Re: [Flexradio] A question on Frequency stability vs. Temperature
Bill Guyger wrote: Wouldn't this constitute a GROUND loop? Ok that was cruel and unusual punnishment. Pun ignored ;-) ... Would taking a small styro block, hollowing out one side and placing it over the oscillator be a quick and dirty (there's that word again) fix? It sure wouldn't be as stable as the more complex hardware and software tricks that have been tossed out for consideration lately, but it might be a KISS attack plan. Using a thermal insulator will certainly help to buffer you from ambient temperature variation, and might well stretch the oscillator's time constant from ~10 seconds to a few minutes. Personally, I have had very good luck using wide-mouthed thermos bottles. I have also found that wrapping an oscillator in bubble wrap and putting it in a cardboard box, or a cardboard box filled with plastic "peanuts" works as well as a block of Styrofoam and only takes a minute to build. But even then, your "heat sink" is the ambient air supply which probably cycles 10-20 degrees on a daily basis. My "hole in the ground" suggestion was simply a way to find a more stable heat sink. N8UR's statement about using a heated box also is a way to solve the problem. One thing to remember, which may not be totally obvious, is you use a heater element and a temp sensor, put the heat source and the sensor in close contact. Do not put the sensor at the oscillator inside some thermal insulation away from the heater -- this is guaranteed to give thermal overshoot with a cycle time related to the time constant of the insulation. 73, Tom
Re: [Flexradio] A question on Frequency stability vs. Temperature
KD5NWA wrote: The project being discussed for the Xylo is; 1. Thermal isolation with a accurate heater to reduce the drift. 2. Use the Xylo to connect to a GPS and have a accurate 1 pps clock 3. Use the 1 pps clock to measure the DDS 200MHz clock, integrate multiple reading to make for finer resolution. 4. Use the 1 pps clock to measure the A/D clock, take multiple readings also. 5. Feed the results to the PC who will proceed to correct the internal math so there is no drift. Let me suggest a different approach at step 3. Connect the DDS reference to a long counter (more than one second) -- it can be straight binary, and 32 bits is overkill. Use the 1PPS to strobe the counter into a register without stopping the counter (i.e. like lap timing with a stop watch). Then make your corrections based on accumulated phase, which can then be averaged over many seconds. 73, Tom
Re: [Flexradio] A question on Frequency stability vs. Temperature
John Ackermann N8UR wrote: Insulation will slow down the response to external temperature variations, but unless there's a heat source inside the insulated area, it won't prevent the change (sooner or later, the internal temperature will match the external). Almost true -- what you really want to do is to heat-sink the oscillator to a large thermal mass. In addition to a temperature controlled heater, another good heat sink is DIRT. If you were to dig a post-hole a few feet down into the earth and then drop the entire oscillator down the hole, and fill it back up, you would be amazed at the stability you achieve. We learned this trick in interferometry when we want to have stable microwave LOs out at the feed of several dishes. Even in the desert with a huge night/day cycling, we got good stability by burying the coax 1-2 feet. Tom
Re: [Flexradio] FW: A bit of light entertainment
K3IB wrote: Only those under 'old geezer' age who don't remember (or never heard of ) the LANG auld lang syne! There was a man, whose name was Lang, and he had a neon sign. And Mr Lang was very old, so they called it --- "Old Lang's Sign" HNY -- Tom
Re: [Flexradio] FW: A bit of light entertainment
Eric offered the sidebar: Guys don't forget my: Processor Technology Sol - 20 . . . We used to call them the Proctology-20. They went the way of the CommodeDoor C-64. I had a couple of Imsai's myself. I remeber my first 256 byte RAM card and writing a one-D PONG game for the front panel status switches. In mentioning classic languages, let's not forget DJ4ZC's IPS -- IPS is a threaded interpreter that has worked on a number of processors. Rad Hard Cosmac 1802's running IPS powered AO-10, AO-14 & AO-40. Karl ported IPS to the Atari 400 & 600, which served many of the AO-10/13 ground stations. W0PN/W1HDX/W3IWI did an 8080 port for command stations elsewhere who used S-100 based hardware. N4HY has just finished a 32-bit IPS for the upcoming P4D, P5A and Eagle missions. IPS is a really neat multi-tasking implementation of FORTH. -- 73, Tom
Re: [Flexradio] laptops
[EMAIL PROTECTED] wrote: Mine does not have a parallel port. I found the USB to Parallel adapter a satisfactory solution. It even has a narrow enough plug that you can put in a second USB peripheral above/below it if it, too, has the narrow type plug (many things don't). I offered my caveat emptor based on our (N4HY, AB2KT, W2GPS & I) experience in getting ANY of the USB => parallel widgets running in LINUX. For the testbed of the Software Defined Transponder (SDX), we used two SDR-1000s with LINUX based software tools for all the heavy horsepower DSP tasks. But we ended up needing to schlep two Windoze laptops just to handle the parallel port setup for the two SDR-1000s because we were spectacularly unsuccessful in getting the LINUX box to talk thru any USB widget we could find. I did manage to find a two-port Ethernet Print Server that Frank is trying to get working as a better solution to the problem. FYI -- Despite the frustration of needing to run three computers to make the SDX work (see the pictures at http://n4hy.smugmug.com/gallery/736793), the kludge SDX worked quite well. Audio from the first 3-way "QSO" can be heard at ftp://ftp.cnssys.com/pub/amsat/Eagle_SDT_1st_Contact.mp3. 73, Tom
Re: [Flexradio] laptops
Check to be sure that the laptop has a "real" parallel port -- few these days do. 73, Tom
Re: [Flexradio] FW: Impulse Wave file
richard allen wrote: In our military system tests we acquire 10-20 impulses and sum them in the frequency domain. If the ripple is actually in the system then it will stay in. This was what the generals all wanted. In our seismic stuff, where the geophysicists seem to think it is needed to find oil, we require the < 1 dB flatness in the frequency domain plateau of a single impulse. In the VLBI world, we continuously inject weak pulses at a 1 MHz rate (1 usec between pulses) which have rise times in the 10s of psec range. These pulses, injected into the radio astronomy receiver front ends, manifest themselves as a frequency rail every 1 MHz. To achieve a very wide (upwards of 1 GHz) flat passband, these "phase cal" signals are processed to determine the phase offset needed to bring them all into line. The pulse generator that Gerald built into the the SDR-1000 is my design, derived from the same concept. In the VLBI world, we adjust the pulse amplitude so that it only increases the wideband system temperature by only 1-2%, but the pulses are seen with good SNR as frequency rails in FFT analyzers running a few Hz bandwidth. 73, Tom
Re: [Flexradio] Frequency stability and calibration
Jim Lux wrote: There ARE actually sources with better close in phase noise than a quartz crystal, just in case you see one at a hamfest or surplus place (or, you're wealthy enough). A hydrogen maser, for instance (that's what we use at work, JPL, when we're concerned about such things.. but then we have an infrastructure to distribute the maser signal around, and a budget for the support staff). Actually, all H-Maser I know rely on a really high quality xtal for their short-term stability (and hence intrinsic phase noise); by high quality, I mean BVA xtal units costing in the $5k range. The transition from the BVA xtal to the maser is typically done at times ~30-100 seconds or so (see the AVARs in my tutorials I mention later, or http://www.leapsecond.com/museum/manyadev.gif to see that the BVA performance is better than the Maser up to ~30 seconds. The goal is to "hand off " from one oscillator to the next when their Allen deviation is equal). BTW -- we actually have a couple of "amateurs" that have both passive & active H-Masers in their basements. One is Tom vanBaak (no call) whose efforts can be viewed at http://leapsecond.com/ and another is Jim Jaeger (K8RQ) (see http://www.clockvault.com/ if you can stand the music!). TvB offered a review paper on amateur timekeeping at the 2003 PTTI meeting, which can be fetched at http://tycho.usno.navy.mil/ptti/ptti2003/paper35.pdf. Also be sure to note TvB's "Most Accurate WristWatch" when you log onto leapsecond.com. I've said it before, and I'll repeat it now -- you are better off thinking in the frequency (and phase noise) domain when you are considering oscillators on time scales shorter than tens of seconds, and in the time domain for minutes and longer. If you are interested in these topics, you might want to fetch one of my "Timing for VLBI" tutorials at http://gpstime.com/ . In my past incarnation I ran NASA's Geodetic VLBI program and was responsible for H-masers as time and frequency standards. While I am on here making comments on this thread, I note that Alberto, I2PHD is using a circuit similar to the one I developed for locking an xtal to the 10 kHz output from the Connexant/Navman Jupiter-T receiver. A couple of notes on what I found: My initial effort also used 74HC390 dividers as a ripple counter to get from 10 MHz -> 10 kHz. But I found that the propagation delay thru these dividers varied strongly with temperature, amounting to a couple of hundred nsec in a day. I fixed this problem by using a simple, but elegant circuit developed by Tom van Baak (see http://www.leapsecond.com/tools/ppsdiv.zip) which uses a PIC with its clock input driven by the 10 MHz signal and a finite state machine that executes a fixed number of instructions to generate lower frequencies. Not only is it a very stable synchronous divider, but also it need only a couple of $$ worth of parts. I did a lot of work to optimize loop time constants to try to achieve performance at the couple of nsec levels. Most of the time, the Jupiter-T steered the oscillator very well, but about once per hour, the 10 kpps (and 1pps) output sawtooth goes thru a zero-beat, with a fixed bias error spanning intervals of 10s of seconds. You can see some of these sawtooth "hanging bridges" that really screw up the locking in my tutorials on gpstime.com. And you can see the fix that Rick (W2GPS) is using in his latest CNS clock using the M12+ in the latest of the gpstime.com tutorials. 73, Tom
Re: [Flexradio] Frequency stability and calibration
In all this, please remember that there are TWO oscillators involved: The SDR-1000's internal LO, derived from the 200 MHz xtal via the DDS chip, and the sampling clock on the sound card A/D converter. Oscillator #1 will give an error that is proportional to the RF signal frequency. In the discussions in this thread, this is the oscillator that's being talked about. Oscillator #2 produces an error that is independent of RF frequency. But this is derived from the rather cheap xtal that is inside the guts of your PC, hardly the environment most conducive to high stability. Since you have two unknown oscillators, you must observe a reference on (at least) two frequencies, hopefully widely separated in order to calibrate both oscillators. And both of the two oscillator frequencies need to be included in the software entry of oscillator error. It's a real pity that there is no easy way to tame the sampling clock accuracy. --- On a related topic, let me again reiterate a point I made a few months ago. It is possible to send an external (most likely 10.000 MHz) reference into the DDS chip by simply replacing the 200 MHz oscillator chip; Gerald sells a kit with a 4-pin header and a short piece of coax to make this modification easier, and the software lets you set up a PLL on the DDS chip to serve as a x20 frequency multiplier. With this mod installed, you can make Oscillator #1 be more ACCURATE than the supplied oscillator. However, I would recommend against this approach. The 200 MHz xtal oscillator was chosen as a PRECISION oscillator #1 with very low phase noise. The digital PLL on the DDS chip associated with the x20 multiplier has more phase noise, which will in turn hurt the SDR1000's superb receiver characteristics. You might not notice it at first, but the effect will be to spread out undesired (off-frequency) signals into the desired passband. If you are operating in a multi-multi environment you will really know the difference. You invested many extra bux in the fancy Delta-44 sound card to improve the intermod characteristics -- why waste that performance with an increase in the phase noise floor :-\ ? !!! 73, Tom
Re: [Flexradio] A simple fan noise abatement modification
Paul Wade W1GHZ wrote: another way to reduce fan noise is to reduce the speed of the fan. one of my recent projects is a fan controller with speed proportional to temperature, with the temp sensor wherever you like. A number of 12VDC computer fans (I'm looking at one right now branded "ThermalTake") come with speed control capabilities built in -- either from a pot or a thermistor that they supply with the fans. I use the pot variety on my PC and "tune" the speed for minimum noise. 73, Tom
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
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] ARRL review and the D44
José Dumoulin wrote: Hi Gerald es All The photo of the breakout box shows an orange plug of the Hosa cable going to out 1. Is it a test of our vigilance ? If yes, I won. You aren't the sole winner, José -- I saw it too. What you see is the secret patent-pending Hilbert Transformer used to invert sidebands :-X 73, Tom
