[Flexradio] Ext. Reference clock kit
Title: Ext. Reference clock kit I was wondering if anyone is using a GPS to generate the 10 or 20 MHz frequency reference used with the external reference clock kit? If so, how did you do it? I have a GPS receiver (hockey puck, NEMA output) that I'd like to use for this if it is possible. -Tim --- Tim Ellison Integrated Technical Services Apex, NC USA 919.674.0044 Ext. 25 / 919.674.0045 (FAX) 919.215.6375 - cell PGP public key available at all public KeyServers
Re: [Flexradio] Ext. Reference clock kit
richard allen wrote: Message (snip) It provides accuracy of better that 1 part in 10**(-10) or 1 Hz at 10 GHz. Its 10 MHz output will drive the little conversion kit for the sdr1k available from FlexRadio. One word of caution. When 10 MHz is fed into the same socket as the present 200 MHz xtal oscillator on the DDS, the DDS is then re-programed to have its internal PLL make the 200 MHz signal. This PLL has poorer short-term stability than the Xtal, which in turn means that the close-in phase noise will increase. This phase noise in turn decreases the dynamic range, and it will probably be unacceptable in a multi-multi contest station! A much better option is to replace the 200 MHz xtal with a clean 100 or 200 MHz source. TAPR is working on a lock box that should work well which would allow you to transer the stability of the GPS or Rubidium clock into the SDR-1000 without causing undue phase noise. 73 de Tom, W3IWI
Re: [Flexradio] Ext. Reference clock kit
Title: Message Tom et al Youse guys are going to get Jim Lux into this again! (REALLY do love your comments Jim). This is probably a do-able topic for early next year. Hey! Why not long term aging, and Loran. Not kidding. Anything is possible in software with a hardware assist, including Internet NTS corrections. We have our GPS receivers poised. What we need is a designer! You game? We are NOT going for 10 mhz multiplied, but 1 cycle or so at 200 mhz! Eric2 AA4SW From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Clark, W3IWI Sent: Tuesday, September 06, 2005 7:46 PM To: FlexRadio@flex-radio.biz Subject: Re: [Flexradio] Ext. Reference clock kit richard allen wrote: (snip) It provides accuracy of better that 1 part in 10**(-10) or 1 Hz at 10 GHz. Its 10 MHz output will drive the little conversion kit for the sdr1k available from FlexRadio. One word of caution. When 10 MHz is fed into the same socket as the present 200 MHz xtal oscillator on the DDS, the DDS is then re-programed to have its internal PLL make the 200 MHz signal. This PLL has poorer short-term stability than the Xtal, which in turn means that the close-in phase noise will increase. This phase noise in turn decreases the dynamic range, and it will probably be unacceptable in a multi-multi contest station! A much better option is to replace the 200 MHz xtal with a clean 100 or 200 MHz source. TAPR is working on a lock box that should work well which would allow you to transer the stability of the GPS or Rubidium clock into the SDR-1000 without causing undue phase noise. 73 de Tom, W3IWI
Re: [Flexradio] Ext. Reference clock kit
I would just echo Tom's comments... you're much better off using the GPS to discipline a 200 MHz source. An even easier way is to put your (quiet) 200 MHz oscillator in a separate box (pref ovenized, but not necessarily), and then count it against the GPS tick (or the 10MHz from your Z3801). Use the counts to adjust the frequency you tune the radio to. My measurements on a box-stock early SDR1K showed frequency changes on the order of 0.1 ppm per second, and if you take out the linear trend, it's about 1% of that. In Hertz, 0.1ppm is 20 Hz on a 200 MHz source. Most of the drift is thermal, so just getting the oscillator away from the radio would help a lot. Philosophically, if you can avoid needing to steer your oscillator, that has two advantages: 1) The tuning pin doesn't provide an additional noise-frequency change path 2) The crystal can be higher Q, because it doesn't need to be adjustable. Nice quiet SC cut crystal is probably what you want, and put it in a reasonably temperature stable box, and then let it age and just track out the aging. Jim At 05:21 PM 9/6/2005, ecellison wrote: Tom et al Youse guys are going to get Jim Lux into this again! (REALLY do love your comments Jim). This is probably a do-able topic for early next year. Hey! Why not long term aging, and Loran. Not kidding. Anything is possible in software with a hardware assist, including Internet NTS corrections. We have our GPS receivers poised. What we need is a designer! You game? We are NOT going for 10 mhz multiplied, but 1 cycle or so at 200 mhz! Eric2 AA4SW From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Tom Clark, W3IWI Sent: Tuesday, September 06, 2005 7:46 PM To: FlexRadio@flex-radio.biz Subject: Re: [Flexradio] Ext. Reference clock kit richard allen wrote: (snip) It provides accuracy of better that 1 part in 10**(-10) or 1 Hz at 10 GHz. Its 10 MHz output will drive the little conversion kit for the sdr1k available from FlexRadio. One word of caution. When 10 MHz is fed into the same socket as the present 200 MHz xtal oscillator on the DDS, the DDS is then re-programed to have its internal PLL make the 200 MHz signal. This PLL has poorer short-term stability than the Xtal, which in turn means that the close-in phase noise will increase. This phase noise in turn decreases the dynamic range, and it will probably be unacceptable in a multi-multi contest station! A much better option is to replace the 200 MHz xtal with a clean 100 or 200 MHz source. TAPR is working on a lock box that should work well which would allow you to transer the stability of the GPS or Rubidium clock into the SDR-1000 without causing undue phase noise. 73 de Tom, W3IWI ___ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz James Lux, P.E. Spacecraft Radio Frequency Subsystems Group Flight Communications Systems Section Jet Propulsion Laboratory, Mail Stop 161-213 4800 Oak Grove Drive Pasadena CA 91109 tel: (818)354-2075 fax: (818)393-6875
Re: [Flexradio] Hardware interface (Linux)
Jim Lux wrote: Which of the two hardware wrappers is the current one in dttsp (the one in pyhw or pyhw2?) pyhw2 is the current version. I am informed that there are some conflicts in the way it's initialized that I have been unable to duplicate here. It's supposed to be backward compatible with all versions of the SDR hardware. Either way, I have a suggestion for partitioning the hardware wrapper. This code is as literal a transposition from the PowerSDR C# as possible. Put the PC sound card specific stuff in the other (sample rate, FFT size) extern int getSampleRate(void); extern void setSampleRate(int value); extern int getFFTLength(void); extern void setFFTLength(int value); These are vestigial entries from the PowerSDR code. They are non-functional in the Linux version. No further work is going to be done on this code. It will be replaced by a different structure based on a hardware abstraction layer. 73 Frank AB2KT
Re: [Flexradio] Ext. Reference clock kit
Jim I knew i could bait you! (smile). I am sort of gobbled up by this precision thing! I do have my GPS receiver and am ready for the 1 part to the -13 (give or take a couple of exponents!). Can we take the 200 mhz standard out of the SDR 1000 as is? Actually I visit WWV frequently with the phase display, from 20 meters, where I been operating, and am actually pretty pleased with the long term accuracy of the radio. Course I fall asleep and leave it on. Eric From: Jim Lux [mailto:[EMAIL PROTECTED] Sent: Tuesday, September 06, 2005 8:38 PM To: ecellison; [EMAIL PROTECTED]; FlexRadio@flex-radio.biz Subject: Re: [Flexradio] Ext. Reference clock kit I would just echo Tom's comments... you're much better off using the GPS to discipline a 200 MHz source. An even easier way is to put your (quiet) 200 MHz oscillator in a separate box (pref ovenized, but not necessarily), and then count it against the GPS tick (or the 10MHz from your Z3801). Use the counts to adjust the frequency you tune the radio to. My measurements on a box-stock early SDR1K showed frequency changes on the order of 0.1 ppm per second, and if you take out the linear trend, it's about 1% of that. In Hertz, 0.1ppm is 20 Hz on a 200 MHz source. Most of the drift is thermal, so just getting the oscillator away from the radio would help a lot. Philosophically, if you can avoid needing to steer your oscillator, that has two advantages: 1) The tuning pin doesn't provide an additional noise-frequency change path 2) The crystal can be higher Q, because it doesn't need to be adjustable. Nice quiet SC cut crystal is probably what you want, and put it in a reasonably temperature stable box, and then let it age and just track out the aging. Jim At 05:21 PM 9/6/2005, ecellison wrote: Tom et al Youse guys are going to get Jim Lux into this again! (REALLY do love your comments Jim). This is probably a do-able topic for early next year. Hey! Why not long term aging, and Loran. Not kidding. Anything is possible in software with a hardware assist, including Internet NTS corrections. We have our GPS receivers poised. What we need is a designer! You game? We are NOT going for 10 mhz multiplied, but 1 cycle or so at 200 mhz! Eric2 AA4SW From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Tom Clark, W3IWI Sent: Tuesday, September 06, 2005 7:46 PM To: FlexRadio@flex-radio.biz Subject: Re: [Flexradio] Ext. Reference clock kit richard allen wrote: (snip) It provides accuracy of better that 1 part in 10**(-10) or 1 Hz at 10 GHz. Its 10 MHz output will drive the little conversion kit for the sdr1k available from FlexRadio. One word of caution. When 10 MHz is fed into the same socket as the present 200 MHz xtal oscillator on the DDS, the DDS is then re-programed to have its internal PLL make the 200 MHz signal. This PLL has poorer short-term stability than the Xtal, which in turn means that the close-in phase noise will increase. This phase noise in turn decreases the dynamic range, and it will probably be unacceptable in a multi-multi contest station! A much better option is to replace the 200 MHz xtal with a clean 100 or 200 MHz source. TAPR is working on a lock box that should work well which would allow you to transer the stability of the GPS or Rubidium clock into the SDR-1000 without causing undue phase noise. 73 de Tom, W3IWI ___ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz James Lux, P.E. Spacecraft Radio Frequency Subsystems Group Flight Communications Systems Section Jet Propulsion Laboratory, Mail Stop 161-213 4800 Oak Grove Drive Pasadena CA 91109 tel: (818)354-2075 fax: (818)393-6875
Re: [Flexradio] Ext. Reference clock kit
Philosophically, if you can avoid needing to steer your oscillator, that has two advantages: 1) The tuning pin doesn't provide an additional noise-frequency change path 2) The crystal can be higher Q, because it doesn't need to be adjustable. Sounds like an application for the Huff'n'Puff stryleof stabilzer... 73, Lyle KK7P
Re: [Flexradio] Ext. Reference clock kit
Lyle Been out of it for a while. Maybe I'm being duped, but what the heck I s a Huff'n'Puff? !!! Eric -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Lyle Johnson Sent: Tuesday, September 06, 2005 8:55 PM To: FlexRadio@flex-radio.biz Subject: Re: [Flexradio] Ext. Reference clock kit Philosophically, if you can avoid needing to steer your oscillator, that has two advantages: 1) The tuning pin doesn't provide an additional noise-frequency change path 2) The crystal can be higher Q, because it doesn't need to be adjustable. Sounds like an application for the Huff'n'Puff stryleof stabilzer... 73, Lyle KK7P ___ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz
Re: [Flexradio] Ext. Reference clock kit
Been out of it for a while. Maybe I'm being duped, but what the heck I s a Huff'n'Puff? !!! It is a means of gently stabilizing an oscillator. It requires the oscillator to be reasonably stable already. There are several examples of this sort of circuit, pioneered by PA0KSB back in the early 1970's. See http://www.hanssummers.com/radio/huffpuff/index.htm for some references and links. 73, Lyle KK7P
Re: [Flexradio] Ext. Reference clock kit
Lyle Tnanks ... Readin Eric2 -Original Message- From: Lyle Johnson [mailto:[EMAIL PROTECTED] Sent: Tuesday, September 06, 2005 9:11 PM To: ecellison Cc: FlexRadio@flex-radio.biz Subject: Re: [Flexradio] Ext. Reference clock kit Been out of it for a while. Maybe I'm being duped, but what the heck I s a Huff'n'Puff? !!! It is a means of gently stabilizing an oscillator. It requires the oscillator to be reasonably stable already. There are several examples of this sort of circuit, pioneered by PA0KSB back in the early 1970's. See http://www.hanssummers.com/radio/huffpuff/index.htm for some references and links. 73, Lyle KK7P
Re: [Flexradio] Ext. Reference clock kit
Eric wrote: Message Tom et al Youse guys are going to get Jim Lux into this again! (REALLY do love your comments Jim). This is probably a do-able topic for early next year. Hey! Why not long term aging, and Loran. Not kidding. Anything is possible in software with a hardware assist, including Internet NTS corrections. We have our GPS receivers poised. What we need is a designer! You game? We are NOT going for 10 mhz multiplied, but 1 cycle or so at 200 mhz! Try this as a mostly software solution: If you were to feed the 200 MHz xtal into a long counter (i.e. 32 bits, with a total count of 2^32=4.3e9), the counter will "wrap" every ~ 21.5 seconds (with LSB = 5 nsec). Every so often (frequent enough so that you don't lose track of which 21+ second ambiguity cycle you are on), strobe the count into a register. The idea will be to use the integrated count (including the n*21+ second cycles) to establish the average clock rate. To give you an idea about how good a cheap GPS receiver can be as a clock, surf to http://gpstime.com/ and take a look at my various GPS timing papers (ION 2000 the last VLBI workshop are good starting places) and at Rick's M12+ receiver evaluation. Averaging over as few as 5-10 cycles (a couple of minutes) will tell you the error in the 200 MHz clock frequency to 1:10e10. In the SDR you already have a "handle" to correct the number cranked into the DDS to achieve a desired signal frequency -- this simply changes the phase increment number cranked into the DDS chips integrators. With only the addition of a simple counter register driven by the 200 MHz xtal (the jitter of it sets the phase noise floor) and a good GPS receiver, you have the ability to "steer" the master oscillator without the need for D/A converters totally in $oftware. Without a GPS receiver, with a good, stable NTP server, you should be able to keep you computer's clock accurate at the 10-20 msec level. Just using it to grab a counter sample, over 1 day you will have enough resolution to "track" the 200 MHz error at a level ~1:10e7 (i.e. 10 Hz @ 100 MHz) without even using a GPS receiver. Even the grubbiest GPS receiver, not designed at all for precision timing, will provide timing at the 1 usec level (even when navigating to give a 3D position); combine this with a 15 minute average (~1000 seconds) gets you 1:10e8. All this only leaves the sound card's sample clock as an undefined "local oscillator" in the chain and that remains as a fixed frequency offset that you take out as a constant by listening to WWV. This will continue to be an annoyance until someone comes up with an external sampling clock input for the sound card. Now for a really hair-brained extension: The sound card clock offset could be removed in the middle of the passband if, instead of using a ~11 kHz "IF" as the offset of the 1st LO, you were do a true "zero IF" receiver, and let the FFT handle suppression of the unwanted sideband. I get the impression that the Delta-44 is close enough to being an "ideal" A/D converter that the "DC" hole in the middle of the passband might not be such a problem. If you can go to a "zero IF" receiver, then any error in the sound card's sampling frequency will only effect the apparent offset signals away from the "DC" middle of the passband. It's fun to speculate on these ideas! 73, Tom
