[time-nuts] Rb video

[Dr. David Kirkby]

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