In a message dated 24/01/2014 21:48:27 GMT Standard Time, ail...@t-online.de writes:
New ways of RF design - see photo ;-) ------------- Definitely the last word in high rise developments:-) And glad to hear you got it sorted. ---------------- Ok, I put three 1N4148 in series between DAC out and EFC in and a pull up of 4k7 up to 12V. It shifts the DAC voltage 1.8 volts up, so the osc is able to tune to 10MHz+3Hz. Locked! Now I can go back to the sofa, having a beer or two, being sweet again to my wife and my dog, :-) Thanks Volker Am 24.01.2014 17:49, schrieb Volker Esper: > Thanks so much, Nigel, for this very interesting mail. > > Yes, the voltages are exactly as my ones. And yes, I've removed the > oscillator, already. I then removed the thermal isolation from the osc, > as well as the label, in slight hope for a hidden tuning screw. Of > course, there isn't any. > > I, too, had this idea to level shift the EFC voltage. So I took seat at > my computer to find out, which maximum EFC voltage would be ok. And saw > your mail. Do you have any further information about the osc? The number > on the sign (Trimble *0110-2450-T* *34310-T*) isn't really informative. > By the way: When removing the big Trimble label I found a smaller one > beneath, reading "DOC2127 0101/1940"; I think it's a Tekelc osc? > > Is there a pull-up resistor behind the EFC input pin so that I could use > two diodes for level shifting? Or how did you? > > This part is more thrilling than I expected... > > Regards > > Volker > > > Am 24.01.2014 12:08, schrieb gandal...@aol.com: >> Hi Volker >> >> One possibility, as I found with one of these recently, is that your >> oscillator has aged such that the required EFC voltage for 10MHz output is now >> outside the range provided by the board. >> >> The EFC behaviour can be tracked if Lady Heather is enabled from switch on >> and the DAC voltage monitored. >> >> The EFC voltage should start at 3 volts, in my case reported by LH as >> 3.000002 Volts, and will sit at this level until enough satellites are being >> tracked for the board to decide it can start the conditioning process, at >> which point the DAC voltage will ramp upwards over the course of a few seconds >> until the point is reached where the oscillator frequency crosses 10MHz and >> the control loop takes over. >> >> All standard stuff of course but, as you've discovered, if the oscillator >> hasn't reached 10MHz by the time the EFC voltage reaches, in my case >> anyway, approximately 5.6 volts the board's "OSC" report switches to "BAD" and >> "Normal OSC age" switches to "OSC age alarm" and LH highlights both in red. >> The EFC voltage finishes its ramp at 6 Volts, reported as 6.000004 Volts, >> and then just sits there, all exactly as you're seeing. >> >> Having removed my "faulty" oscillator, something that needs to be done >> VERY carefully to avoid damage to the board, I found that it required an EFC >> voltage of just under 6.6 Volts for the the output frequency to reach 10MHz. >> >> The seller, fluke.l, was very helpful as always and offered to supply a >> replacement 34310-T oscillator, this one did have it's required EFC voltage >> in the correct range and resolved the problem. >> >> However, whilst waiting for the replacement to arrive I left the original >> oscillator on test and monitoring it for a while suggested that the only >> thing "wrong" with it was the required EFC voltage, so I reconnected it to >> the board using a wired lash-up on the bench with a simple 2 Volt level >> shifter inserted into the control loop and did indeed get a locked condition >> with Lady H reporting the DAC voltage from the board as close to 4.5 volts. >> >> This suggests that whilst the board design requires the oscillator EFC >> Voltage at 10 MHz to be between 3 and 6 Volts an oscillator that falls outside >> this range shouldn't automaticall be assumed to be "faulty" in more >> general terms, although it's obviously getting a bit long in the tooth and that >> doesn't help much if it happens to be soldered into your circuit board ! >> >> Whilst it is possible to remove and replace the original oscillator there >> is an alternative to physical replacement, one which I've now implemented, >> and this uses the mounting positions already available beneath the >> oscillator, not usable though until it's removed, to fit a couple of SMA or SMB >> connectors. >> These two connectors couple the 10MHz signal from the oscillator into the >> board (J9) and the EFC Voltage out to the oscillator (J10). >> Although there is a regulated supply available from the oscillator, which >> might be expected to supply the EFC circuitry, in practice this connection >> does not seem to be required. >> I have not investigated further as yet to determine whether the board auto >> senses and uses this supply if it is present, or whether it always just >> ignores it, but it doesn't seem to be an issue either way and it's interesting >> to note, at the extremes anyway, that LH does report the DAC voltage to be >> the same in both instances. >> The oscillator can be powered from the board or given its own supply, in >> which case the only required connections between them are the two coax leads. >> >> Using this arrangement, and some variation of a positive or negative level >> shifter if required, it becomes possible to use different oscillators with >> the Nortel board and it does become an even more interesting toy. >> >> One limitation though when using the Nortel boards in this way is that >> they don't seem to share the versatility of the Thunderbolt when it comes to >> modifying the oscillator conditioning parameters. >> It's suggested in the LH documentation that such commands are currently >> "undocumented" but that also leaves the possibility that any such change >> might only be a firmware option. >> If anyone has further information on this that would be much appreciated. >> >> I've been sufficiently impressed with the modified unit that I'm seriously >> considering modifying another one, even though it doesn't actually "need" >> it, although not over enthusiastic about repeating the oscillator removal. >> However, an added bonus with this configuration is that it's also more >> forgiving when it comes to any damage caused during removal of the original >> oscillator, since the pads for the external connectors are separate from the >> internal oscillator pads. Obviously it needs to be ensured that any >> necessary continuity is maintained but that could be easier if a board mounted >> oscillator is no longer required. >> >> The later single board unit, the NTBW50AA, has a similar external connector >> arrangement but in this case the connector pads are available without >> removing the original oscillator. >> This hints at the possibility that perhaps a simple track interruption >> might allow fitting of an external oscillator with the original still onboard >> but examination suggests that the onboard connections route first to the >> internal oscillator so that would probably still need to be removed. >> >> Regards >> >> Nigel >> GM8PZR >> >> >> >> >> >> In a message dated 23/01/2014 23:59:34 GMT Standard Time, >> ail...@t-online.de writes: >> >> Hi! >> >> I bought a Trimble/Nortel GPSDO >> >> http://www.ebay.de/itm/300933951405?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m >> 1497.l2648 >> >> and Lady Heather's now tells me that everything is alright - except >> - DAC 6.000004V >> - OSC BAD >> - osc age alarm >> >> The rectangle "10MHz" output signal (J5) shows a signal at about 9.8MHz >> (a deviation of about 200kHz), wobbling 4Hz up and down. Oddly enough, >> the direct oscillator output (J4) shows a sine wave at a stable >> 10.0000004MHz (a deviation of 0.4Hz). >> >> It seems to me it's not the oscillator that is bad but the servo loop - >> what can I do? >> >> Thank you >> >> Volker >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > _______________________________________________ > 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.