and connectors I don't have, plus software and computer interface, too much trouble right now.)
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 1:11 PM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
If you already know that the standard is within 50 ppb, then it only can drift 50 nanoseconds per second. If you check it every 100,000 seconds (a bit more than a day), it can not have slipped more than 5,000,000 nanoseconds. You still will be within 0.005 ms of the time tick. Even after 20 days there's no real ambiguity relative to the tick.
All you do is to put the audio from WWV up on a 'scope and trigger off of the tick from your OCXO. As the tone moves back and forth on the screen you can estimate what's going on. You need to do it same time each day and try to avoid sunrise / sunset issues. You want as consistent a propagation path as possible between you and the transmitter.
Bob
On Sep 27, 2013, at 11:58 AM, Bob Albert bob91343@yahoo.com wrote:
Ah that time tick idea makes sense. Now I just have to figure out how to generate it from my time base. And of course, since I don't want to stay awake for several days, I am worried about missing counts on the comparison. Did that move up, or down? And I would need to control which part of the cycle to compare so that I can listen to the ticks trying to be in synchronization.
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 4:30 AM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close as you are likely to get in terms of carrier accuracy over HF radio.
To do better, you would need to go to the time domain. Generate a tick off of your oscillator(s) and compare it to the time tick on the radio. Compared over a time span of days you can improve your accuracy.
Bob
On Sep 26, 2013, at 9:24 PM, Bob Albert bob91343@yahoo.com wrote:
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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Hi
Anything under 100 ppb relative to WWVB is probably closer than the ionosphere will let you get under normal conditions. You can indeed get a zero beat, but that's not always a guarantee that the carrier isn't moving around at some odd rate. Far better to use WWVB. The LF path is much more predictable, so you can pick "good" times to check it each day. After a few days you can have some pretty good information.
Bob
On Sep 27, 2013, at 4:26 PM, Bob Albert bob91343@yahoo.com wrote:
I just did what I consider to be the best calibration possible without getting more equipment. I adjusted my generator to be within 0.25 Hz of 15 MHz WWV. Then I matched my counter to the generator at 520 MHz, within about 2 or 3 Hz. I am satisfied that nobody is going to call me out of tune.
I am impressed with the ease of working with this gear, both units HP but decades old.
Thanks for your help. If I get a GPS or rubidium unit I will take it farther. (The GPS units require antennas and connectors I don't have, plus software and computer interface, too much trouble right now.)
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 1:11 PM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
If you already know that the standard is within 50 ppb, then it only can drift 50 nanoseconds per second. If you check it every 100,000 seconds (a bit more than a day), it can not have slipped more than 5,000,000 nanoseconds. You still will be within 0.005 ms of the time tick. Even after 20 days there's no real ambiguity relative to the tick.
All you do is to put the audio from WWV up on a 'scope and trigger off of the tick from your OCXO. As the tone moves back and forth on the screen you can estimate what's going on. You need to do it same time each day and try to avoid sunrise / sunset issues. You want as consistent a propagation path as possible between you and the transmitter.
Bob
On Sep 27, 2013, at 11:58 AM, Bob Albert bob91343@yahoo.com wrote:
Ah that time tick idea makes sense. Now I just have to figure out how to generate it from my time base. And of course, since I don't want to stay awake for several days, I am worried about missing counts on the comparison. Did that move up, or down? And I would need to control which part of the cycle to compare so that I can listen to the ticks trying to be in synchronization.
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 4:30 AM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close as you are likely to get in terms of carrier accuracy over HF radio.
To do better, you would need to go to the time domain. Generate a tick off of your oscillator(s) and compare it to the time tick on the radio. Compared over a time span of days you can improve your accuracy.
Bob
On Sep 26, 2013, at 9:24 PM, Bob Albert bob91343@yahoo.com wrote:
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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Well I did this calibration around noon so the ionosphere was about as stable as it gets. In any case, I am satisfied.
However, you bring up WWVB. How can I utilize that? Do I need to build a receiver? I do have some ham gear that will receive there but signals aren't so good.
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 1:35 PM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
Anything under 100 ppb relative to WWVB is probably closer than the ionosphere will let you get under normal conditions. You can indeed get a zero beat, but that's not always a guarantee that the carrier isn't moving around at some odd rate. Far better to use WWVB. The LF path is much more predictable, so you can pick "good" times to check it each day. After a few days you can have some pretty good information.
Bob
On Sep 27, 2013, at 4:26 PM, Bob Albert bob91343@yahoo.com wrote:
I just did what I consider to be the best calibration possible without getting more equipment. I adjusted my generator to be within 0.25 Hz of 15 MHz WWV. Then I matched my counter to the generator at 520 MHz, within about 2 or 3 Hz. I am satisfied that nobody is going to call me out of tune.
I am impressed with the ease of working with this gear, both units HP but decades old.
Thanks for your help. If I get a GPS or rubidium unit I will take it farther. (The GPS units require antennas and connectors I don't have, plus software and computer interface, too much trouble right now.)
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 1:11 PM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
If you already know that the standard is within 50 ppb, then it only can drift 50 nanoseconds per second. If you check it every 100,000 seconds (a bit more than a day), it can not have slipped more than 5,000,000 nanoseconds. You still will be within 0.005 ms of the time tick. Even after 20 days there's no real ambiguity relative to the tick.
All you do is to put the audio from WWV up on a 'scope and trigger off of the tick from your OCXO. As the tone moves back and forth on the screen you can estimate what's going on. You need to do it same time each day and try to avoid sunrise / sunset issues. You want as consistent a propagation path as possible between you and the transmitter.
Bob
On Sep 27, 2013, at 11:58 AM, Bob Albert bob91343@yahoo.com wrote:
Ah that time tick idea makes sense. Now I just have to figure out how to generate it from my time base. And of course, since I don't want to stay awake for several days, I am worried about missing counts on the comparison. Did that move up, or down? And I would need to control which part of the cycle to compare so that I can listen to the ticks trying to be in synchronization.
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 4:30 AM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close as you are likely to get in terms of carrier accuracy over HF radio.
To do better, you would need to go to the time domain. Generate a tick off of your oscillator(s) and compare it to the time tick on the radio. Compared over a time span of days you can improve your accuracy.
Bob
On Sep 26, 2013, at 9:24 PM, Bob Albert bob91343@yahoo.com wrote:
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Hi
WWVB is at 60 KHz. If you have a radio that will tune down there and an antenna, you're set up. Things like wall clocks and wrist watches have miniature receivers in them that pull timing off of WWVB, so that's an option for parts if you aren't set up already.
WWB puts out a time code as AM modulation and as phase modulation on the carrier. Both can be compared to a local time tick. For greater accuracy, you can look at the carrier phase. Since they put in phase modulation that process has gotten a bit more complex. There are many threads here on the list going into all the various details.
Bob
On Sep 27, 2013, at 5:29 PM, Bob Albert bob91343@yahoo.com wrote:
Well I did this calibration around noon so the ionosphere was about as stable as it gets. In any case, I am satisfied.
However, you bring up WWVB. How can I utilize that? Do I need to build a receiver? I do have some ham gear that will receive there but signals aren't so good.
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 1:35 PM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
Anything under 100 ppb relative to WWVB is probably closer than the ionosphere will let you get under normal conditions. You can indeed get a zero beat, but that's not always a guarantee that the carrier isn't moving around at some odd rate. Far better to use WWVB. The LF path is much more predictable, so you can pick "good" times to check it each day. After a few days you can have some pretty good information.
Bob
On Sep 27, 2013, at 4:26 PM, Bob Albert bob91343@yahoo.com wrote:
I just did what I consider to be the best calibration possible without getting more equipment. I adjusted my generator to be within 0.25 Hz of 15 MHz WWV. Then I matched my counter to the generator at 520 MHz, within about 2 or 3 Hz. I am satisfied that nobody is going to call me out of tune.
I am impressed with the ease of working with this gear, both units HP but decades old.
Thanks for your help. If I get a GPS or rubidium unit I will take it farther. (The GPS units require antennas and connectors I don't have, plus software and computer interface, too much trouble right now.)
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 1:11 PM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
If you already know that the standard is within 50 ppb, then it only can drift 50 nanoseconds per second. If you check it every 100,000 seconds (a bit more than a day), it can not have slipped more than 5,000,000 nanoseconds. You still will be within 0.005 ms of the time tick. Even after 20 days there's no real ambiguity relative to the tick.
All you do is to put the audio from WWV up on a 'scope and trigger off of the tick from your OCXO. As the tone moves back and forth on the screen you can estimate what's going on. You need to do it same time each day and try to avoid sunrise / sunset issues. You want as consistent a propagation path as possible between you and the transmitter.
Bob
On Sep 27, 2013, at 11:58 AM, Bob Albert bob91343@yahoo.com wrote:
Ah that time tick idea makes sense. Now I just have to figure out how to generate it from my time base. And of course, since I don't want to stay awake for several days, I am worried about missing counts on the comparison. Did that move up, or down? And I would need to control which part of the cycle to compare so that I can listen to the ticks trying to be in synchronization.
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Friday, September 27, 2013 4:30 AM
Subject: Re: [time-nuts] Shielding a DAC line -> WWV
Hi
One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close as you are likely to get in terms of carrier accuracy over HF radio.
To do better, you would need to go to the time domain. Generate a tick off of your oscillator(s) and compare it to the time tick on the radio. Compared over a time span of days you can improve your accuracy.
Bob
On Sep 26, 2013, at 9:24 PM, Bob Albert bob91343@yahoo.com wrote:
This is off topic but I'm unsure how to do it properly.
I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz WWV but can't tell the difference between fading and the beat, so I am stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think.
What can I do to take the next step to bring the oscillators in closer agreement? I am not ready to go GPS or buy a rubidium standard.
Bob
From: Bob Stewart bob@evoria.net
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 6:13 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi Bob,
I should have mentioned that I added a new 5MHz output, and the coax ran within 1/8" of the single DAC wire going to the OCXO. I don't think anything else changed, but of course there could be some flake of something on the DAC line that I missed. I put on the RG-174 and I see that it's still locking high. I suppose it could be just that it was a long power cycle to the oscillator. Come to think of it, this thing does like to move to a new voltage sometimes when I have it off to mess with something. So, maybe it's just the oscillator being cranky. I haven't had it off for more than just a few seconds in a long time. If I weren't in test and development mode where anomalies are good, I think I'd put the old one back in.
Thanks as always,
Bob
From: Bob Camp lists@rtty.us
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, September 26, 2013 7:54 PM
Subject: Re: [time-nuts] Shielding a DAC line
Hi
I suspect that you have a ground offset between the OCXO's ground return and the DAC's ground reference. The signal should be DC, Shielding it won't hurt, but it really should not help much. If anything is an issue a simple R/C filter at the OCXO pin should nuke it better than coax will.
Bob
On Sep 26, 2013, at 8:09 PM, Bob Stewart bob@evoria.net wrote:
I made some minor hardware changes to my GPSDO today and I see that it's locked to a new DAC voltage about 21mV higher. So, I was wondering about shielding the short run to the OCXO. I have immediately available RG-174 and I'm putting that in. But, should this be some sort of steel shelled semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask.
Bob - AE6RV
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