HP E1938A oven alarm
Hi,
I want to use my E1938A to build a GPSDO. To be sure the 10MHz output is 'reliable' I have some LED indicators (e.g. GPS 3D fix and PLL lock) in mind.
Another parameter that is important is a stable temperature of the crystal. As far as I know there is no way to see if the oven has reached its required temperature, so I thought about making an oven monitor. See attached picture, on the left a part of the E1938A and on the right a window comparator.
If the LED goes on the temperature is either too low or too high. According to me it can simply be done by the way I 'designed' this.
Is it useful, or is there another way to be sure if the oven temperature on its required point? Or does a real time-nut just trust the E1938A with his eyes closed? 😉
By the way, has anyone here ever build a GPSDO with this unit?
BR, Rob
Hi
Simple answer is to keep it simple:
Put in a timer if you want to wait out the immediate warmup effects. Past that, your “out of lock” circuits on a GPSDO will detect an off temperature oven far faster than any other approach.
Bob
On Mar 13, 2025, at 5:05 PM, Rob040 . via time-nuts time-nuts@lists.febo.com wrote:
Hi,
I want to use my E1938A to build a GPSDO. To be sure the 10MHz output is 'reliable' I have some LED indicators (e.g. GPS 3D fix and PLL lock) in mind.
Another parameter that is important is a stable temperature of the crystal. As far as I know there is no way to see if the oven has reached its required temperature, so I thought about making an oven monitor. See attached picture, on the left a part of the E1938A and on the right a window comparator.
If the LED goes on the temperature is either too low or too high. According to me it can simply be done by the way I 'designed' this.
Is it useful, or is there another way to be sure if the oven temperature on its required point? Or does a real time-nut just trust the E1938A with his eyes closed? 😉
By the way, has anyone here ever build a GPSDO with this unit?
BR, Rob
<13-3-2025 18-17-04.jpg>_______________________________________________
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Hi Rob & Bob,
Sorry, I am a little late on the reply. My E1938 has two outputs, a watchdog and a heater. I just powered it up this morning to provide you an answer. The watchdog, as expected blinks at a 1 second(?) rate. The heater was solid for about ten minutes (again, approx.), and then it went out. I am assuming the heater output is based on target temperature. All I did was put the E1938 in a box and hooked up the indicated outputs.
The E1938 PUCK connector has a thermistor bridge output and the htr control/status is generated on the main board. The main board does not output these statuses to the DB25 conn. I simply hooked up to the main board LEDs. Due to attachment restrictions I will send a few E1938A docs and pictures directly.
Hope this helps a bit.
(The other) Bob
-----Original Message-----
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Thursday, March 13, 2025 5:37 PM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: HP E1938A oven alarm
Importance: High
Hi
Simple answer is to keep it simple:
Put in a timer if you want to wait out the immediate warmup effects. Past that, your “out of lock” circuits on a GPSDO will detect an off temperature oven far faster than any other approach.
Bob
On Mar 13, 2025, at 5:05 PM, Rob040 . via time-nuts time-nuts@lists.febo.com wrote:
Hi,
I want to use my E1938A to build a GPSDO. To be sure the 10MHz output is 'reliable' I have some LED indicators (e.g. GPS 3D fix and PLL lock) in mind.
Another parameter that is important is a stable temperature of the crystal. As far as I know there is no way to see if the oven has reached its required temperature, so I thought about making an oven monitor. See attached picture, on the left a part of the E1938A and on the right a window comparator.
If the LED goes on the temperature is either too low or too high. According to me it can simply be done by the way I 'designed' this.
Is it useful, or is there another way to be sure if the oven
temperature on its required point? Or does a real time-nut just trust
the E1938A with his eyes closed? 😉
By the way, has anyone here ever build a GPSDO with this unit?
BR, Rob
<13-3-2025
18-17-04.jpg>_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
an email to time-nuts-leave@lists.febo.com
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Hi Bob,
Thank you for the documents and pictures! Never guessed that there is already an 'oven ready' LED on the main board, also didn't pay attention to it when I first powered it up on arrival to check if the unit was working properly.
I searched for the meaning of all LED's and only found questions asked, but no answers.
That LED is actually what I had in mind: an indicator to know whether the OCXO has reached its final temperature and secondly detect failures during use. I dropped the latter requirement; Bob C. convinced me it's pretty useless.
So, I can conclude now that I can save myself an op-amp and some resistors.
I assume you only use the OCXO as standalone, no GNSS disciplined oscillator, correct? I am interested in that because of the low-pass filter after the PLL. That has to be calculated especially for the E1938A, at least what I understood. Not sure how precise that has to be, maybe trial & error will bring me an accurate 10MHz already.
Cheers, Rob
-----Oorspronkelijk bericht-----
Van: rbenward--- via time-nuts time-nuts@lists.febo.com
Verzonden: maandag 17 maart 2025 19:24
Aan: 'Discussion of precise time and frequency measurement' time-nuts@lists.febo.com
CC: rbenward@verizon.net
Onderwerp: [time-nuts] Re: HP E1938A oven alarm
Hi Rob & Bob,
Sorry, I am a little late on the reply. My E1938 has two outputs, a watchdog and a heater. I just powered it up this morning to provide you an answer. The watchdog, as expected blinks at a 1 second(?) rate. The heater was solid for about ten minutes (again, approx.), and then it went out. I am assuming the heater output is based on target temperature. All I did was put the E1938 in a box and hooked up the indicated outputs.
The E1938 PUCK connector has a thermistor bridge output and the htr control/status is generated on the main board. The main board does not output these statuses to the DB25 conn. I simply hooked up to the main board LEDs. Due to attachment restrictions I will send a few E1938A docs and pictures directly.
Hope this helps a bit.
(The other) Bob
-----Original Message-----
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Thursday, March 13, 2025 5:37 PM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: HP E1938A oven alarm
Importance: High
Hi
Simple answer is to keep it simple:
Put in a timer if you want to wait out the immediate warmup effects. Past that, your “out of lock” circuits on a GPSDO will detect an off temperature oven far faster than any other approach.
Bob
On Mar 13, 2025, at 5:05 PM, Rob040 . via time-nuts time-nuts@lists.febo.com wrote:
Hi,
I want to use my E1938A to build a GPSDO. To be sure the 10MHz output is 'reliable' I have some LED indicators (e.g. GPS 3D fix and PLL lock) in mind.
Another parameter that is important is a stable temperature of the crystal. As far as I know there is no way to see if the oven has reached its required temperature, so I thought about making an oven monitor. See attached picture, on the left a part of the E1938A and on the right a window comparator.
If the LED goes on the temperature is either too low or too high. According to me it can simply be done by the way I 'designed' this.
Is it useful, or is there another way to be sure if the oven
temperature on its required point? Or does a real time-nut just trust
the E1938A with his eyes closed? 😉
By the way, has anyone here ever build a GPSDO with this unit?
BR, Rob
<13-3-2025
18-17-04.jpg>_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
an email to time-nuts-leave@lists.febo.com
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Hi
If you are doing any sort of locked oscillator, the parameters and noise transfer characteristics of the “filter” are quite important. Whatever your “reference” is, it typically is noisy. Your OCXO is “quiet” (at some offsets). The purpose of the filter is to optimize the combined result. You want as much of the “quiet” from the OCXO as possible. You want to get the “more stable” from your reference without getting a lot of noise.
Fun !!!
Bob
On Mar 17, 2025, at 4:23 PM, Rob040 . via time-nuts time-nuts@lists.febo.com wrote:
Hi Bob,
Thank you for the documents and pictures! Never guessed that there is already an 'oven ready' LED on the main board, also didn't pay attention to it when I first powered it up on arrival to check if the unit was working properly.
I searched for the meaning of all LED's and only found questions asked, but no answers.
That LED is actually what I had in mind: an indicator to know whether the OCXO has reached its final temperature and secondly detect failures during use. I dropped the latter requirement; Bob C. convinced me it's pretty useless.
So, I can conclude now that I can save myself an op-amp and some resistors.
I assume you only use the OCXO as standalone, no GNSS disciplined oscillator, correct? I am interested in that because of the low-pass filter after the PLL. That has to be calculated especially for the E1938A, at least what I understood. Not sure how precise that has to be, maybe trial & error will bring me an accurate 10MHz already.
Cheers, Rob
-----Oorspronkelijk bericht-----
Van: rbenward--- via time-nuts time-nuts@lists.febo.com
Verzonden: maandag 17 maart 2025 19:24
Aan: 'Discussion of precise time and frequency measurement' time-nuts@lists.febo.com
CC: rbenward@verizon.net
Onderwerp: [time-nuts] Re: HP E1938A oven alarm
Hi Rob & Bob,
Sorry, I am a little late on the reply. My E1938 has two outputs, a watchdog and a heater. I just powered it up this morning to provide you an answer. The watchdog, as expected blinks at a 1 second(?) rate. The heater was solid for about ten minutes (again, approx.), and then it went out. I am assuming the heater output is based on target temperature. All I did was put the E1938 in a box and hooked up the indicated outputs.
The E1938 PUCK connector has a thermistor bridge output and the htr control/status is generated on the main board. The main board does not output these statuses to the DB25 conn. I simply hooked up to the main board LEDs. Due to attachment restrictions I will send a few E1938A docs and pictures directly.
Hope this helps a bit.
(The other) Bob
-----Original Message-----
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Thursday, March 13, 2025 5:37 PM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: HP E1938A oven alarm
Importance: High
Hi
Simple answer is to keep it simple:
Put in a timer if you want to wait out the immediate warmup effects. Past that, your “out of lock” circuits on a GPSDO will detect an off temperature oven far faster than any other approach.
Bob
On Mar 13, 2025, at 5:05 PM, Rob040 . via time-nuts time-nuts@lists.febo.com wrote:
Hi,
I want to use my E1938A to build a GPSDO. To be sure the 10MHz output is 'reliable' I have some LED indicators (e.g. GPS 3D fix and PLL lock) in mind.
Another parameter that is important is a stable temperature of the crystal. As far as I know there is no way to see if the oven has reached its required temperature, so I thought about making an oven monitor. See attached picture, on the left a part of the E1938A and on the right a window comparator.
If the LED goes on the temperature is either too low or too high. According to me it can simply be done by the way I 'designed' this.
Is it useful, or is there another way to be sure if the oven
temperature on its required point? Or does a real time-nut just trust
the E1938A with his eyes closed? 😉
By the way, has anyone here ever build a GPSDO with this unit?
BR, Rob
<13-3-2025
18-17-04.jpg>_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com _______________________________________________
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Rob,
I don't think I will turn the E1938A into a GPSDO. I already have a Trimble, a Z3801A, and a Z3805A. There are a few E1938A out there on Ebay, so maybe in the future, but not today. I am waiting for Synergy's GPS replacement to come in. That will modify one of the "Zs". If the improvement is worth it, I may upgrade the other Z.
I also made some PCBs to accommodate alternate OXCOs, including circuitry to invert the EFC. One of those alternate PCBs allows you to use your 10811 without the double oven, both the feedthrough version and the SMB version. As argued on this groups, the double oven may be overkill if the GPSDO is in your temperature stabilized house. The alternate board will accommodate a Oscilloquartz 8663 and a morion MV89, as well as others. Having solder pads for connections, it's a convenient board to use to experiment with other OXCOs. When I am done playing I may get rid of the excess boards I don't need.
Bob
-----Original Message-----
From: Rob040 . via time-nuts time-nuts@lists.febo.com
Sent: Monday, March 17, 2025 4:23 PM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: rbenward@verizon.net; Rob040 . rob040@live.nl
Subject: [time-nuts] Re: HP E1938A oven alarm
Importance: High
Hi Bob,
Thank you for the documents and pictures! Never guessed that there is already an 'oven ready' LED on the main board, also didn't pay attention to it when I first powered it up on arrival to check if the unit was working properly.
I searched for the meaning of all LED's and only found questions asked, but no answers.
That LED is actually what I had in mind: an indicator to know whether the OCXO has reached its final temperature and secondly detect failures during use. I dropped the latter requirement; Bob C. convinced me it's pretty useless.
So, I can conclude now that I can save myself an op-amp and some resistors.
I assume you only use the OCXO as standalone, no GNSS disciplined oscillator, correct? I am interested in that because of the low-pass filter after the PLL. That has to be calculated especially for the E1938A, at least what I understood. Not sure how precise that has to be, maybe trial & error will bring me an accurate 10MHz already.
Cheers, Rob
-----Oorspronkelijk bericht-----
Van: rbenward--- via time-nuts time-nuts@lists.febo.com
Verzonden: maandag 17 maart 2025 19:24
Aan: 'Discussion of precise time and frequency measurement' time-nuts@lists.febo.com
CC: rbenward@verizon.net
Onderwerp: [time-nuts] Re: HP E1938A oven alarm
Hi Rob & Bob,
Sorry, I am a little late on the reply. My E1938 has two outputs, a watchdog and a heater. I just powered it up this morning to provide you an answer. The watchdog, as expected blinks at a 1 second(?) rate. The heater was solid for about ten minutes (again, approx.), and then it went out. I am assuming the heater output is based on target temperature. All I did was put the E1938 in a box and hooked up the indicated outputs.
The E1938 PUCK connector has a thermistor bridge output and the htr control/status is generated on the main board. The main board does not output these statuses to the DB25 conn. I simply hooked up to the main board LEDs. Due to attachment restrictions I will send a few E1938A docs and pictures directly.
Hope this helps a bit.
(The other) Bob
-----Original Message-----
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Thursday, March 13, 2025 5:37 PM
To: Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Cc: Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: HP E1938A oven alarm
Importance: High
Hi
Simple answer is to keep it simple:
Put in a timer if you want to wait out the immediate warmup effects. Past that, your “out of lock” circuits on a GPSDO will detect an off temperature oven far faster than any other approach.
Bob
On Mar 13, 2025, at 5:05 PM, Rob040 . via time-nuts time-nuts@lists.febo.com wrote:
Hi,
I want to use my E1938A to build a GPSDO. To be sure the 10MHz output is 'reliable' I have some LED indicators (e.g. GPS 3D fix and PLL lock) in mind.
Another parameter that is important is a stable temperature of the crystal. As far as I know there is no way to see if the oven has reached its required temperature, so I thought about making an oven monitor. See attached picture, on the left a part of the E1938A and on the right a window comparator.
If the LED goes on the temperature is either too low or too high. According to me it can simply be done by the way I 'designed' this.
Is it useful, or is there another way to be sure if the oven
temperature on its required point? Or does a real time-nut just trust
the E1938A with his eyes closed? 😉
By the way, has anyone here ever build a GPSDO with this unit?
BR, Rob
<13-3-2025
18-17-04.jpg>_______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com _______________________________________________
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com _______________________________________________
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