Re: [time-nuts] Why a 10MHz sinewave output?
Actually, I do have an earth available for calibration to my lab. It's just outside the window. During the day I can take sun sightings, and during the night star sightings (barring cloudy weather). I cannot measure the length of a second as accurately as other lab equipment can, but the expensive equipment in my lab that measures the second accurately cannot tell me time-of-day or day of year. (with the exception of a WWV or GPS receiver). Craig McCartney 160 Montalvo Road Palomar Park, CA 94062 -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson Sent: Wednesday, February 08, 2012 4:51 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Why a 10MHz sinewave output? On 02/08/2012 03:25 PM, Craig S McCartney wrote: We already have one of those that everybody can use. It's called the earth. Yes, but you don't have it hanging in a neat position in your office, living room or lab, now do you? Besides, if you are a time-nut your rock will be more time-accurate than the real thing. :) I haven't special ordered a backup earth for my lab, or at least I won't admit to it, as you all know that I have at least three operational and a few stand-bys to put into operation in case I need to service one of them. Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
Hal Murray wrote: li...@rtty.us said: Thank goodness for that inertia. I can still cable up a 100Kcps sine wave standard to run stuff from long ago. When I run into a box that uses a T1 signal for a clock reference - not so easy in the basement. How much gear is there that uses T1 for a clock input? Is there any interest in a board/chip/whatever that converts 10 MHz to T1? A clean design using a decimal DDS should fit into a small FPGA, maybe a CPLD. There is quite a bit of telecom gear that will take a T1(or E1) as a clock reference. A T1 BITS will provide an all 1's AMI signal which looks like 772 kHz on a scope. ___ 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] Why a 10MHz sinewave output?
We already have one of those that everybody can use. It's called the earth. Craig McCartney 160 Montalvo Road Palomar Park, CA 94062 -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson Sent: Tuesday, February 07, 2012 12:41 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Why a 10MHz sinewave output? On 02/07/2012 09:02 AM, David J Taylor wrote: For the real analog fans, how about a 1 Hz sinewave output and watch for the zero-crossings! G Precise? No! 11 uHz sine anyone, 24 hours period? Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
Hi Some (but by no means all) gear actually looks at some of the data fields on the T1 before it will accept it as a reference. In most cases a bits clock does fine. Of course you do need a proper balanced line driver and all that stuff to get it running. Still not something that's readily available in my basement. At work - not a problem. The simple / stupid way to do it is to use a framer chip. They are cheap these days and they have all the driver stuff built in. They will even pack the data fields with hey, I'm a good clock - use me. Run a cheap PLL to generate the framer clock and you are up and running. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of J.D. Schoedel Sent: Wednesday, February 08, 2012 1:52 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Why a 10MHz sinewave output? Hal Murray wrote: li...@rtty.us said: Thank goodness for that inertia. I can still cable up a 100Kcps sine wave standard to run stuff from long ago. When I run into a box that uses a T1 signal for a clock reference - not so easy in the basement. How much gear is there that uses T1 for a clock input? Is there any interest in a board/chip/whatever that converts 10 MHz to T1? A clean design using a decimal DDS should fit into a small FPGA, maybe a CPLD. There is quite a bit of telecom gear that will take a T1(or E1) as a clock reference. A T1 BITS will provide an all 1's AMI signal which looks like 772 kHz on a scope. ___ 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] Why a 10MHz sinewave output?
Hey, you're not supposed to actually read those planning applications for hyperspace bypasses! D. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Mark Sims Sent: 08 February 2012 16:54 To: time-nuts@febo.com Subject: [time-nuts] Why a 10MHz sinewave output? It's slated for destruction around December 21 of this year... We already have one of those that everybody can use. It's called the earth. ___ 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] Why a 10MHz sinewave output?
On 02/08/2012 06:15 PM, Bob Camp wrote: Hi Some (but by no means all) gear actually looks at some of the data fields on the T1 before it will accept it as a reference. In most cases a bits clock does fine. Of course you do need a proper balanced line driver and all that stuff to get it running. Still not something that's readily available in my basement. At work - not a problem. The simple / stupid way to do it is to use a framer chip. They are cheap these days and they have all the driver stuff built in. They will even pack the data fields with hey, I'm a good clock - use me. Run a cheap PLL to generate the framer clock and you are up and running. The T1/DS1 signal as well as the E1 signal has a way to indicate to which standard level the delivered clock is traceable to. If you are in luck, you get a PRS (ANSI top reference) or PRC (ETSI/ITU top reference) indication, which would mean that you have a G.811 compatible clock within 1E-11 in frequency. In their infinite wisdom the 1544 kHz and 2048 kHz standards slightly out of tune with each other as they stem from different advances in the respective PDH hierarchy development, which later rippled into the SONET and SDH counter-parts. Their SSM codes for Quality Level encoding has now rippled over to Synchronous Ethernet, which is nothing but a very strange SDH interface rate. The ITU-T G.781 standard is a place to get lost to understand these messages, so is ANSI T1.101. Digging around the ITU-T G.810-813 and G.823-825 specs is recommended. There is also several good ETSI specs and a good TR to read up on. Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
On 2/8/12 4:51 PM, Magnus Danielson wrote: On 02/08/2012 03:25 PM, Craig S McCartney wrote: We already have one of those that everybody can use. It's called the earth. Yes, but you don't have it hanging in a neat position in your office, living room or lab, now do you? Besides, if you are a time-nut your rock will be more time-accurate than the real thing. :) I haven't special ordered a backup earth for my lab, or at least I won't admit to it, as you all know that I have at least three operational and a few stand-bys to put into operation in case I need to service one of them. And now you know why we keep sending those spacecraft with high performance radios to Mars. Because, you know, with all those earthquakes and tsunamis, the Earth rotation keeps changing. And that enormously massive moon also interacts with the rotation too, not to mention our thick atmosphere. Mars, tiny moons, almost no atmosphere, no oceans, seismically quiet... I'll pitch it as a new slogan: Mars clocks, when Earth rotation just isn't stable enough. ___ 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] Why a 10MHz sinewave output?
I thought the same thing but I think Mark was referring to the end date of the Mayan calender. Now those guys were Time-Nuts!! Ed On 2/8/2012 12:09 PM, David C. Partridge wrote: Hey, you're not supposed to actually read those planning applications for hyperspace bypasses! D. -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Mark Sims Sent: 08 February 2012 16:54 To: time-nuts@febo.com Subject: [time-nuts] Why a 10MHz sinewave output? It's slated for destruction around December 21 of this year... We already have one of those that everybody can use. It's called the earth. ___ 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] Why a 10MHz sinewave output?
For the real analog fans, how about a 1 Hz sinewave output and watch for the zero-crossings! G Precise? No! David -- SatSignal software - quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] Why a 10MHz sinewave output?
On 02/07/2012 02:16 AM, Bob Camp wrote: Hi When the customers started asking in the 1930's, generating a square wave at high frequency was not so easy…. Which is my point, the power of tradition can sometimes be stronger than logical reasoning for the application needs. Today many of the oscillators can be had in one or more of CMOS/Clipped-Sine/Sine outputs. Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
On 02/07/2012 05:58 AM, Hal Murray wrote: mag...@rubidium.dyndns.org said: Oh... nothing really beats it's what customers traditionally asks for Squarewave out provides high slew-rate which reduces the effect of additional noise. Right. But if you have a single frequency you can easily filter out most of the noise. --- As clock speed has increased over the years, a new field has emerged. A good name is signal integrity. That covers clock distribution, data distribution, and power supply bypassing/regulation/decoupling. It's basically all the analog stuff needed to make digital logic work in the real world. The technology for distributing more bits is also useful for reducing noise/jitter. There are whole families of chips for clock distribution. Many include PLLs which can correct for trace length, make other frequencies, and/or do the spread spectrum thing to reduce EMI. The ones I'm familiar with are targeted at digital applications. Jitter within a small fraction of a bit cell is fine. The target market doesn't care about time-nut class super clean clocks. There are other families of chips (or parts of big chips) for driving/receiving clocks and data between boards/boxes. Most of those are now differential so I assume twisted pair is cheaper than coax. SATA between your motherboard and hard disk is a good example. It runs at 1.5, 3, or 6 gigabits/second. Wiki says up to 1 meter. If you want a good example of the technology in this area, check out gigabit ethernet over CAT5. It's 5 level encoding (2 bits/baud) at 125 megabaud/sec over 4 pair in both directions over each pair. Twisting my pre and post emphasis and receiver equalizers on the multi-gigabit links... yes. An upswing for TDR/TDTs as well. Optical stuff is still single-ended. :) Well, you do not access the carriers directly as with electrical signals, but different polarity of signal still exists. There are some very low cost optical links for distribution of audio. The key idea is to use plastic rather than glass. Bandwidth is limited but cost is low. Oh, those horrid links creates a bundle of reflections and dispersion, causing a greater need of compensation, something which is never given as treatment. A multimode glass fibre would be a better choice, as the components are cheap now. Even single mode 1310 nm is fairly cheap now. Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
On 02/07/2012 09:02 AM, David J Taylor wrote: For the real analog fans, how about a 1 Hz sinewave output and watch for the zero-crossings! G Precise? No! 11 uHz sine anyone, 24 hours period? Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
Or 23h 56m 4.091s /tvb 11 uHz sine anyone, 24 hours period? Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
Hi Thank goodness for that inertia. I can still cable up a 100Kcps sine wave standard to run stuff from long ago. When I run into a box that uses a T1 signal for a clock reference - not so easy in the basement. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson Sent: Tuesday, February 07, 2012 3:33 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Why a 10MHz sinewave output? On 02/07/2012 02:16 AM, Bob Camp wrote: Hi When the customers started asking in the 1930's, generating a square wave at high frequency was not so easy.. Which is my point, the power of tradition can sometimes be stronger than logical reasoning for the application needs. Today many of the oscillators can be had in one or more of CMOS/Clipped-Sine/Sine outputs. Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
li...@rtty.us said: Thank goodness for that inertia. I can still cable up a 100Kcps sine wave standard to run stuff from long ago. When I run into a box that uses a T1 signal for a clock reference - not so easy in the basement. How much gear is there that uses T1 for a clock input? Is there any interest in a board/chip/whatever that converts 10 MHz to T1? A clean design using a decimal DDS should fit into a small FPGA, maybe a CPLD. -- These are my opinions, not necessarily my employer's. 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] Why a 10MHz sinewave output?
On 02/07/2012 08:12 PM, Hal Murray wrote: li...@rtty.us said: Thank goodness for that inertia. I can still cable up a 100Kcps sine wave standard to run stuff from long ago. When I run into a box that uses a T1 signal for a clock reference - not so easy in the basement. How much gear is there that uses T1 for a clock input? Is there any interest in a board/chip/whatever that converts 10 MHz to T1? A clean design using a decimal DDS should fit into a small FPGA, maybe a CPLD. 1,544 MHz is a bit funny, 193*8 kHz. On the other hand, a 1250 sample long sample-memory and then toss that through a DAC and the sine can then be smoothed. A 2,048 MHz (256*8 kHz) could do just the same. If you need a squarewave, then a sine to square converter will produce a fairly accurate transition time signal. Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
Related question: Assuming I'm using 10MHz sine wave. What's the best physical cable to use? Is there any good reason to use 50 ohm cable? What about 75 ohm? I looked at a schematic of my counter and it looks like the 10MHz signal hits some high impedance chip inside.RG6 seems like the way to go. It's double shieled and lots of cable TV parts could be used. On Tue, Feb 7, 2012 at 11:12 AM, Hal Murray hmur...@megapathdsl.net wrote: li...@rtty.us said: Thank goodness for that inertia. I can still cable up a 100Kcps sine wave standard to run stuff from long ago. When I run into a box that uses a T1 signal for a clock reference - not so easy in the basement. How much gear is there that uses T1 for a clock input? Is there any interest in a board/chip/whatever that converts 10 MHz to T1? A clean design using a decimal DDS should fit into a small FPGA, maybe a CPLD. -- These are my opinions, not necessarily my employer's. 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. -- Chris Albertson Redondo Beach, California ___ 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] Why a 10MHz sinewave output?
On Tue, 7 Feb 2012 12:19:11 -0800 Chris Albertson albertson.ch...@gmail.com wrote: Related question: Assuming I'm using 10MHz sine wave. What's the best physical cable to use? Is there any good reason to use 50 ohm cable? What about 75 ohm? I looked at a schematic of my counter and it looks like the 10MHz signal hits some high impedance chip inside.RG6 seems like the way to go. It's double shieled and lots of cable TV parts could be used. There is no particular advantage in one or the other, at least not for most applications. It's tradition that measurement and (most) RF gear uses 50R, while TV and radio uses 75R. (there was once a reason for this, but i don't know it). When it comes to low frequency stuff (ie everything below a couple 100MHz) i would stick with 50R cable and connectors. Cheap cables aren't too bad for lab stuff. Although for time-nutty needs you might want to choose the ones with better shielding. When you go to higher frequencies (especially above 1GHz) i'd rather use 75R sat cables + F connectors. These are available in good qualities at low price. What you should not do is mix different impedances, as this will result in energy reflected back to the source, which might or might not damage it. But you will definitly have increased jitter due to the reflections. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] Why a 10MHz sinewave output?
On Tue, 7 Feb 2012 21:59:18 +0100 Attila Kinali att...@kinali.ch wrote: Related question: Assuming I'm using 10MHz sine wave. What's the best physical cable to use? Is there any good reason to use 50 ohm cable? What about 75 ohm? I looked at a schematic of my counter and it looks like the 10MHz signal hits some high impedance chip inside.RG6 seems like the way to go. It's double shieled and lots of cable TV parts could be used. There is no particular advantage in one or the other, at least not for most applications. It's tradition that measurement and (most) RF gear uses 50R, while TV and radio uses 75R. (there was once a reason for this, but i don't know it). Addendum: Your counter input is mostlikely 50R. Even if it just enters a chip, as the chip itself should be matched to 50R. The input impedance should be noted in the manual of the counter. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] Why a 10MHz sinewave output
On Tue, 07 Feb 2012 16:15:44 -0500 Mike Naruta AA8K a...@comcast.net wrote: On 02/07/2012 03:59 PM, Attila Kinali wrote: while TV and radio uses 75R. (there was once a reason for this, but i don't know it). A 4:1 balun takes old 300 ohm twinlead to 75 ohms. Thanks! This explains half it :-) Do you know why a 4:1 balun was used? And do you know why other RF stuff and lab equipment is 50R? Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] Why a 10MHz sinewave output
Try this for a history about the 50 OHM impedance: http://www.rfcafe.com/references/electrical/history-of-50-ohms.htm On Tue, Feb 7, 2012 at 10:30 PM, Attila Kinali att...@kinali.ch wrote: On Tue, 07 Feb 2012 16:15:44 -0500 Mike Naruta AA8K a...@comcast.net wrote: On 02/07/2012 03:59 PM, Attila Kinali wrote: while TV and radio uses 75R. (there was once a reason for this, but i don't know it). A 4:1 balun takes old 300 ohm twinlead to 75 ohms. Thanks! This explains half it :-) Do you know why a 4:1 balun was used? And do you know why other RF stuff and lab equipment is 50R? Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] Why a 10MHz sinewave output
On Tue, Feb 7, 2012 at 1:30 PM, Attila Kinali att...@kinali.ch wrote: On Tue, 07 Feb 2012 16:15:44 -0500 Mike Naruta AA8K a...@comcast.net wrote: On 02/07/2012 03:59 PM, Attila Kinali wrote: while TV and radio uses 75R. (there was once a reason for this, but i don't know it). A 4:1 balun takes old 300 ohm twinlead to 75 ohms. The required balun would need a 4:1 _impedence_ ratio. The square root of four would be the required turns ratio. So it is a 2:1 balun that you need. It's an easy integer number. If you want you balun to have an integer turns ratio like 1:1, 2:1, 3:1 and so on then the impedence rations are going to be 1:1, 4:1 or 9:1. which means you'd need coax to be either 300, 75 or 33 ohm. Those are the only choises you have if you start with 300 ohm and restrict your balun to have a simple integer turns ratio. A balun that matches 300 to 50 cable would have a 5:2 turns ratio but 5:2 is not exact. You can't to 300 -- 50 exactly. 49:20 is very close but there is not exact turns ratio that works Thanks! This explains half it :-) Do you know why a 4:1 balun was used? And do you know why other RF stuff and lab equipment is 50R? Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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. -- Chris Albertson Redondo Beach, California ___ 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] Why a 10MHz sinewave output?
50 ohms is a compromise between maximum power transfer and minimum attenuation, as mentioned in page 9 of Network Analyzer Basics (http://cp.literature.agilent.com/litweb/pdf/5965-7917E.pdf) Regards, Roberto EB4EQA -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Attila Kinali Sent: martes, 07 de febrero de 2012 21:59 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Why a 10MHz sinewave output? On Tue, 7 Feb 2012 12:19:11 -0800 Chris Albertson albertson.ch...@gmail.com wrote: Related question: Assuming I'm using 10MHz sine wave. What's the best physical cable to use? Is there any good reason to use 50 ohm cable? What about 75 ohm? I looked at a schematic of my counter and it looks like the 10MHz signal hits some high impedance chip inside.RG6 seems like the way to go. It's double shieled and lots of cable TV parts could be used. There is no particular advantage in one or the other, at least not for most applications. It's tradition that measurement and (most) RF gear uses 50R, while TV and radio uses 75R. (there was once a reason for this, but i don't know it). When it comes to low frequency stuff (ie everything below a couple 100MHz) i would stick with 50R cable and connectors. Cheap cables aren't too bad for lab stuff. Although for time-nutty needs you might want to choose the ones with better shielding. When you go to higher frequencies (especially above 1GHz) i'd rather use 75R sat cables + F connectors. These are available in good qualities at low price. What you should not do is mix different impedances, as this will result in energy reflected back to the source, which might or might not damage it. But you will definitly have increased jitter due to the reflections. Attila Kinali -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] Why a 10MHz sinewave output
On 2/7/2012 4:30 PM, Attila Kinali wrote: On Tue, 07 Feb 2012 16:15:44 -0500 Mike Naruta AA8Ka...@comcast.net wrote: On 02/07/2012 03:59 PM, Attila Kinali wrote: while TV and radio uses 75R. (there was once a reason for this, but i don't know it). A 4:1 balun takes old 300 ohm twinlead to 75 ohms. Thanks! This explains half it :-) Do you know why a 4:1 balun was used? And do you know why other RF stuff and lab equipment is 50R? In coax cables, it turns out that about 30 ohm impedance offers the greatest power handling capacity for a given diameter, and 70 ohms is nearly optimum for minimum loss. 50 ohms was a compromise for both factors, and IIRC had some other desirable physical characteristics. Twin-lead cable is in theory balanced (neither conductor grounded) while coax is unbalanced (shield is grounded). The balun is a balanced to unbalanced converter, and can also be designed to transform impedances, so a 4:1 ratio matches 300 to 75 ohm line. John ___ 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] Why a 10MHz sinewave output?
Hi As long as you are running a sine wave, and you don't change cables, you can run just about anything. The phase errors / reflections will work themselves out. 50 ohm plastic dielectric cable turns out to be the best for power handling at reasonable loss. 75 ohm cable turns out to be the best for loss per mile. Telcom and TV people went with 75 ohms. People who ran transmitters went with 50 ohms. If you change the dielectric, you can get best cases at somewhat different impedances. 50 ohm cable works best / easiest with 50 ohm connectors. Mixing 75 ohm connectors and 50 ohm connectors is not a good idea. The inner conductors on the connector are often different diameters and you tend to break one side or the other. Given the cost of (cheap) RG-58 or RG-59, I don't see a big advantage to switching impedance to save money at 10 MHz. Down there the skin depth is what will impact your shield the most. The fancy extra aluminum foil layers don't have much thickness. Of course if you go to hard line then it's a whole different story... Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Chris Albertson Sent: Tuesday, February 07, 2012 3:19 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Why a 10MHz sinewave output? Related question: Assuming I'm using 10MHz sine wave. What's the best physical cable to use? Is there any good reason to use 50 ohm cable? What about 75 ohm? I looked at a schematic of my counter and it looks like the 10MHz signal hits some high impedance chip inside.RG6 seems like the way to go. It's double shieled and lots of cable TV parts could be used. On Tue, Feb 7, 2012 at 11:12 AM, Hal Murray hmur...@megapathdsl.net wrote: li...@rtty.us said: Thank goodness for that inertia. I can still cable up a 100Kcps sine wave standard to run stuff from long ago. When I run into a box that uses a T1 signal for a clock reference - not so easy in the basement. How much gear is there that uses T1 for a clock input? Is there any interest in a board/chip/whatever that converts 10 MHz to T1? A clean design using a decimal DDS should fit into a small FPGA, maybe a CPLD. -- These are my opinions, not necessarily my employer's. 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. -- Chris Albertson Redondo Beach, California ___ 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] Why a 10MHz sinewave output?
On Tue, Feb 7, 2012 at 1:03 PM, Attila Kinali att...@kinali.ch wrote: Addendum: Your counter input is mostlikely 50R. Even if it just enters a chip, as the chip itself should be matched to 50R. The input impedance should be noted in the manual of the counter. The counter specs say that any 2.5 volt or greater sine or TTL level square wave signal is acceptable. I think they use a 74LS14 chip or something like that. This counter was made in the 1980s, not quite current tech. Chris Albertson Redondo Beach, California ___ 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] Why a 10MHz sinewave output
On 2/7/12 1:30 PM, Attila Kinali wrote: On Tue, 07 Feb 2012 16:15:44 -0500 Mike Naruta AA8Ka...@comcast.net wrote: On 02/07/2012 03:59 PM, Attila Kinali wrote: while TV and radio uses 75R. (there was once a reason for this, but i don't know it). A 4:1 balun takes old 300 ohm twinlead to 75 ohms. Thanks! This explains half it :-) Do you know why a 4:1 balun was used? A dipole has a feed point impedance of about 65-75 ohms. A folded dipole has an impedance of 4 times that, so 300 ohm twinlead was a nice match. 75ohms is, in general, the lowest loss impedance for a given dielectric (based on the ratio of inner and outer diameters and skin depth, etc.) 30 some odd ohms is the highest power handling impedance (lowest peak E-field) And do you know why other RF stuff and lab equipment is 50R? Compromise of one sort or another. http://www.microwaves101.com has a nice discussion of this.. ___ 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] Why a 10MHz sinewave output?
Hi Modern gear often has high input standard plugs. People tend to daisy chain gear with T connectors. That makes for issues if they are all low impedance. Bob On Feb 7, 2012, at 5:31 PM, Chris Albertson albertson.ch...@gmail.com wrote: On Tue, Feb 7, 2012 at 1:03 PM, Attila Kinali att...@kinali.ch wrote: Addendum: Your counter input is mostlikely 50R. Even if it just enters a chip, as the chip itself should be matched to 50R. The input impedance should be noted in the manual of the counter. The counter specs say that any 2.5 volt or greater sine or TTL level square wave signal is acceptable. I think they use a 74LS14 chip or something like that. This counter was made in the 1980s, not quite current tech. Chris Albertson Redondo Beach, California ___ 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] Why a 10MHz sinewave output
Azelio Boriani wrote: Try this for a history about the 50 OHM impedance: http://www.rfcafe.com/references/electrical/history-of-50-ohms.htm The reference is full of errors. The lowest loss in coax occurs when the ratio of the diameters is 3.6 to 1, regardless of dielectric. For air dielectric, this works out to 76.7 ohms. For polyethylene, it works out to just over 50 ohms if you assume a dielectric constant of 2.3. It is also worth noting that the difference in loss between 3.6 to 1 and 2.3 to 1 is very slight and not worth worrying about in most practical cases. What is probably more important is that higher impedance cable uses much less copper in the center conductor for the same loss. The story about 2 inch and 3/4 inch pipe might be true. The thinnest copper tubing, type M, has an ID for trade size 2 inch of 2.009 inches and and OD for trade size 3/4 inch of 0.875 inch, which is very close to 2.3 to 1. Of course there is also type K and type L and lots of other sizes, so this story may be a case of data mining (IE you can always find some combination of pipes to support any ratio you claim). Rick N6RK ___ 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] Why a 10MHz sinewave output?
A 10Mhz to T1 clock generator would be a cool project but in the event I were to need a standalone T1 clock source at home I'd probably just grab a CSU / DSU from ebay (or ask one of my former employers if they would let me acquire one from their junk pile) that could serve as clock generator. One day I suspect I'd eventually find a use for two such devices to set up a networked set of pbx's (each with it's own clock source) in my basement to prove to a former colleague of mine that you really can network pbx's together via T1's without one pbx being the master and the other a slave from a clocking perspective. This project will likely need to wait for my retirement. --- On Tue, 2/7/12, Hal Murray hmur...@megapathdsl.net wrote: From: Hal Murray hmur...@megapathdsl.net Subject: Re: [time-nuts] Why a 10MHz sinewave output? To: Discussion of precise time and frequency measurement time-nuts@febo.com Received: Tuesday, February 7, 2012, 2:12 PM li...@rtty.us said: Thank goodness for that inertia. I can still cable up a 100Kcps sine wave standard to run stuff from long ago. When I run into a box that uses a T1 signal for a clock reference - not so easy in the basement. How much gear is there that uses T1 for a clock input? Is there any interest in a board/chip/whatever that converts 10 MHz to T1? A clean design using a decimal DDS should fit into a small FPGA, maybe a CPLD. -- These are my opinions, not necessarily my employer's. 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.
Re: [time-nuts] Why a 10MHz sinewave output
I think the real relation is 50 ohm coax is just 75 ohm air line with polyethylene dielectric added. -Chuck Harris Rick Karlquist wrote: Azelio Boriani wrote: Try this for a history about the 50 OHM impedance: http://www.rfcafe.com/references/electrical/history-of-50-ohms.htm The reference is full of errors. The lowest loss in coax occurs when the ratio of the diameters is 3.6 to 1, regardless of dielectric. For air dielectric, this works out to 76.7 ohms. For polyethylene, it works out to just over 50 ohms if you assume a dielectric constant of 2.3. It is also worth noting that the difference in loss between 3.6 to 1 and 2.3 to 1 is very slight and not worth worrying about in most practical cases. What is probably more important is that higher impedance cable uses much less copper in the center conductor for the same loss. The story about 2 inch and 3/4 inch pipe might be true. The thinnest copper tubing, type M, has an ID for trade size 2 inch of 2.009 inches and and OD for trade size 3/4 inch of 0.875 inch, which is very close to 2.3 to 1. Of course there is also type K and type L and lots of other sizes, so this story may be a case of data mining (IE you can always find some combination of pipes to support any ratio you claim). Rick N6RK ___ 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] Why a 10MHz sinewave output?
On Sun, 05 Feb 2012 19:50:28 -0800 bob grant bobgr...@fastmail.fm wrote: Why is 10MHz output of many sources or distribution amps in the form of a sinewave? Is it something to do with signal reflections or ease of isolation? Since zero crossing detectors are susceptible to noise wouldn't a fast TTL square wave be more appropriate for signal distribution within a equipment rack? The advantage of a sine wave is that you have a single, bounded frequency. A square wave has quite strong components at odd multiples of the base frequency, theoretically going up to infinity. To get a good shape of the signal you need at least the first three of the harmonics, resulting in a seven times increased bandwidth need. Beside of the more complicated handling of the higher frequency components, you also have to think about dispersion of the signal if you go trough filters or use longer cables. Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Why a 10MHz sinewave output?
Indeed the long cable runs are tough. Though today we have differential cable drivers that do quite well to the Ghz range. But certainly back in the dark ages the sine wave was a very reasonable way to go. Regards Paul On Mon, Feb 6, 2012 at 3:56 AM, Attila Kinali att...@kinali.ch wrote: On Sun, 05 Feb 2012 19:50:28 -0800 bob grant bobgr...@fastmail.fm wrote: Why is 10MHz output of many sources or distribution amps in the form of a sinewave? Is it something to do with signal reflections or ease of isolation? Since zero crossing detectors are susceptible to noise wouldn't a fast TTL square wave be more appropriate for signal distribution within a equipment rack? The advantage of a sine wave is that you have a single, bounded frequency. A square wave has quite strong components at odd multiples of the base frequency, theoretically going up to infinity. To get a good shape of the signal you need at least the first three of the harmonics, resulting in a seven times increased bandwidth need. Beside of the more complicated handling of the higher frequency components, you also have to think about dispersion of the signal if you go trough filters or use longer cables. Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Why a 10MHz sinewave output?
On 2/6/12 6:14 AM, paul swed wrote: Indeed the long cable runs are tough. Though today we have differential cable drivers that do quite well to the Ghz range. But certainly back in the dark ages the sine wave was a very reasonable way to go. Regards Paul we may have GHz bandwidth drivers, but that doesn't solve the issue of frequency dependent propagation through a cable. At lowish frequencies (100 MHz) I'd suspect that the difference is more one of amplitude than phase, but still, it's something that has to be dealt with. One could just have a narrow band filter at the receiving end to pick up only the fundamental, but then, why not just send only the fundamental. ___ 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] Why a 10MHz sinewave output?
Well right you are thats why todays chips have equalizers and such. But then its all getting crazy complicated even though its in a itty bitty chip. My distribution is made of high quality television analog amps and I have in general made amplifiers and such with parts I can still easily pickup and solder to. But still I always do wonder about tinkering with a square wave dist system. Though I doubt I will ever actually do anything. KISS is the general principal. Regards Paul. On Mon, Feb 6, 2012 at 9:37 AM, Jim Lux jim...@earthlink.net wrote: On 2/6/12 6:14 AM, paul swed wrote: Indeed the long cable runs are tough. Though today we have differential cable drivers that do quite well to the Ghz range. But certainly back in the dark ages the sine wave was a very reasonable way to go. Regards Paul we may have GHz bandwidth drivers, but that doesn't solve the issue of frequency dependent propagation through a cable. At lowish frequencies (100 MHz) I'd suspect that the difference is more one of amplitude than phase, but still, it's something that has to be dealt with. One could just have a narrow band filter at the receiving end to pick up only the fundamental, but then, why not just send only the fundamental. __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://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] Why a 10MHz sinewave output?
On 2/6/12 6:47 AM, paul swed wrote: Well right you are thats why todays chips have equalizers and such. But then its all getting crazy complicated even though its in a itty bitty chip. My distribution is made of high quality television analog amps and I have in general made amplifiers and such with parts I can still easily pickup and solder to. But still I always do wonder about tinkering with a square wave dist system. Though I doubt I will ever actually do anything. KISS is the general principal. Regards Paul. adaptive equalizer and precision frequency/time distribution are going to be very uneasy bedfellows.. Of course, if you're just looking for distribution of house black burst or analog video, that's probably ok. You're looking for good waveform fidelity, rather than precise knowledge of time delays. In most of the precision measurement systems I fool with we look for parts in 1E10 or better. Say, 1 degree of phase at 32 GHz.. if you're multiplying up from a 10 MHz reference for that, the x3200 multiplication means you need to be pretty savvy about how your references are distributed (and, as well, how a phase change in the harmonic content might screw up the zero crossings) ___ 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] Why a 10MHz sinewave output?
Jim I want to be careful this is not my thread. the question came up. Why sine wave. Though I do appreciate your comments. Regards On Mon, Feb 6, 2012 at 10:26 AM, Jim Lux jim...@earthlink.net wrote: On 2/6/12 6:47 AM, paul swed wrote: Well right you are thats why todays chips have equalizers and such. But then its all getting crazy complicated even though its in a itty bitty chip. My distribution is made of high quality television analog amps and I have in general made amplifiers and such with parts I can still easily pickup and solder to. But still I always do wonder about tinkering with a square wave dist system. Though I doubt I will ever actually do anything. KISS is the general principal. Regards Paul. adaptive equalizer and precision frequency/time distribution are going to be very uneasy bedfellows.. Of course, if you're just looking for distribution of house black burst or analog video, that's probably ok. You're looking for good waveform fidelity, rather than precise knowledge of time delays. In most of the precision measurement systems I fool with we look for parts in 1E10 or better. Say, 1 degree of phase at 32 GHz.. if you're multiplying up from a 10 MHz reference for that, the x3200 multiplication means you need to be pretty savvy about how your references are distributed (and, as well, how a phase change in the harmonic content might screw up the zero crossings) __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://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] Why a 10MHz sinewave output?
Hi In addition to the stuff already mentioned, there's one more reason: RFI If you want to run around with a 10 MHz square wave with 1 ns rise time edges, it's going to have energy all over the place. To keep the rise time you will get well into the GHz. That may (as in probably will) interfere with a lot of RF measurements. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of bob grant Sent: Sunday, February 05, 2012 10:50 PM To: time-nuts@febo.com Subject: [time-nuts] Why a 10MHz sinewave output? Why is 10MHz output of many sources or distribution amps in the form of a sinewave? Is it something to do with signal reflections or ease of isolation? Since zero crossing detectors are susceptible to noise wouldn't a fast TTL square wave be more appropriate for signal distribution within a equipment rack? -- http://www.fastmail.fm - Send your email first class ___ 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] Why a 10MHz sinewave output?
Hi Differential signaling does indeed take care of a bunch of stuff. The gotcha is that both sender and receiver need to agree on levels and stuff like that. Most of these logic families have pretty short life spans if you include supply voltage dependant stuff. Could you work it out over the decades - yes. Would it be a pain to do 1960's style stuff today - yes again. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of paul swed Sent: Monday, February 06, 2012 9:15 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Why a 10MHz sinewave output? Indeed the long cable runs are tough. Though today we have differential cable drivers that do quite well to the Ghz range. But certainly back in the dark ages the sine wave was a very reasonable way to go. Regards Paul On Mon, Feb 6, 2012 at 3:56 AM, Attila Kinali att...@kinali.ch wrote: On Sun, 05 Feb 2012 19:50:28 -0800 bob grant bobgr...@fastmail.fm wrote: Why is 10MHz output of many sources or distribution amps in the form of a sinewave? Is it something to do with signal reflections or ease of isolation? Since zero crossing detectors are susceptible to noise wouldn't a fast TTL square wave be more appropriate for signal distribution within a equipment rack? The advantage of a sine wave is that you have a single, bounded frequency. A square wave has quite strong components at odd multiples of the base frequency, theoretically going up to infinity. To get a good shape of the signal you need at least the first three of the harmonics, resulting in a seven times increased bandwidth need. Beside of the more complicated handling of the higher frequency components, you also have to think about dispersion of the signal if you go trough filters or use longer cables. Attila Kinali -- The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap -- Tirin, The Dispossessed, U. Le Guin ___ 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] Why a 10MHz sinewave output?
bob grant wrote: Why is 10MHz output of many sources or distribution amps in the form of a sinewave? Is it something to do with signal reflections or ease of isolation? Since zero crossing detectors are susceptible to noise wouldn't a fast TTL square wave be more appropriate for signal distribution within a equipment rack? The preferred solution is to stick with a sine wave, but increase the frequency to 100 MHz or even 1 GHz if a 10 MHz sine wave is inadequate. Rick ___ 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] Why a 10MHz sinewave output?
As mentioned below, the propagation speed of the various harmonics varies. What also varies is the temperature coefficient of propagation speed. This, taken with imperfect impedance matches, yields complicated variation of zero-crossing times with temperature. The tempcos are particularly large below about 60 MHz, so operation at 100 MHz is helpful. The ratio of tempcos is about 2:1. Joe Gwinn Ref: “Environmental Effects in Mixers and Frequency Distribution Systems”, L.M.Nelson and F.L.Walls, NIST, 1992 IEEE Frequency Control Symposium, pages 831-837. time-nuts-boun...@febo.com wrote on 02/06/2012 09:37:59 AM: From: Jim Lux jim...@earthlink.net To: time-nuts@febo.com Date: 02/06/2012 09:38 AM Subject: Re: [time-nuts] Why a 10MHz sinewave output? Sent by: time-nuts-boun...@febo.com On 2/6/12 6:14 AM, paul swed wrote: Indeed the long cable runs are tough. Though today we have differential cable drivers that do quite well to the Ghz range. But certainly back in the dark ages the sine wave was a very reasonable way to go. Regards Paul we may have GHz bandwidth drivers, but that doesn't solve the issue of frequency dependent propagation through a cable. At lowish frequencies (100 MHz) I'd suspect that the difference is more one of amplitude than phase, but still, it's something that has to be dealt with. One could just have a narrow band filter at the receiving end to pick up only the fundamental, but then, why not just send only the fundamental. ___ 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] Why a 10MHz sinewave output?
Some sine-wave outputs are not very symmetrical, in that the rising edges are much more sinusoidal in shape than the falling edges. I guess my question is really about what type of input circuity and drive level are most common and which signal shape would provide the lowest jitter. -- http://www.fastmail.fm - Access your email from home and the web ___ 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] Why a 10MHz sinewave output?
-Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts- boun...@febo.com] On Behalf Of bob grant Sent: Monday, February 06, 2012 12:41 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Why a 10MHz sinewave output? Some sine-wave outputs are not very symmetrical, in that the rising edges are much more sinusoidal in shape than the falling edges. I guess my question is really about what type of input circuity and drive level are most common and which signal shape would provide the lowest jitter. Most line receiver chips are fine for squaring up sine-wave signals that come in on a 50-ohm connection at +5 to +15 dBm. If you need fast 10 MHz edges, they are pretty easy to generate on demand without adding significant jitter. A two-transistor differential amp works well enough in almost every case. I think the answer to the why sines? question is a mixture of several points others have raised. 1, 5, 10, and now 100 MHz sine waves have all been used for reference-frequency distribution. Equipment that needs to be locked to a common reference does one of two things with that reference signal as soon as it enters the enclosure: they either fan it out for use where it's needed internally, or they phase lock their own internal oscillator to it. Before digital hardware became so prevalent, these applications -- either miscellaneous RF circuits or analog PLLs -- both tended to expect sine wave signals. Also, the signal would have originated in a crystal oscillator or similar source, where it would naturally be available as a sine. So it would have taken extra circuitry to square it up, potentially extra circuitry to filter it at the destination, and better cabling to transmit the harmonic-rich signal. Differential signaling was not yet in common use, and not entirely free to implement... and EMI is always a concern even with 10 MHz sines. If you don't use good double-shielded cabling for 10 MHz distribution, your lab environment will be full of 10 MHz energy from your house clock that is difficult to keep out of sensitive circuits. Things would be even worse if we were at risk of 'broadcasting' harmonics from 10 MHz to daylight. These days you might do things differently if starting from scratch, but there is so much infrastructure designed to generate, carry, and use 5/10 MHz fundamentals that these have become an entrenched standard. If there's a trend away from 5/10 MHz, it seems to be towards 100 MHz fundamental distribution. -- john ___ 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] Why a 10MHz sinewave output?
On 02/07/2012 01:02 AM, Jim Lux wrote: On 2/6/12 7:41 AM, paul swed wrote: Jim I want to be careful this is not my thread. the question came up. Why sine wave. Though I do appreciate your comments. Regards I think it boils down to it's easier to get high precision when you only have one frequency to worry about Oh... nothing really beats it's what customers traditionally asks for Squarewave out provides high slew-rate which reduces the effect of additional noise. Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
Hi When the customers started asking in the 1930's, generating a square wave at high frequency was not so easy…. Bob On Feb 6, 2012, at 7:20 PM, Magnus Danielson wrote: On 02/07/2012 01:02 AM, Jim Lux wrote: On 2/6/12 7:41 AM, paul swed wrote: Jim I want to be careful this is not my thread. the question came up. Why sine wave. Though I do appreciate your comments. Regards I think it boils down to it's easier to get high precision when you only have one frequency to worry about Oh... nothing really beats it's what customers traditionally asks for Squarewave out provides high slew-rate which reduces the effect of additional noise. Cheers, Magnus ___ 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] Why a 10MHz sinewave output?
mag...@rubidium.dyndns.org said: Oh... nothing really beats it's what customers traditionally asks for Squarewave out provides high slew-rate which reduces the effect of additional noise. Right. But if you have a single frequency you can easily filter out most of the noise. --- As clock speed has increased over the years, a new field has emerged. A good name is signal integrity. That covers clock distribution, data distribution, and power supply bypassing/regulation/decoupling. It's basically all the analog stuff needed to make digital logic work in the real world. The technology for distributing more bits is also useful for reducing noise/jitter. There are whole families of chips for clock distribution. Many include PLLs which can correct for trace length, make other frequencies, and/or do the spread spectrum thing to reduce EMI. The ones I'm familiar with are targeted at digital applications. Jitter within a small fraction of a bit cell is fine. The target market doesn't care about time-nut class super clean clocks. There are other families of chips (or parts of big chips) for driving/receiving clocks and data between boards/boxes. Most of those are now differential so I assume twisted pair is cheaper than coax. SATA between your motherboard and hard disk is a good example. It runs at 1.5, 3, or 6 gigabits/second. Wiki says up to 1 meter. If you want a good example of the technology in this area, check out gigabit ethernet over CAT5. It's 5 level encoding (2 bits/baud) at 125 megabaud/sec over 4 pair in both directions over each pair. Optical stuff is still single-ended. :) There are some very low cost optical links for distribution of audio. The key idea is to use plastic rather than glass. Bandwidth is limited but cost is low. -- These are my opinions, not necessarily my employer's. 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.
