[time-nuts] Re: Turning off display on HP 58503 A or B
Lon, K5JV said: > Comments from anyone who has actually seen inside one of these ovens would be > appreciated. http://www.realhamradio.com/GPS-oven-journey.htm -- For lots of info on the Z3801A start here: http://www.realhamradio.com/GPS_Frequency_Standard.htm (Time sink warning.) -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Noise down-converter project
I've been working on final design cleanup, mainly in the RF. I found quite a bit of spurious LO harmonic content up to almost 2 GHz, with some quite strong (-75 dBm). It was time to clean up the experimental wiring layout, so I simplified the cabling and consolidated the RF stuff onto the LPF board. This improved things a bit, but some spurs were still pretty big. I presumed most of it was going right through or around the LPF, and some due to common-mode and cavity resonances inside the box, which can have many modes. I added a small LPF about 300 MHz (10 pF/50 nH/10 pF), inside its own tiny shield box, forming the last bastion of filtering, right at the inlet of the pigtail cable that goes to the isolated SMA bulkhead fitting, and including another CM choke (only 1 pass of cable). This filter is high enough up (over ten times the fc of the main LPF) that they shouldn't interact very much - they are isolated only by the 3 dB pad in between. All along, I've wondered what to do about the reflected power from the main LPF, that mostly has to go back to the mixer. They are separated by maybe 300 pSec of cable, which could be in the range for resonances at the upper end. But, various experiments during development, including padding the LPF input, and even making a diplexer with a 50 MHz HPF to take the HF content into a terminator, showed no difference in the noise output flatness, although the spurious levels likely would have changed a little - some up, some down. So, I decided to keep it simple and just let 'er rip, with nothing extra at the LPF input. Things are now at levels where the fine (and subtle) details show, mostly cable dress, and grounding. I'll probably be adding bits of shielding here and there, and maybe fooling with some RF absorbing foam to see if any box resonances are a problem. Speaking of subtle effects, here's something interesting. The little shield box for the 300 MHz LPF is a type with a fold-down lid, on a hinge formed by thinning the sheet steel. It's only good for a few open and close operations before the hinge breaks apart, so I kept it open while building and testing the filter. It looked great, and the time came to close everything up and look at the spurs again. I closed the lid, and bent the retainer tangs a little, for good closure. Virtually all the higher frequency spurs got a few dB worse. So, was it that the lid isn't really grounded thoroughly, and acting as an antenna to bypass the filter, or did it affect the choke Q or part values enough, or is it that I also changed the cable dress a bit while putting it all back together? I'll have to figure it out. Anyway, it's looking pretty good right now. With everything closed up, including the box lids, as it would be when completed, all the spurs show around -90 dBm or less. There were maybe two dozen noticeable spurs identified earlier. Some are now in the noise floor (around -105 dBm, but some remain, sticking out. I think most will disappear if I figure out that 300 MHz filter box lid, which would leave the 70 MHz as the main offender. This isn't surprising, since it's the biggest signal of all, and it's not filtered all that much - it's too close to the main LPF fc, and below the 300 MHz LPF. I should be able to knock it down enough with detail work mentioned above, and I'm also pondering ways to make a 70 MHz trap, if it won't go away. I have a couple of 70 MHz crystals, so I could try this kind fairly easily. Does anyone have any handy design info for crystal notch filters in this frequency range? For an LC trap, it looks like a single L and C would be enough to get the job done, without interacting too much with the other filters. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Turning off display on HP 58503 A or B
Hi Lon, hello to all members. In 1995 the art of temperature control was a good bit more advanced, and a bi-metal thermostat would not be stable enough These ovens have a semiconductor temperature control; so I would suspect a shorted transistor. These failures in OCXO are not that rare, and that is why there are thermal safety fuses. And please don't defeat them ! 73 from Claude VA2 HDD Le 02/06/2022 13:55, K5jv via time-nuts a écrit : CAUTION: This email originated from outside your organization. Exercise caution when opening attachments or on clicking links from unknown senders. I was recently evolved in a discussion about the HP 58503 option 001 display. The general idea is that there is some command to tune the display on or off. A few ideas were offered but no one had anything except "they heard about it." I have found nothing on the subject from old HP literature. Comments would be appreciated. I am not talking about turning the power off to the DC/DC converter. On a different subject: A couple of month back I got some strong criticism about suggesting that the oven in the Z3801A was a potential source of problems. I just got another Z3801A in for repair. Same symptoms as before; appears to turn on normally but after a while goes into holdover and stay there, same LH flat lines. Once again the problem turned out to be the oven. It was unusually hot to the touch. Changing the oven solved the problem. Now my question. I have never opened one of these oven, so have no real idea exactly what is inside. I would suspect that one of the oven's thermostats is stuck in the "on" position. Since it is a "double oven", there could be two thermostats? If these are mechanical contacts, as one might expect fro the 1995 era, can they be cleaned or replaced? Comments from anyone who has actually seen inside one of these ovens would be appreciated. 73 de Lon, K5JV 281-795-1335 [a96323c7-47c0-46b2-8018-f039618476d5] ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Turning off display on HP 58503 A or B
Hi Both control loops in the 3801 OCXO’s are thermistor based. If the outside loop goes nuts, the device might survive. If the inside loop shorts out, the normal result is a melt down of the OCXO innards. Bob > On Jun 2, 2022, at 9:55 AM, K5jv via time-nuts > wrote: > > I was recently evolved in a discussion about the HP 58503 option 001 display. > The general idea is that there is some command to tune the display on or > off. A few ideas were offered but no one had anything except "they heard > about it." I have found nothing on the subject from old HP literature. > Comments would be appreciated. I am not talking about turning the power off > to the DC/DC converter. > > On a different subject: A couple of month back I got some strong criticism > about suggesting that the oven in the Z3801A was a potential source of > problems. I just got another Z3801A in for repair. Same symptoms as > before; appears to turn on normally but after a while goes into holdover and > stay there, same LH flat lines. Once again the problem turned out to be the > oven. It was unusually hot to the touch. Changing the oven solved the > problem. Now my question. I have never opened one of these oven, so have no > real idea exactly what is inside. I would suspect that one of the oven's > thermostats is stuck in the "on" position. Since it is a "double oven", > there could be two thermostats? If these are mechanical contacts, as one > might expect fro the 1995 era, can they be cleaned or replaced? Comments > from anyone who has actually seen inside one of these ovens would be > appreciated. > > > 73 de Lon, K5JV > 281-795-1335 > > > [a96323c7-47c0-46b2-8018-f039618476d5] > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Turning off display on HP 58503 A or B
I was recently evolved in a discussion about the HP 58503 option 001 display. The general idea is that there is some command to tune the display on or off. A few ideas were offered but no one had anything except "they heard about it." I have found nothing on the subject from old HP literature. Comments would be appreciated. I am not talking about turning the power off to the DC/DC converter. On a different subject: A couple of month back I got some strong criticism about suggesting that the oven in the Z3801A was a potential source of problems. I just got another Z3801A in for repair. Same symptoms as before; appears to turn on normally but after a while goes into holdover and stay there, same LH flat lines. Once again the problem turned out to be the oven. It was unusually hot to the touch. Changing the oven solved the problem. Now my question. I have never opened one of these oven, so have no real idea exactly what is inside. I would suspect that one of the oven's thermostats is stuck in the "on" position. Since it is a "double oven", there could be two thermostats? If these are mechanical contacts, as one might expect fro the 1995 era, can they be cleaned or replaced? Comments from anyone who has actually seen inside one of these ovens would be appreciated. 73 de Lon, K5JV 281-795-1335 [a96323c7-47c0-46b2-8018-f039618476d5] ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
