[GPS_Standard] Dave's OCXO

[Bob Bownes]

Dick,

The problem ocxo is mine. :)

I'm also guessing the oven has an issue, either the heater isn't
heating enough or there is some other problem going on. I can
definitely link the frequency swings to temperature instability at
this point. I'm probably going to try several experiments/solutions
over the weekend starting with measuring the current drawn by the
oven, moving the instrument to a more stable temperature room,
increasing the insulation around the oven and modifying the
ventilation of the case itself. Lastly I'll try a new oven, but that's
going to mean getting it out of one of the other instruments or,
preferably, just modifying the instrument to allow external adjustment
of it's oven, which is a whole 'nuther class of project.

I further suspect that the 1pps could be improved by using a better
GPS, but that isn't enough change to be causing this problem.

At this point, I'll settle for getting an instrument that doesn't have
to swing from rail to rail over the course of a day trying to keep the
ocxo in line, but can't because the max slew rate is 530 hours to get
from one rail to the other.


On Thu, May 27, 2010 at 1:48 PM, Dick Moore <richiem at hughes.net> wrote:
> The thread is getting long, so I'd like to make some comments without preamble. Bert suggested that the OCXO is likely defective. I concur.
>
> I have used several different OCXOs in this project -- an HP 10811-xxxx, a knock-off of the 10811 by Cinox, and currently an Isotemp. The 10811 was very erratic as was the Cinox -- both simply refused to stabilize for more than an hour or so, at best. Both exhibited frequency "jumping" and large drift swings. Someday, I may try to reset the oven curve on both units, but it's a tedious job, and I suspect that both have other problems.
>
> I bought the Isotemp on eBay from l.fluke in China, and it works very, very well. Best, it cost me about $35 delivered. Seems to me that with the relatively wide availability of suitable OCXOs, it would make sense to try another unit, and it's always good to have a spare or two....
>
> As to switching supplies, I tried one that was so noisy it interfered with radio, TV, and wireless phones for hundreds of feet around. Then I picked up a Condor supply that puts out +24V and other .levels. It is very quiet and is perfect for supplying the 78xx regulators that follow. I've been using it 24-7 for several years without incident, and it has no effect of any kind on any of the other high-to-very-high-precision gear that's in the shop. So, quality matters more than type, I think.
>
> Dick Moore
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