Hi > On Oct 20, 2020, at 10:45 AM, Luiz Alberto Saba <[email protected]> wrote: > > Hi Bob > > In a previous tread, someone said that cooling PRS-10 will only make the unit > consume more energy, since it has to maintain the lamp hot. > Is this wrong?
You need to read the entire thread. Cooling a Telecom Rb to a reasonable temperature *is* a good idea. The parts that are not attached to the oven assembly live *much* longer at a lower temperature. Most of these small Rb’s die when this or that weird part on this or that board dies. Caps are usually the first to go, but they can be tracked down and replaced. If it’s a solid state part with no known replacement source …. the unit is dead. Also complicating the repair process is the total lack of any alignment / setup information on these Rb’s. If the part you replace requires realignment ….. you are flying blind. Bob > Before I read the previous tread, I was thinking of electronic thermostat/fan > but... > > Em 20/10/2020 10:34, Bob kb8tq escreveu: >> Hi >> >> Not very well organized message here …. I’m still working on my first cup of >> coffee …:) >> >> First up: What do I do? >> >> My “lab” is in the basement of our house. There is HVAC running pretty much >> year round. The temperature “wanders” between about 20 and 25 C over a >> year. It cycles about 2 or 3 C at roughly a 1 to 2 hour rate. I have three >> 5065 >> Rb’s running full time on a rack. I have a couple of GPSDO’s running on >> another >> rack. Various OCXO’s get tested on a bench. All of it is “out in the open”. >> >> I have looked into various approaches to temperature control ( thermo >> electric >> heaters ….). I have a big pile of water pumps, TEC’s, piping, and radiators >> siting in a dark corner of the room. The more I looked into the power >> required >> to do that, the less I liked the idea …. >> >> I do have a few cardboard boxes and a small pile of “beach towels” that I >> use. >> If the measurement is particularly sensitive, I put a towel over the test >> set. If >> the device is large, I put a box over it. That generally works quite well to >> reduce >> fast changing temperature from drafts in the room. >> >> ====== >> >> Are you trying to lock the PRS-10 to the UCCM? If so, don’t bother, the net >> result is a PRS-10 that is not very stable. Just use the UCCM’s output. >> >> Practically speaking, the PRS-10 is a 0-50C device. It’s no different than >> other >> Rb’s in that respect. It also is no different than the rest in making those >> limits >> really hard to pull out of the data sheet. They talk about 65C baseplate, but >> that’s not ambient. >> >> The UCCM has an OCXO in it that is (probably) rated too 70C. It depends a >> bit on what version / vendor you happen to have. In still air the OCXO is ok >> to 50, in moving air, it should be all right at 70. No idea how the rest of >> the parts >> on the board will do above 50C / moving air. ( = I’d bet there will be >> problems >> above 50C). >> >> The PRS-10 needs a heatsink on it or it will quickly die. It will live a >> longer life >> with a better / bigger heatsink. With a small one, figure 2 years. With a >> fan or >> something large, figure > 5 years of life. That’s all in a indoor situation >> with a >> HVAC system keeping the ambient around 20 to 25C. The small heatsink >> gets around 50, the bigger one + fan may get down to 40C. >> >> The real issue with both the PRS-10 and the UCCM is to reduce the >> temperature >> swings. The UCCM will track out long term changes. You just need to protect >> it >> from quick changes. Depending on which PRS-10 you have the temperature >> performance >> may be better or worse (per the specifications on the part). A wooden box >> with >> heaters / fans can do this, there are other ways. >> >> A lot depends on just how crazy it gets where you are in Brazil does it get >> above >> 40C? ( I looked it up, the record is 44.7C …. yikes … ). Ideally you want to >> keep >> the heatsink around 40C. That’s not going to happen if it’s 40 out. Running >> the >> part at 55 C all the time is not a good idea. >> >> More or less, you normally need 10C of “headroom” on any sort of heated >> device >> (like a heated wooden box). You also have a practical problem coming up with >> a heatsink that gets to < 10C relative to ambient. The net is that your >> heatsink >> is at “max ambient” + 20C. For a somewhat more practical heatsink, the >> numbers >> are worse …. sorry about that. >> >> What’s a “big” heatsink? Think of something the size of the Rb with a high >> speed >> fan attached. As noted in various posts the magnetic field from the fan will >> not >> make the Rb happy, some sort of ducting to keep it a bit further away might >> be >> a good idea. That sort of thing probably *does* get you within 10C of >> ambient . >> >> The bottom line is that this sort of gear normally gets used in a location >> that has >> heating / cooling. Temperature may swing from 10 to 30, but that’s about it. >> They >> generally have pretty big fans moving air around. A cell phone “base >> station” is >> one example of this sort of setup. >> >> Probably enough for now….. >> >> Bob >> >> >>> On Oct 20, 2020, at 7:36 AM, Luiz Alberto Saba <[email protected]> wrote: >>> >>> Hi Bob >>> >>> I will try with the toroid setup (as soon as I receive the transformer) and >>> see what happens. >>> I'm really lost in respect of thermal insulation (or cooling). >>> I'll use a PRS-10 and a Samsung UCCM gpsdo. >>> A single mass of copper (or alluminium) wil be effective for PRS-10? >>> I saw in an old trend here people saying that forced cooling is not good >>> for the PRS-10. >>> Closed box or ventilation holes? >>> It will operate at ambient temperature, in Brazil... >>> If you or someone has some hints about what to do in this respect, I'll be >>> very grateful. >>> >>> Thanks >>> >>> Luiz Alberto Saba >>> >>> >>> Em 19/10/2020 17:35, Bob kb8tq escreveu: >>>> Hi >>>> >>>> One weird issue with big caps in a linear supply: >>>> >>>> As you increase the size of the caps on the bridge rectifier, the ripple >>>> voltage goes down. The ripple *current* goes up. In some cases (say ripple >>>> voltage at 1%) it can go up by 10X to 100X of the minimum value. >>>> >>>> Why does this matter? >>>> >>>> Magnetically coupled signals and current bounce in the ground are both very >>>> real effects. They can be tough to get rid of …. >>>> >>>> There is no one solution to any of this …. :( >>>> >>>> Bob >>>> >>>>> On Oct 19, 2020, at 12:41 PM, Luiz Alberto Saba <[email protected]> >>>>> wrote: >>>>> >>>>> Hi Bob >>>>> >>>>> The phase noise is not particularly important in my case. >>>>> It will be used mainly to calibrate ocxo/rb. >>>>> I'm pendig to a good toroid/bridge/huge caps and something like LT-1083. >>>>> >>>>> Em 19/10/2020 12:38, Bob kb8tq escreveu: >>>>>> Hi >>>>>> >>>>>> What will the output of the box be used for? If low phase noise is an >>>>>> objective, >>>>>> then one needs to be pretty careful about power supply noise. If low >>>>>> phase noise >>>>>> is not a “need” in this case, then (good) switchers can be used for >>>>>> everything. >>>>>> >>>>>> What’s a “good” switcher? You want one that is reliable ( = does not >>>>>> catch fire >>>>>> on a regular basis). You also want to get the noise down into the 10 mv >>>>>> p-p range. >>>>>> That generally means filtering the output a bit. Past that the usual >>>>>> requirements >>>>>> of line / load regulation and efficiency come into play. >>>>>> >>>>>> Bob >>>>>> >>>>>>> On Oct 19, 2020, at 10:24 AM, Luiz Alberto Saba <[email protected]> >>>>>>> wrote: >>>>>>> >>>>>>> Hi guys >>>>>>> >>>>>>> Planning to build my "reference box" with a rubidium & a gpsdo. >>>>>>> SMPS will do a good job or the transformer+bridge+capacitor+regulator >>>>>>> is best suited for this application? >>>>>>> In the "test phase" I've used a switched ps for the rubidium and a >>>>>>> conventional for the gpsdo. >>>>>>> >>>>>>> Thanks >>>>>>> >>>>>>> Luiz Alberto Saba >>>>>>> >>>>>>> _______________________________________________ >>>>>>> time-nuts mailing list -- [email protected] >>>>>>> To unsubscribe, go to >>>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>>> and follow the instructions there. >>>>>> _______________________________________________ >>>>>> time-nuts mailing list -- [email protected] >>>>>> To unsubscribe, go to >>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>>> and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
