[time-nuts] LPRO101 orientation vs lock

k6rtm at comcast.net k6rtm at comcast.net
Thu Sep 16 15:07:19 UTC 2010

I assume you mean Tektronix TM5xx or 5xxx modules. 

I haven't seen an LPRO plugin, but considered doing one for my TM506 rack. My conclusion was that I couldn't get rid of enough heat without cutting custom fins for the LPRO. 

Recall that the physics package in the LPRO is the biggest source of heat, and looking at the unit with the connector facing you and on the left, the physics package is along the right side toward the rear of the unit. I decided the way to mount the LPRO if I had to go vertical was with the physics package closest to the top, to minimize the components that got baked. (I welcome recalibration of this opinion from more knowledgeable sources!) 

If I could cut fins for the new "top" edge, as well as a good plate for the bottom, and some fans, i might be able to get rid of enough heat to make it work. I considered mounting the LPRO to the rear of the module connectors, in the area containing the linear power supply components. 

I reconsidered on recalling admonishments in the LPRO docs and on this list that cesiums do not like magnetic fields! Mounting the unit next to large power transformers wouldn't seem to be suck a good idea... 

You might have better luck running it in a TM5006 rack, as they have much better cooling and airflow (a reason to get rid of that 506 and pick up a 5006!). 

I've had good results with my LPRO mounted on a half inch plate of T6061 aluminum and an old AMD heatsink+fan mounted above the physics package, held in place with arctic silver heat transfer compound and spring-loaded wire clips going to the plate. I've been meaning to run noise studies to see if the fan causes any problems (vis a vis mag fields). 

Since I expect to be using the LPRO only occasionally, I've been trying to talk my son into making me a steampunk-themed case, something like rosewood with brass corners and detailing... 

Cheers and 73 -- Bob K6RTM in sunny silicon valley 

On Sep 16, 2010, at 2:51 AM, d.seiter at comcast.net wrote: 

> I got one of the ebay LPRO-101s about 6 months ago and played with it for a while, but had problems maintaining a lock. First of all, it has a heat sink bolted to the bottom that is just a little larger than the LPRO itself, including being about 1.25" thick( 1" fins). Typical frequency when locked is 10,000,000.007 on a 5360A clocked by a Z3801A. 
> Both then and now, it takes about 45 seconds to lock from cold, and will stay locked for about 45 minutes. I found that in the position with the heat sink on the bottom will stay locked the longest (up to a few days), but then it becomes intermittent. Other positions will lock for a while, but bottom down always works the longest. 
> For those of you who employed these in TM5xx or similar plugins, did you have lock issues? Is my unit just old? 
> Dave 
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