[time-nuts] Re: HP Z3801A project update

[ed breya]

I've been doing some more cold start testing, and thought I'd share this 
info, for any Z3801A owners who may be curious about the behavior. Some 
aspects are probably well known since long ago. I've seen it all since 
first starting work on this some 10-12 years ago, so I know 
approximately what it does. Now I have been able to make some more 
convenient observations.

The setup is simply measuring the external DC input current and voltage 
while the process goes, to estimate the input power needed, roughly how 
much, and when. Only the input P is noted. The total gets used up in 
running the Z3801A, the other circuits, and conversion losses. Almost 
all the changes in power are due to the Z3801A going through its cold 
startup process. Here's a summary from a run I did this afternoon.

T=0, start, 33 W

The running supplies for everything, and the internal oven of the OCXO 
are turned on first. When the oven is approaching being warmed up 
enough, the P gradually drops to about 25 W, at about T+7 min.

It then rather suddenly jumps to somewhere around 50 W as the outer oven 
is turned on, then fairly quickly down to 45 W, then gradually declines. 
The GPS lock indicator came on at about T+10 min, not coincident with 
any particular oven condition.

The power continues to drop off very gradually (there's a lot of mass to 
heat up), until reaching nearly steady state around T+50 min, at about 25 W.

So, figure it takes about ten minutes to achieve lock (this particular 
setup), but about an hour for everything to fully warm up.

Ed