[time-nuts] Rb video

Bob Camp lists at rtty.us
Thu Aug 8 22:05:17 UTC 2013


Hi

Bigger is indeed better when it comes to heat sinking these Rb's. Unlike an OCXO, they run quite a bit longer if you cool them well. If you want to get fancy, you can run a speed controlled fan on the heat sink to regulate the temperature. You still want to pick a temp that's as low as you can practically get it for your control point. 

I've fried a *lot* of Rb's over the years…..

Bob


On Aug 8, 2013, at 7:08 AM, Dr. David Kirkby <drkirkby at gmail.com> wrote:

> On 6 August 2013 09:37, Raj <vu2zap at gmail.com> wrote:
>> Found this on Hack-a-day
>> 
>> http://www.youtube.com/watch?v=chrzrod3tQY
>> 
>> Cheers
>> 
>> --
>> Raj, VU2ZAP
> 
> Interesting video. I decided to but one of the distribution amps. I
> already have the rubidium. There were a few things that struck me in
> the video.
> 
> 1) Having a PIC to control an LED seems a bit OTT. Personally I'd just
> stick a second LED - one as a power indicator, the other as a lock
> indicator, rather than make it flash when warming up, and solid when
> locked.
> 
> 2) If one does have a flashing LED, it would be better if it is
> slower, in case there are any epilepitcs about. As someone who suffers
> from photosensitive epilepsy, I would not want it flashing any faster
> than 1 Hz. He should just about be ok, but I'd feel a bit happier if
> it was slower.
> 
> 3) I'm not really convinced there is a need to change the output
> impedance from 75 to 50 Ohms. The impedance mis-match is pretty small.
> 
> 4) More concerning to me would be the fact the output connectors are
> 75 Ohm, and so would be damaged with the larger male pin of a 50 Ohm
> connector. I guess one might get away with it given one is not going
> to be disconnecting this a lot, but I think I'd buy 75 Ohm BNC plugs
> to put on one end of the cable, and 50 Ohm BNC plugs on the other end,
> sticking a bit of heatshrink on the 75 Ohm end of the cable so I know
> they are not standard BNC cables.
> 
> 5) I wondered if there is enough cooling air there? What size heatsink
> would be optimal? I think unlike most electronics, one does not want
> to cool the rubidiums too much, so "bigger is better" might not apply
> here.
> 
> 6) Is the use of a SMPS a good idea? I thought the Rb oscillators
> should be powered from a linear supply. I don;t suppose it is possible
> to get a linear power supply in there.
> 
> 7) He scrapped the BNCs configured as digital lines. I would have
> thought it worthwhile bringing out a 1 pps output, which I think those
> Rb oscillators have.
> 
> 8) I wonder if one could fit a GPS locking module in that box and
> antenna connector on the box.
> 
> 9) It will look very odd to have the heatsink as the front panel !!
> But I guess that is a small price to pay for getting a reasonably
> sized box and
> 
> 10) I suspect the box will be hard to keep in place, since with a
> dozen or so BNCs on the rear, that is going to go where the cables
> tell it to go, rather than the other way around. Perhaps a heavy
> heatsink will mittigate that.
> 
> 11) If I recall correctly, there is a way of adjusting the freqency of
> those rubidiums, though I guess for the intended application, a Rb is
> plenty good enough. I know it is for me, but perhaps not for a
> dedicated time-nut.
> 
> Dave, G8WRB
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