Re: [time-nuts] EFC divider resistors
To all those time-nuts (volt-nuts as well) who have been chatting about temperature controlled environments, here is my input. I found a very neat ready-built controlled oven at a number of hamfests in the southeast (Florida Alabama) that work quite well to enclose small circuits that need to be temperature controled I found them still being sold by Fair Radio (www.fairradio.com) for only $12 apiece. Schematic is included to increase their value to us hackers. Their catalog number is OSC-8004290G1. The outside dimensions of the box is 6.5x2x3.3 inches, with about 0.5 inches of insulation and inner enclosure. They were used in Army GRT-21/22 transmitters, and contain all the necessary temperature control circuitry, as well as a crystal oscillator. I bought a couple of these gems and removed the oscillator circuitry and had a nice oven assembly with enough room inside to house a lot of circuitry for just about any thing requiring close trmperature control. It's designed to run at 75C, but with a few resistor changes, the temperature can be lowered if desired. It's insulated pretty well, too. Not a power miser by any stretch, but it has lots of potential. Cheers, Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] time-nuts] EFC divider resistors progress
Hi Hendrik, My house is on a slab of concrete, so about 8 hours ago, I moved it from the top of the HP stack to the floor. The net phase error for the past 7 hours is about 180 degrees with no change to the DAC value. So, I think it's found a stable home. I'll put the low temp coeff resistors in when they come in, as well. BTW, it's in an old HP chassis, with the feet on, so the case isn't in hard contact with the floor. thanks, Bob From: Hendrik Dietrich don_he...@gmx.de To: b...@evoria.net Sent: Sunday, February 2, 2014 7:06 AM Subject: time-nuts] EFC divider resistors Hi Bob, consider putting the divider resistors close to a temperature-stable place: The outside of the oven. The thermal swings will already be smaller there, I guess BR Hendrik ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Hi OCXO’s with separate ground for the oven have indeed been made. They do show up in catalogs and on data sheets. Customers don’t buy them….. The same is true of the other approach, which is to bring out a separate (isolated) EFC return. Bob On Jan 31, 2014, at 11:14 PM, Hal Murray hmur...@megapathdsl.net wrote: li...@rtty.us said: A 7805 has a *rated* temperature coefficient of 2 mv / C. Most parts do way better than this. The problem is knowing if you have a good part or not. On a 5V part, your reference could be running 400 ppm/C. Since the divider has no impact on this number, it over-rides what ever you do with the divider resistors. A good voltage reference will set you back about $50 or so. Plan B would be to keep the 7805 at a constant temperature. You commonly see a couple of mv of variation in the ground pin voltage with oven current depending on exactly where the pin is terminated. Any change in the ground setup can be an issue on an OCXO with the EFC in common with the oven (which is most parts). Again, plan B would be to keep the OCXO at a constant temperature so the heater current is (close) to constant and the offset on the ground pin due to heater current would be constant. - I've heard comments about offset due to a single ground pin for several/many years, so it's nothing new. Why are manufacturers not providing separate pins? Are there OCXOs (that I haven't noticed) with 2 ground pins? Is the problem backward compatibility? In that case, I'd expect there would be a pinout with a new second-ground pin that offered an interesting beat-this challenge to other vendors. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] EFC divider resistors
All, The REF 102 from TI is a +10 reference with a TC of 2.5PPM/max. Using two 1% 50 PPM metal film Xcion resistors on can make a +5 V regulator that is far superior to a 7805. Cost is about $7 from mouser. If one needs to have an adjustable resistor in a circuit perhaps one of the digital pots that are available will suffice. A question: would thermal cycling oscillators or reference boards be useful before starting a stability run? Regards, Perrier ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] EFC divider resistors
I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
The problem is certainly real enough. What you're seeing is a drift of approx 2500ppm, and Vishay shows the temperature coefficient of their standard carbon film resistor, for example, to be approx 200ppm per degree C for a value of 20K. If yours is carbon film this would imply your measured resistor is seeing a temperature rise of around 10 or 12 degrees C, which might be a bit on the high side but is certainly feasible given a body temperature of around 35 degrees C. Standard metal film resistors have a lower temperature coefficient, say around 50ppm per degree C, so this might be one option for reducing the effect, another could be temperature control of your EFC network. There are more specialised resistors with much lower temeparature coefficients, the Vishay RCME series of metal film resistors for example can be as low as 5 to 6 ppm per degree C, although I don't know what the cost difference might be. And no, I don't have any shares in Vishay:-) Regards Nigel GM8PZR In a message dated 31/01/2014 17:04:24 GMT Standard Time, b...@evoria.net writes: I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse From: Bob Stewart b...@evoria.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 12:01 PM Subject: [time-nuts] EFC divider resistors I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Hi Nigel, I didn't give any thought to thermal issues when I bought the resistors. They're just standard carbon composition. I see some metal film resistors with a temp coefficient of 5 PPM/C, so I'll get some of those and put them in. thanks, Bob From: gandal...@aol.com gandal...@aol.com To: time-nuts@febo.com Sent: Friday, January 31, 2014 11:35 AM Subject: Re: [time-nuts] EFC divider resistors The problem is certainly real enough. What you're seeing is a drift of approx 2500ppm, and Vishay shows the temperature coefficient of their standard carbon film resistor, for example, to be approx 200ppm per degree C for a value of 20K. If yours is carbon film this would imply your measured resistor is seeing a temperature rise of around 10 or 12 degrees C, which might be a bit on the high side but is certainly feasible given a body temperature of around 35 degrees C. Standard metal film resistors have a lower temperature coefficient, say around 50ppm per degree C, so this might be one option for reducing the effect, another could be temperature control of your EFC network. There are more specialised resistors with much lower temeparature coefficients, the Vishay RCME series of metal film resistors for example can be as low as 5 to 6 ppm per degree C, although I don't know what the cost difference might be. And no, I don't have any shares in Vishay:-) Regards Nigel GM8PZR In a message dated 31/01/2014 17:04:24 GMT Standard Time, b...@evoria.net writes: I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
I just realized that I have a pot in the mix. I see one on Mouser with 25PPM/C, so I suppose I'll try that. Here's the circuit I'll use with the replacements. What I have in there now has the values of R3, R4, and R5 multiplied by 10 and R2 is 3.9K. I suppose it won't matter so much for the pot. http://www.evoria.net/AE6RV/GPSstd_PLL/EFC%20Divider/EFC2.png Bob From: Robert LaJeunesse rlajeune...@sbcglobal.net To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 11:40 AM Subject: Re: [time-nuts] EFC divider resistors Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse From: Bob Stewart b...@evoria.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 12:01 PM Subject: [time-nuts] EFC divider resistors I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
It's hard to be sure without knowing the characteristics of the DAC ouput and the oscillator EFC, but if you're only making a one off I wonder if it might perhaps be possible to simplify that arrangement to just a potential divider using selected values and being fed from the DAC and tapped off into the EFC? Regards Nigel GM8PZR In a message dated 31/01/2014 18:04:39 GMT Standard Time, b...@evoria.net writes: I just realized that I have a pot in the mix. I see one on Mouser with 25PPM/C, so I suppose I'll try that. Here's the circuit I'll use with the replacements. What I have in there now has the values of R3, R4, and R5 multiplied by 10 and R2 is 3.9K. I suppose it won't matter so much for the pot. http://www.evoria.net/AE6RV/GPSstd_PLL/EFC%20Divider/EFC2.png Bob From: Robert LaJeunesse rlajeune...@sbcglobal.net To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 11:40 AM Subject: Re: [time-nuts] EFC divider resistors Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse From: Bob Stewart b...@evoria.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 12:01 PM Subject: [time-nuts] EFC divider resistors I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
The ratio tempco is the point! It's hard to design a divider yourself, since temperature differences between the two divider resistors is the problem. Resistor networks with very low ratio tempcos are fairly expensive. I don't know your budget and how far you want to go. If you want to try it yourself, use voltage divider resistors of only one value and combine the required number of resistors. That is to have each resistor at the same power dissipation (and therefore at the same drift), then put them together very closely. Isolate them with insultation tape or so. Example: 10V to 2.5V: use 4 resistors of say 1k and pickup the 2.5 volts at the resistor next to ground. By the way: in a temperature sensitive environment where every microvolt counts I would not recommend using a potentiometer. Use it for determining the exact values and then replace the pot by the required number of resistors, see above. Tell us something about your intended budget. Volker Am 31.01.2014 18:40, schrieb Robert LaJeunesse: Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse From: Bob Stewart b...@evoria.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 12:01 PM Subject: [time-nuts] EFC divider resistors I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Here's how to place the divider resistors. The picture is from 1992, I didn't use SMDs then. But the results are promising at a very low price. Isolierband = insulation tape wärmeleit. Kern = thermoconducting core The picture shows two examples, the left one if you need three resistors, the right one if you need six. Use metal film types with low tempco. Keep in mind: it's the fluctuating _difference_ between the resistor values, that'll kill your stability. So avoid everything, that leads to different temperatures at the resistors. In particular avoid placing them into an airstream. Volker Am 31.01.2014 20:25, schrieb Volker Esper: The ratio tempco is the point! It's hard to design a divider yourself, since temperature differences between the two divider resistors is the problem. Resistor networks with very low ratio tempcos are fairly expensive. I don't know your budget and how far you want to go. If you want to try it yourself, use voltage divider resistors of only one value and combine the required number of resistors. That is to have each resistor at the same power dissipation (and therefore at the same drift), then put them together very closely. Isolate them with insultation tape or so. Example: 10V to 2.5V: use 4 resistors of say 1k and pickup the 2.5 volts at the resistor next to ground. By the way: in a temperature sensitive environment where every microvolt counts I would not recommend using a potentiometer. Use it for determining the exact values and then replace the pot by the required number of resistors, see above. Tell us something about your intended budget. Volker Am 31.01.2014 18:40, schrieb Robert LaJeunesse: Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse From: Bob Stewart b...@evoria.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 12:01 PM Subject: [time-nuts] EFC divider resistors I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Sorry, missing picture... Am 31.01.2014 20:47, schrieb Volker Esper: Here's how to place the divider resistors. The picture is from 1992, I didn't use SMDs then. But the results are promising at a very low price. Isolierband = insulation tape wärmeleit. Kern = thermoconducting core The picture shows two examples, the left one if you need three resistors, the right one if you need six. Use metal film types with low tempco. Keep in mind: it's the fluctuating _difference_ between the resistor values, that'll kill your stability. So avoid everything, that leads to different temperatures at the resistors. In particular avoid placing them into an airstream. Volker Am 31.01.2014 20:25, schrieb Volker Esper: The ratio tempco is the point! It's hard to design a divider yourself, since temperature differences between the two divider resistors is the problem. Resistor networks with very low ratio tempcos are fairly expensive. I don't know your budget and how far you want to go. If you want to try it yourself, use voltage divider resistors of only one value and combine the required number of resistors. That is to have each resistor at the same power dissipation (and therefore at the same drift), then put them together very closely. Isolate them with insultation tape or so. Example: 10V to 2.5V: use 4 resistors of say 1k and pickup the 2.5 volts at the resistor next to ground. By the way: in a temperature sensitive environment where every microvolt counts I would not recommend using a potentiometer. Use it for determining the exact values and then replace the pot by the required number of resistors, see above. Tell us something about your intended budget. Volker Am 31.01.2014 18:40, schrieb Robert LaJeunesse: Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse From: Bob Stewart b...@evoria.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 12:01 PM Subject: [time-nuts] EFC divider resistors I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. attachment: DF9PL_Resistor_devider.gif___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
I'm trying to put something together that is generic enough for the guys on the VE2ZAZ GPS Standard board, but that will be relatively free of temperature issues. Yeah, I know: an impossible task. The precision of the GPSDO is probably not in the same league as what this board is used to. The DAC is actually a 10-bit PWM with 4 bits of dither. The output from the board comes from an op-amp. The OCXO (for me) is a Trimble 34310-T. Its range across 0 to +5V is about 7.5Hz. I'm trying to reduce that to 2Hz. In spite of those limitations, it works well. I'm just trying to wring every last bit of performance out of it, but in a way that my results could be generally repeatable by someone who was willing to make a moderate effort. I didn't have any problem with finding 5PPM/C resistors for the 20K and 6.8k. The others were a different story. I found a 15PPM for the pot, and 5PPM and 10PPM for the others in values that should be close enough. I think I'll look around on Mouser a bit more before I press the buy button, but this is probably what I'll wind up getting. Bob From: gandal...@aol.com gandal...@aol.com To: time-nuts@febo.com Sent: Friday, January 31, 2014 1:18 PM Subject: Re: [time-nuts] EFC divider resistors It's hard to be sure without knowing the characteristics of the DAC ouput and the oscillator EFC, but if you're only making a one off I wonder if it might perhaps be possible to simplify that arrangement to just a potential divider using selected values and being fed from the DAC and tapped off into the EFC? Regards Nigel GM8PZR In a message dated 31/01/2014 18:04:39 GMT Standard Time, b...@evoria.net writes: I just realized that I have a pot in the mix. I see one on Mouser with 25PPM/C, so I suppose I'll try that. Here's the circuit I'll use with the replacements. What I have in there now has the values of R3, R4, and R5 multiplied by 10 and R2 is 3.9K. I suppose it won't matter so much for the pot. http://www.evoria.net/AE6RV/GPSstd_PLL/EFC%20Divider/EFC2.png Bob From: Robert LaJeunesse rlajeune...@sbcglobal.net To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 11:40 AM Subject: Re: [time-nuts] EFC divider resistors Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse From: Bob Stewart b...@evoria.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 12:01 PM Subject: [time-nuts] EFC divider resistors I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Hi Volker, Thanks for the ideas. The resistors are all within a short radius of each other. I hadn't thought about bundling them all together. I suppose I could epoxy them together as a last resort. I've got some EPF foam, so I could try putting that on the board right against them. In fact, I could try that while waiting for the new parts. I've already used foam to fill most of the space in the box, except for around and above the OCXO. From: Volker Esper ail...@t-online.de To: Robert LaJeunesse lajeune...@mail.com; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 1:51 PM Subject: Re: [time-nuts] EFC divider resistors Sorry, missing picture... Am 31.01.2014 20:47, schrieb Volker Esper: Here's how to place the divider resistors. The picture is from 1992, I didn't use SMDs then. But the results are promising at a very low price. Isolierband = insulation tape wärmeleit. Kern = thermoconducting core The picture shows two examples, the left one if you need three resistors, the right one if you need six. Use metal film types with low tempco. Keep in mind: it's the fluctuating _difference_ between the resistor values, that'll kill your stability. So avoid everything, that leads to different temperatures at the resistors. In particular avoid placing them into an airstream. Volker ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Is the op amp just a unity gain buffer or does it have any gain setting resistors that might be adjusted? I'm just wondering if you could tailor the gain to reduce the swing rather than require the oscillator to effectively require a larger swing. The 344310-T is likely to have come from a Trimble Nortel NTGS50AA, that might even be the only source although I don't know for sure, and the EFC swing on those runs from 3 to 6 volts, or at least that's the hunt range, so the 344310-T needs to tune to 10MHz with an EFC somewhere within that range and that would have been a design or selection restraint on the oscillator when new. Older units are likely to be closer to the top of that range and I know some have exceeded 6 volts whilst still seeming to be otherwise ok, so it's probably a fair bet, with that oscillator for example, that you wouldn't need to drop below three volts anyway. Obviously other oscillators could have different requirements and the pot arrangement certainly makes it a bit more versatile, but well worth leaving that out if possible, and perhaps part of that moderate effort might be for others to characterise their oscillator first and then adjust a few values accordingly. Regards Nigel GM8PZR In a message dated 31/01/2014 20:19:51 GMT Standard Time, b...@evoria.net writes: I'm trying to put something together that is generic enough for the guys on the VE2ZAZ GPS Standard board, but that will be relatively free of temperature issues. Yeah, I know: an impossible task. The precision of the GPSDO is probably not in the same league as what this board is used to. The DAC is actually a 10-bit PWM with 4 bits of dither. The output from the board comes from an op-amp. The OCXO (for me) is a Trimble 34310-T. Its range across 0 to +5V is about 7.5Hz. I'm trying to reduce that to 2Hz. In spite of those limitations, it works well. I'm just trying to wring every last bit of performance out of it, but in a way that my results could be g enerally repeatable by someone who was willing to make a moderate effort. I didn't have any problem with finding 5PPM/C resistors for the 20K and 6.8k. The others were a different story. I found a 15PPM for the pot, and 5PPM and 10PPM for the others in values that should be close enough. I think I'll look around on Mouser a bit more before I press the buy button, but this is probably what I'll wind up getting. Bob From: gandal...@aol.com gandal...@aol.com To: time-nuts@febo.com Sent: Friday, January 31, 2014 1:18 PM Subject: Re: [time-nuts] EFC divider resistors It's hard to be sure without knowing the characteristics of the DAC ouput and the oscillator EFC, but if you're only making a one off I wonder if it might perhaps be possible to simplify that arrangement to just a potential divider using selected values and being fed from the DAC and tapped off into the EFC? Regards Nigel GM8PZR In a message dated 31/01/2014 18:04:39 GMT Standard Time, b...@evoria.net writes: I just realized that I have a pot in the mix. I see one on Mouser with 25PPM/C, so I suppose I'll try that. Here's the circuit I'll use with the replacements. What I have in there now has the values of R3, R4, and R5 multiplied by 10 and R2 is 3.9K. I suppose it won't matter so much for the pot. http://www.evoria.net/AE6RV/GPSstd_PLL/EFC%20Divider/EFC2.png Bob From: Robert LaJeunesse rlajeune...@sbcglobal.net To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 11:40 AM Subject: Re: [time-nuts] EFC divider resistors Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse From: Bob Stewart b...@evoria.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 12:01 PM Subject: [time-nuts] EFC divider resistors I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth
Re: [time-nuts] EFC divider resistors
As to what the specs are on this oscillator, I couldn't say. I have two of them. The one in my GPSDO wants about 2.101V for 10MHz. The other one wants about 2.6V (from memory). So that pretty much limits my options to a divider and a summing device to bring the EFC back up for the oscillator. And, that's my preference, in any case. What I put together works just fine, except for during heating and cooling cycles in the house. In fact, when the unit was down on the work bench, it was working really well. I put it on top of the stack last night before I went to bed to see what would happen. It was ugly, as the HVAC vent is pretty close. Maybe I should make up some longer jumpers and put it on the floor to see how much that stabilizes it. Bob From: gandal...@aol.com gandal...@aol.com To: time-nuts@febo.com Sent: Friday, January 31, 2014 3:18 PM Subject: Re: [time-nuts] EFC divider resistors Is the op amp just a unity gain buffer or does it have any gain setting resistors that might be adjusted? I'm just wondering if you could tailor the gain to reduce the swing rather than require the oscillator to effectively require a larger swing. The 344310-T is likely to have come from a Trimble Nortel NTGS50AA, that might even be the only source although I don't know for sure, and the EFC swing on those runs from 3 to 6 volts, or at least that's the hunt range, so the 344310-T needs to tune to 10MHz with an EFC somewhere within that range and that would have been a design or selection restraint on the oscillator when new. Older units are likely to be closer to the top of that range and I know some have exceeded 6 volts whilst still seeming to be otherwise ok, so it's probably a fair bet, with that oscillator for example, that you wouldn't need to drop below three volts anyway. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Hi If you are going to attenuate the EFC *and* center it up around 3V you will also need a voltage reference. Even a good one has a TC. You also have oven current running in the ground pin which contributes to voltage issues (oven and EFC share a common ground). Past that, you have thermocouple issues (resistors, wires, OCXO pins are different materials) …. Bob On Jan 31, 2014, at 4:18 PM, gandal...@aol.com wrote: Is the op amp just a unity gain buffer or does it have any gain setting resistors that might be adjusted? I'm just wondering if you could tailor the gain to reduce the swing rather than require the oscillator to effectively require a larger swing. The 344310-T is likely to have come from a Trimble Nortel NTGS50AA, that might even be the only source although I don't know for sure, and the EFC swing on those runs from 3 to 6 volts, or at least that's the hunt range, so the 344310-T needs to tune to 10MHz with an EFC somewhere within that range and that would have been a design or selection restraint on the oscillator when new. Older units are likely to be closer to the top of that range and I know some have exceeded 6 volts whilst still seeming to be otherwise ok, so it's probably a fair bet, with that oscillator for example, that you wouldn't need to drop below three volts anyway. Obviously other oscillators could have different requirements and the pot arrangement certainly makes it a bit more versatile, but well worth leaving that out if possible, and perhaps part of that moderate effort might be for others to characterise their oscillator first and then adjust a few values accordingly. Regards Nigel GM8PZR In a message dated 31/01/2014 20:19:51 GMT Standard Time, b...@evoria.net writes: I'm trying to put something together that is generic enough for the guys on the VE2ZAZ GPS Standard board, but that will be relatively free of temperature issues. Yeah, I know: an impossible task. The precision of the GPSDO is probably not in the same league as what this board is used to. The DAC is actually a 10-bit PWM with 4 bits of dither. The output from the board comes from an op-amp. The OCXO (for me) is a Trimble 34310-T. Its range across 0 to +5V is about 7.5Hz. I'm trying to reduce that to 2Hz. In spite of those limitations, it works well. I'm just trying to wring every last bit of performance out of it, but in a way that my results could be g enerally repeatable by someone who was willing to make a moderate effort. I didn't have any problem with finding 5PPM/C resistors for the 20K and 6.8k. The others were a different story. I found a 15PPM for the pot, and 5PPM and 10PPM for the others in values that should be close enough. I think I'll look around on Mouser a bit more before I press the buy button, but this is probably what I'll wind up getting. Bob From: gandal...@aol.com gandal...@aol.com To: time-nuts@febo.com Sent: Friday, January 31, 2014 1:18 PM Subject: Re: [time-nuts] EFC divider resistors It's hard to be sure without knowing the characteristics of the DAC ouput and the oscillator EFC, but if you're only making a one off I wonder if it might perhaps be possible to simplify that arrangement to just a potential divider using selected values and being fed from the DAC and tapped off into the EFC? Regards Nigel GM8PZR In a message dated 31/01/2014 18:04:39 GMT Standard Time, b...@evoria.net writes: I just realized that I have a pot in the mix. I see one on Mouser with 25PPM/C, so I suppose I'll try that. Here's the circuit I'll use with the replacements. What I have in there now has the values of R3, R4, and R5 multiplied by 10 and R2 is 3.9K. I suppose it won't matter so much for the pot. http://www.evoria.net/AE6RV/GPSstd_PLL/EFC%20Divider/EFC2.png Bob From: Robert LaJeunesse rlajeune...@sbcglobal.net To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 11:40 AM Subject: Re: [time-nuts] EFC divider resistors Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos
Re: [time-nuts] EFC divider resistors
Hi Bob, Do you think that maybe the oven current difference when the temperature changes could be at the root of this? To me, it seems like this started when I put the divider in. Before that, drift might have been hidden due to the lower resolution, I suppose. In any case, Mouser has my money now, and we'll see what happens when better quality resistors are put in. BTW, I'm feeding the pull-up divider with +5V from a 7805C bolted to the case. I could switch that to the +6V VRef from the OCXO if you think that would make any difference. The case used to be an HP 37203A. From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 3:50 PM Subject: Re: [time-nuts] EFC divider resistors Hi If you are going to attenuate the EFC *and* center it up around 3V you will also need a voltage reference. Even a good one has a TC. You also have oven current running in the ground pin which contributes to voltage issues (oven and EFC share a common ground). Past that, you have thermocouple issues (resistors, wires, OCXO pins are different materials) …. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
What is your cost goal? Bert Kehren In a message dated 1/31/2014 3:19:50 P.M. Eastern Standard Time, b...@evoria.net writes: I'm trying to put something together that is generic enough for the guys on the VE2ZAZ GPS Standard board, but that will be relatively free of temperature issues. Yeah, I know: an impossible task. The precision of the GPSDO is probably not in the same league as what this board is used to. The DAC is actually a 10-bit PWM with 4 bits of dither. The output from the board comes from an op-amp. The OCXO (for me) is a Trimble 34310-T. Its range across 0 to +5V is about 7.5Hz. I'm trying to reduce that to 2Hz. In spite of those limitations, it works well. I'm just trying to wring every last bit of performance out of it, but in a way that my results could be generally repeatable by someone who was willing to make a moderate effort. I didn't have any problem with finding 5PPM/C resistors for the 20K and 6.8k. The others were a different story. I found a 15PPM for the pot, and 5PPM and 10PPM for the others in values that should be close enough. I think I'll look around on Mouser a bit more before I press the buy button, but this is probably what I'll wind up getting. Bob From: gandal...@aol.com gandal...@aol.com To: time-nuts@febo.com Sent: Friday, January 31, 2014 1:18 PM Subject: Re: [time-nuts] EFC divider resistors It's hard to be sure without knowing the characteristics of the DAC ouput and the oscillator EFC, but if you're only making a one off I wonder if it might perhaps be possible to simplify that arrangement to just a potential divider using selected values and being fed from the DAC and tapped off into the EFC? Regards Nigel GM8PZR In a message dated 31/01/2014 18:04:39 GMT Standard Time, b...@evoria.net writes: I just realized that I have a pot in the mix. I see one on Mouser with 25PPM/C, so I suppose I'll try that. Here's the circuit I'll use with the replacements. What I have in there now has the values of R3, R4, and R5 multiplied by 10 and R2 is 3.9K. I suppose it won't matter so much for the pot. http://www.evoria.net/AE6RV/GPSstd_PLL/EFC%20Divider/EFC2.png Bob From: Robert LaJeunesse rlajeune...@sbcglobal.net To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 11:40 AM Subject: Re: [time-nuts] EFC divider resistors Jellybean resistors can have a tempco in the 100s of PPM per degree C. Some precision resistors are as low as 25 PPM/C while really good resistors can be had at 5 PPM/C. Better yet look for a resistor array where part tracking is called out. Some arrays get below 5 PPM tracking so the division ratio holds much better than the absolute value. (I find the DigiKey part search tool helpful in finding the low PPM parts I want.) Another possibility is an integrated resistive divider like the Maxim MAX549x series. The have pre-trimmed dividers in a number of ratios and values, typically with 35 PPM/C absolute tempcos but ratiotempcos as low as 2 PPM/C. Bob LaJeunesse From: Bob Stewart b...@evoria.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 12:01 PM Subject: [time-nuts] EFC divider resistors I put a divider network in the EFC line of my GPSDO to restrict the OCXO range to 2Hz. Now I'm seeing heat-related drift that wasn't apparent before. I put a 20K resistor from the same strip on my 3456A, and the warmth of holding it between fingers moves it by about 50 ohms. What type of resistors should I put in there? Or am I chasing a problem that doesn't exist? Totally out of my league here. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Around $25.00 to reproduce the final result. The cost goal for me to make it work is considerably more elastic. It's a project that I'm having fun with. There is no commercial market. From: ewkeh...@aol.com ewkeh...@aol.com To: time-nuts@febo.com Sent: Friday, January 31, 2014 4:25 PM Subject: Re: [time-nuts] EFC divider resistors What is your cost goal? Bert Kehren ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Don't underestimate the effect of resistors being at different temperatures. The tempco isn't linear at all, so your drift caused by ambient temp won't be the same at the different resistors. It is best to have them at the same value! I'd been experimenting quite some days to find a reasonable solution with single resistors. It's essential to have them at the same temperature and to couple them thermally as good as you can. Precision resistor dividers do it just the same way: very small resistor pills very tightly placed on a very good thermally conducting substrate. If you find the right value/ratio, and are game for paying about 30$ you can get a ready-to-use divider from Vishay or so. Another suggestion: replace the divider R3/4/5 by a precision reference at the desired voltage. 5V sounds like a TTL supply - that would be no good idea. My personal story: When I had my divider placed on the PCB I was wondering the oscilloscope showing sudden milli volt jumps from time to time (where I expected a noise of some micro volts...). After hours of searching I noticed a correlation with the wind blowing outside my shack. It was a small crack in the window that let a tiny airstream flow across my PCB, so tiny, I couldn't sense. Volker Am 31.01.2014 21:23, schrieb Bob Stewart: Hi Volker, Thanks for the ideas. The resistors are all within a short radius of each other. I hadn't thought about bundling them all together. I suppose I could epoxy them together as a last resort. I've got some EPF foam, so I could try putting that on the board right against them. In fact, I could try that while waiting for the new parts. I've already used foam to fill most of the space in the box, except for around and above the OCXO. From: Volker Esper ail...@t-online.de To: Robert LaJeunesse lajeune...@mail.com; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 1:51 PM Subject: Re: [time-nuts] EFC divider resistors Sorry, missing picture... Am 31.01.2014 20:47, schrieb Volker Esper: Here's how to place the divider resistors. The picture is from 1992, I didn't use SMDs then. But the results are promising at a very low price. Isolierband = insulation tape wärmeleit. Kern = thermoconducting core The picture shows two examples, the left one if you need three resistors, the right one if you need six. Use metal film types with low tempco. Keep in mind: it's the fluctuating _difference_ between the resistor values, that'll kill your stability. So avoid everything, that leads to different temperatures at the resistors. In particular avoid placing them into an airstream. Volker ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Hi A 7805 has a *rated* temperature coefficient of 2 mv / C. Most parts do way better than this. The problem is knowing if you have a good part or not. On a 5V part, your reference could be running 400 ppm/C. Since the divider has no impact on this number, it over-rides what ever you do with the divider resistors. A good voltage reference will set you back about $50 or so. You commonly see a couple of mv of variation in the ground pin voltage with oven current depending on exactly where the pin is terminated. Any change in the ground setup can be an issue on an OCXO with the EFC in common with the oven (which is most parts). Bob On Jan 31, 2014, at 5:01 PM, Bob Stewart b...@evoria.net wrote: Hi Bob, Do you think that maybe the oven current difference when the temperature changes could be at the root of this? To me, it seems like this started when I put the divider in. Before that, drift might have been hidden due to the lower resolution, I suppose. In any case, Mouser has my money now, and we'll see what happens when better quality resistors are put in. BTW, I'm feeding the pull-up divider with +5V from a 7805C bolted to the case. I could switch that to the +6V VRef from the OCXO if you think that would make any difference. The case used to be an HP 37203A. From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 3:50 PM Subject: Re: [time-nuts] EFC divider resistors Hi If you are going to attenuate the EFC *and* center it up around 3V you will also need a voltage reference. Even a good one has a TC. You also have oven current running in the ground pin which contributes to voltage issues (oven and EFC share a common ground). Past that, you have thermocouple issues (resistors, wires, OCXO pins are different materials) …. Bob ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Any idea what the usual temperature coefficient is for the VRef output of the OCXO? I looked under the Trimble label of my spare and found: DOC2127 and 44/1416. The one I have installed is probably the same. From: Bob Camp li...@rtty.us To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 6:17 PM Subject: Re: [time-nuts] EFC divider resistors Hi A 7805 has a *rated* temperature coefficient of 2 mv / C. Most parts do way better than this. The problem is knowing if you have a good part or not. On a 5V part, your reference could be running 400 ppm/C. Since the divider has no impact on this number, it over-rides what ever you do with the divider resistors. A good voltage reference will set you back about $50 or so. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Must be military prices. If using 5 PPM resistors in the build a reference much better than that isn't needed, especially if the temperature is somewhat controlled, like time nuts do. A commercial 3 PPM/C part, the LM4140A, is $4.54 each in singles. At 2.2uV p-p it's reasonably quiet as well. Considering stability influences, what provides the DAC reference? That's rather important as well. Bob LaJeunesse I'd also note the 2 PPM ratio tracking dividers, the MAX549x series, can be had in the $3.49 range, also not all that expensive. From: Bob Camp li...@rtty.us To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 7:17 PM Subject: Re: [time-nuts] EFC divider resistors ... A good voltage reference will set you back about $50 or so. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Hi If you attenuate the DAC 100:1 to 1000:1 before it hits the OCXO, the DAC does not matter much. That may sound like a crazy ratio, but it is indeed possible with some of these OCXO EFC ranges. They can have a *lot* of swing. The reference is an LTZ1000, they run about $50 in single piece lots. You can get resistors that run below 1 ppm tracking without a whole lot of effort Bob On Jan 31, 2014, at 8:38 PM, Robert LaJeunesse rlajeune...@sbcglobal.net wrote: Must be military prices. If using 5 PPM resistors in the build a reference much better than that isn't needed, especially if the temperature is somewhat controlled, like time nuts do. A commercial 3 PPM/C part, the LM4140A, is $4.54 each in singles. At 2.2uV p-p it's reasonably quiet as well. Considering stability influences, what provides the DAC reference? That's rather important as well. Bob LaJeunesse I'd also note the 2 PPM ratio tracking dividers, the MAX549x series, can be had in the $3.49 range, also not all that expensive. From: Bob Camp li...@rtty.us To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 7:17 PM Subject: Re: [time-nuts] EFC divider resistors ... A good voltage reference will set you back about $50 or so. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
I am not sure if anyone else mentioned this, Placing the parts against the oscillator with a little thermal epoxy under a small piece of foam so they are at least partially ovenized should really help. Thomas Knox From: li...@rtty.us Date: Fri, 31 Jan 2014 22:36:46 -0500 To: lajeune...@mail.com; time-nuts@febo.com Subject: Re: [time-nuts] EFC divider resistors Hi If you attenuate the DAC 100:1 to 1000:1 before it hits the OCXO, the DAC does not matter much. That may sound like a crazy ratio, but it is indeed possible with some of these OCXO EFC ranges. They can have a *lot* of swing. The reference is an LTZ1000, they run about $50 in single piece lots. You can get resistors that run below 1 ppm tracking without a whole lot of effort Bob On Jan 31, 2014, at 8:38 PM, Robert LaJeunesse rlajeune...@sbcglobal.net wrote: Must be military prices. If using 5 PPM resistors in the build a reference much better than that isn't needed, especially if the temperature is somewhat controlled, like time nuts do. A commercial 3 PPM/C part, the LM4140A, is $4.54 each in singles. At 2.2uV p-p it's reasonably quiet as well. Considering stability influences, what provides the DAC reference? That's rather important as well. Bob LaJeunesse I'd also note the 2 PPM ratio tracking dividers, the MAX549x series, can be had in the $3.49 range, also not all that expensive. From: Bob Camp li...@rtty.us To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, January 31, 2014 7:17 PM Subject: Re: [time-nuts] EFC divider resistors ... A good voltage reference will set you back about $50 or so. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
li...@rtty.us said: A 7805 has a *rated* temperature coefficient of 2 mv / C. Most parts do way better than this. The problem is knowing if you have a good part or not. On a 5V part, your reference could be running 400 ppm/C. Since the divider has no impact on this number, it over-rides what ever you do with the divider resistors. A good voltage reference will set you back about $50 or so. Plan B would be to keep the 7805 at a constant temperature. You commonly see a couple of mv of variation in the ground pin voltage with oven current depending on exactly where the pin is terminated. Any change in the ground setup can be an issue on an OCXO with the EFC in common with the oven (which is most parts). Again, plan B would be to keep the OCXO at a constant temperature so the heater current is (close) to constant and the offset on the ground pin due to heater current would be constant. - I've heard comments about offset due to a single ground pin for several/many years, so it's nothing new. Why are manufacturers not providing separate pins? Are there OCXOs (that I haven't noticed) with 2 ground pins? Is the problem backward compatibility? In that case, I'd expect there would be a pinout with a new second-ground pin that offered an interesting beat-this challenge to other vendors. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] EFC divider resistors
Hi Tom, Actually, no-one has. And come to think of it, maybe that's the root of the problem. I have the resistors lying on their sides right under the OCXO on the opposite side (bottom) of the PC board. Any air circulation is going to make them weave and wobble a bit in value. I'll have to see if there's anything I can do about it quickly with a piece of foam. I'll for sure do something when the new parts come in. I may have to cut a hole in the PCB the OCXO is mounted on. thanks! Bob From: Tom Knox act...@hotmail.com To: Time-Nuts time-nuts@febo.com Sent: Friday, January 31, 2014 9:54 PM Subject: Re: [time-nuts] EFC divider resistors I am not sure if anyone else mentioned this, Placing the parts against the oscillator with a little thermal epoxy under a small piece of foam so they are at least partially ovenized should really help. Thomas Knox ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
