[time-nuts] GPSDO PLL Loop Filter Values
Hi, I'm cobbling together a very basic PLL GPSDO with components I have to hand which means I'm pushing my luck as far as the loop filter values are concerned. These are - N = 1000 (10kHz ref from a Jupiter-T), Kv = 27Hz/V (10MHz Motorola VC-TCXO), Kp = 0.4V/rad from a 74HCT9046 type-II PD with charge-pump. >From these I've worked out some values graphically and with a couple of apps I've found. They are an old DOS program by KD9JQ and a web one at - http://www.aubraux.com/design/pll-design-tool.php The first tells me I need some gain between the loop-filter and the VCO, the second (the third order active choice) seems (I think) to have the capacitor values the wrong way round. My own efforts suggest I can get away with the values I've calculated but with a lower loop bandwidth and longer lock-up time than I'd like. The op-amp I'll be using for the filter, or extra DC gain for the VCO, will be an OPA-703. How badly would sticking a gain block between the filter and the VCO screw things up noise-wise (if at all)? Any thoughts on getting out of the 'low resource' hole I've dug would also be much appreciated. BTW, I'm not pushing any envelopes and my previous projects, with different components, have worked out reasonably well Cheers - Joe G3LLV ___ 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] Info Needed on MOT KX1516AA VC-TCXO
Hi, I have some Motorola K1516AA, 10MHz, VC-TXCO devices (date-coded 1988) but with only a basic pin-out diagram to their name and am wondering if anyone knows a little more about them. Specifically I'm concerned with the apparent high output-Z which means that a sniff of 'C' or a tad of loading drags down the output to a fraction of the off-load value. Unless they were made for a very specific purpose, this characteristic would seem to me as pointless. Also, by measurement and experimentation, I'm fairly sure that they don't use an open collector or emitter follower output port. They may work as a current source but I haven't gone that route as yet. TIA - Joe G3LLV ___ 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] ABC time signals in Tasmania/Australia wrong
Hi, I don't know whether the ABC signal you are referring to is TV, AM, FM or DAB but, if it is digitally networked, it isn't uncommon for time signals to be out by a second or so. Before Christmas, here in Sheffield (UK), the digital clock on my bedside DAB radio was well over seven seconds slow but suddenly 'pulled-in' to about two or so. When I first got the radio, I rang the local manufacturer's 'Help Line' to be given the two-word answer "Network Delays". Some of these will be unavoidable but I seem to remember reading that they are also something to do with synchronisation of, or preventing interference from, multiplexes in nearby areas. It would be nice if the offset were constant though but perhaps is set dynamically. First off I wondered if they couldn't have preset the local transmitter clock to take this into account but realised that it would then insert the 'pips' at the wrong place in the audio stream. Still, if they can put GPS disciplined clocks at mobile phone sites, they should be able to set the local time bytes to better than two seconds. If someone has more information on this I would like to hear it? A few years back you could email the BBC engineering department but now it's all out to contract and I've no idea who to ask. Cheers - Joe G3LLV Date: Sun, 3 Jan 2010 19:02:18 +1100 From: "Morris Odell" Subject: Re: [time-nuts] ABC time signals in Tasmania/Australia wrong To: Message-ID: <01ca8c4b$11f5fcd0$35e1f6...@net.au> Content-Type: text/plain;charset="us-ascii" They appear to be spot-on here in Melbourne. Morris Date: Sun, 3 Jan 2010 12:14:05 +1100 From: Jim Palfreyman Subject: [time-nuts] ABC time signals in Tasmania/Australia wrong For the Down Under nuts, The ABC radio time signals in Hobart are one second out. Is it a national thing? Can others in the country check? I rang the ABC locally on xmas eve but it is still not fixed. Jim Palfreyman ___ 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] SocketWatch Woes
Hi, Does anyone on the list use SocketWatch to keep their computer's clock roughly up to snuff time-wise? With me having switched to Vista (and lately W7), it often can't make the necessary network connection and gives me 'access denied' messages. The strange thing is that it will work fine from a new installation but soon runs out of puff; maybe within the hour or within the day. Perhaps I haven't ticked the right boxes, so any pointers in this direction would be appreciated as there is no sign of any support for it. Yes, I know there are other products which do much the same thing but I've been using this utility for years and have become attached to it. Also I've got $10 invested in it and my mattress is empty :-) Cheers - Joe G3LLV ___ 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] Egg on Face (was EPE - GPS Frequency Reference Project)
Hi, >There's a subtle difference between 3rd phase detectors in the 74HC4046A >(Philips/NXP, ON, TI) and the 74HC4046 (Fairchild, NS) >The 3rd Phase detector in the 74HC4046A works as the designer intended >in the GPSDO circuit, the 3rd phase detector in the 74HC4046 does not. >The 74HC4046 uses an RS flipflop for the 3rd phase detector and requires >narrow pulses on the R and S inputs. >The 74HC4046A uses extra internal gates to ensure that only narrow >pulses are seen by the RS flipflop in the 3rd phase detector. >Bruce You are perfectly correct. I hadn't noticed that there was a 74HC4046A fitted to the board in the article but just a plain 74HC4046 shown in the parts list. However, it is something to watch out for as this will be a popular project among those, like myself, who do not need to slice time quite so finely. Cheers - Joe G3LLV ___ 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] EPE - GPS Frequency Reference Project
Hi, Boring mode - ON With reference to the subject matter and my previous posting, I can confirm in the true Orwellian manner that all 74HC4046 devices are equal except that some are more equal than others. Mine, a NS labeled device, will not tolerate DC coupling along with long pulse inputs whereas others (I think those from NXP [Philips]) will. Another, but messy solution, is to AC couple them and clamp the negative-going peaks to ground. Boring mode - OFF Cheers - Joe G3LLV ___ 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] I'm all of a dither.
Hi, A fellow amateur and I have just put together the GPS-based frequency reference published in the "Every day Practical Electronics" issue of April/May 2009 and are both experiencing the same problem. The type-3 phase comparator of the 74HC4046 has both 1-pps and 50kHz DC-coupled inputs designed to produce an error pulse due to the difference between their leading edges. However, the longer pulse dominates the output because it holds the latch in thrall despite the 50kHz pulse trying to grab a little of the action. My question is then, are there variants of the 74HC4046 that have a type-3 detector which is edge-drive only? Natch, I can AC-couple and clamp them but I just wondered. I know that in the past that there have been differing versions of the old CD4046 and now, of course, there are also the '7046 and '9046 types around. Cheers - Joe G3LLV ___ 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] Racal 1992
Hi, A year or so back I had an unusual fault on my 1991 (160MHz version of the 1992). After half-an-hour it would lock-up if you changed any settings but was okay if you left it alone. Of course, after a cool-down period, all went well until the next time. Now for some reason I got it into my head that it was the GPIB board giving me grief so I put the 10x scope probe on a buss line going to it from IC18 on the motherboard. Instantly the fault appeared and it then became apparent there wasn't enough poke to run both the counter and the few pF of the scope lead. To cut a long story short, the supply pin was bent under at 90 degrees so the chip was working without any external power, just on internal leakages, until it warmed up. Had it been IC18 - good bye Mr. Chips. Cheers - Joe G3LLV ___ 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] OT: AC voltage standard
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Hi, Excuse the topic but is does push the same buttons as it were. After calibrating my old HP54502A 6-bit digitizing scope I'm left with an error I can't quite believe and so am trying to determine which of my instruments is telling me lies. Anyone know of a simple way of producing an AC voltage standard suitable for general workshop use without reference to another one? About one percent would be good enough, wave shape and frequency accuracy not important (wash my mouth out). I have a Weston Cell for DC voltage calibration, a Rb one for frequency but nothing for AC volts. Perhaps there is a chip out there that clocks between accurate limits that I could use as a source? Thanks - Joe ___ 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] Rubidium stability
Jerry, >Is this variability more likely due to the rubidium source (failing bulb) or >due to problems with the 5334B counter? Obviously you need a third source for comparison while locking your counter to the Rb source. I gather from the web that the Lucent unit uses an Efratom module in which case there should be a lamp voltage display or at least a measurement pin for it available somewhere. I posted an old Efratom FRK manual to BAMA some time ago which may give you a clue. A good lamp will show better than 5V although this is actually the voltage on the output of the photo-detector amp. New lamps are available on the web although I replaced mine in a Racal 9475 Rb standard some time ago with no obvious improvement; it still reads 5.8V when the manual says it should be between 6 and 12V. I was told once that varnish can slowly evaporate onto the cell window thus reducing optical transparency. Don't know if this is true but it is a thought. Cheers - Joe G3LLV ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] Re : Danjon Astrolabe
Hi, About transits - I like the bit in the film "Longitude" (if I remember it correctly) were Harrison's son is asked by some worthy how they get a local time check. The young lad points to the chimney on a certain house and says that they wait for a particular star to disappear behind it. Assuming that the brickwork was vertical enough and that you had good enough eyesight, it must have been possible to nail it down to the odd second; averaging over several days (long time-constant) would have made it even better. Good enough to find the West Indies anyhow. Cheers - Joe ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] EFRATOM FRK Lamp Voltage
Hi, A few years back I obtained a Racal-Dana rubidium standard with a EFRATOM FRK-L fitted. I was concerned that the indicated lamp voltage was about 5.5V where the book says it should be between 6 and 12V. Subsequently I obtained another lamp from a surplus source hoping that the voltage would move upscale when changed. Unfortunately it didn't and has stayed around 5V, slightly lower than the original. I can't put the old one back because I cracked the glass when prizing it out of the sealing compound. So, was I seen off or is this typical of the voltage spread likely to be encountered? I must say that the unit locks up quickly enough and works fine as far as I can see. I realise that the lamp voltage is only the output voltage of the first op-amp after the photo-diode and may not be a reliable indication of its true health. Anyone know of a cheap source of spare lamps? TIA - Joe ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Philips PLL
Hi, I recently used the Philips 74HCT9046A, a variant of the 4046/7046 with a charge pump on the type-II (frequency/phase) output, in a GPS frequency standard project. However this family tries to be all things to all people and I would like a simple phase comparator (EXOR will do) with said pump in an 8-pin package. Anyone know if such a beast exists, type number and source? Cheers - Joe ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] GPS SPD field
Hi, Reference a Rockwell Jupiter GPS receiver. Does anyone know if the decimal point in the NMEA $GPRMC 'SPD' ASCII field moves around? At rest it reports 0.000 but it is not obvious whether this format is maintained on the move or expands/contracts to suit. Does it keep the same precision with the most significant digits expanding or not? TIA - Joe ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] A Simple PIC Divider
Hi, While we are on the subject of PIC dividers, and if the lower order outputs (other than 10kHz) are not required, the standard divide-by-1000 part of a GPS-derived standard may easily be implemented in an 8-pin 12F629/675 saving one chip and 20 pins. My code, such as it is - Setup the required ports DIV: Set RAn to '1' Stuff here with 124 NOPs Set RAn to '0' Stuff here with 121 NOPs Goto DIV The result, a synchronous counter with a symmetrical 10kHz square-wave on RAn from a 10MHz clock input. The 245 NOPs are easily block pasted into a text editor thus saving the need to calculate the numbers for timing loops. This is so basic that I hate to mention it but someone might wish to save a bit of board space. Cheers - Joe ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
