[NLRS] Efratom Lpro101 Rubidium Standard

[tosca005 at umn.edu]

Thanks to everyone who replied.

It seems that the consensus is that in spite of KA7OEI's recommendation 
that the aluminum box alone is a sufficient heat spreader/heat sink, the 
addition of an additional heat sink is a good idea. Just to play it safe, I 
already picked up a couple of aluminum heat sinks from eBay, and will plan 
to use one on the project (and have a second as a spare, since it was 
pretty slow arriving from China!). It is nicely matched to the size of 
either the lid or the bottom outside of the aluminum box I am using.

Doug, N0NAS: Yes, that was the web article I was referring to. I am still 
undecided about mounting the Lpro101 to the inside of the lid vs. the 
inside of the bottom of the box, but if the latter, I think I can grind off 
the worst imperfections with a Dremel tool. My box is not ribbed inside, 
just has some mold marks and perhaps a slight curved departure from true 
flatness. Your reminder about adding more filtering to the power supply is 
appreciated. I think that the capacitors and inductors of KA7OEI's design 
should do the trick.

Chris, N0JCF: Thanks enormously for the tip on the thermal gap filler pads. 
This sounds like just the thing to make the heat transfer more reliable 
without resorting to a visit to a machine shop.

Ron, K5LLL: I plan to use a pre-built boost regulator (from China via eBay) 
to raise the supply voltage from 13.8 to a valid operating level. So there 
will likely be at least a little extra heat from that. I think that the 
KA7OEI recommendation to only boost the voltage to the "minimum 
specification" level of 19 vdc instead of the "typical specification" value 
of 24 vdc makes good sense to minimize battery drain and heat production. 
But once the project is built, I will see how hot it gets, and as you 
suggested, adding fan(s) to the heat sink could be an easy upgrade if 
needed. And as I mentioned, Doug's admonition to provide good filtering is 
going to be taken seriously also to keep noise out of the 10 MHz output.

Ben, NO5K: Sorry I forgot your name and callsign from the RMG meeting. This 
old brain of mine seems to leak like a sieve but practice should make 
better, if not "perfect". I also guess I mis-understood our ultra-brief 
conversation about which rubidium standard you are actually using, i.e. the 
FEI 5680A, not the Efratom Lpro 101. But I am sure that the same principles 
apply.

Jim, K0MHC: I remember our prior discussion of how you use the OCXO for 
routine roving after re-checking it against the more accurate rubidium 
standard, and the benefits of using the OCXO out in the field. Thanks for 
confirming that I was not going crazy -- my recollection was that the OCXO 
needed to be put in an INSULATED container to keep the heat in, vs. the Rb 
standard which needs to GET RID of excess heat. I was a bit fuzzy on that 
before, but it is clear now. I have an enormous number of projects to work 
on, and even since retiring from my (often) 80 hour/week job (only paid for 
40/week, unfortunately!), I still don't find myself twiddling my thumbs 
wondering how to keep busy. :) One of the other projects in my pipeline is 
a GPS-disciplined OCXO. I believe I have all the parts for that project 
except a PC board for the GPS module (so I will build it up on a piece of 
perfboard) and a GPS antenna (readily available, just have not picked one 
up yet). KA7OEI seems to dismiss the possibility of using the GPS 
disciplined OCXO for roving, unless you are operating mainly "stop and 
shoot" mode with ample time to re-gain GPS lock after moving to a new grid. 
This sounds overly pessimistic to me, since my experience with a good GPS 
unit is that it can easily keep and/or quickly re-acquire a lock during a 
grid-to-grid move under normal circumstances without a dense tree cover. 
(And who wants to operate a rover while parked inside a dense forest???) I 
guess if I get both projects built I can tell instead of guessing. Oh yeah, 
I was delayed in building that project because I thought to myself, 
"wouldn't it be neat if I added an LCD to display the Maidenhead Grid 
Square and other info like time, velocity, elevation, lat/lon, etc. right 
from the GPS that was being used primarily for its 1 PPS signal?" Oh how 
true that trying to make it "perfect" can prevent it from getting made at 
all! :( Sometimes, "good enough" is the only way to make it happen!

Once again, my thanks to all of you.
73 de W0JT/5, John P. Toscano