[time-nuts] KS-24361 GPSDO question

[Bob Camp]

Hi

Another one up and running !!!

> On Nov 9, 2014, at 11:08 AM, paul swed <paulswedb at gmail.com> wrote:
> 
> Hello to the group thanks for the help so far.
> The KS-24361 is running and communicating with the z3811 software.
> 
> Question 1
> I have an active antenna system so need to fake out the 24361.
> I have tried a 220 and 110 ohm R on the antenna with rf input Isolating
> capacitor to simulate the current n active antenna would draw.
> I measured the active antenna at 40 ma. so about 125 ohms will do.

I used a 110 ohm resistor on mine. Not from any calculations, it’s the first one I grabbed.
 
> The GPS LED flashes.
> When I attach a real active antenna it turns off.

The flashing GPS LED seems to be “I can’t find an antenna / no antenna current”. 

The solid on GPS LED seems to mean “I have an antenna, I’m trying to get find enough sat’s to do some good”.

> 
> Question 2
> I can see the TI/PPS is pretty noisy compared to the Z3801 the spikes go
> from + to - 4 X 10-8th. Also the EFC is steadily rising. I am pretty sure
> this was the comment about the system needs to run for 30 days so it ages
> and adjusts to operation.

I tossed up plots of frequency and time run over a day a while back. You could use that to judge what’s going on with your unit. They were taken within a few days of turn on. Total time wander was 30 ns p-p. Frequency was 7x10^-11 p-p. All data was on the 15 MHz output, not on the PPS.

The 30 days is the likely time to get things to settle in to best performance based on Z3801’s.

Are you looking at the 1 pps on the RS-422/ PPS jack or on the interface connector? 
If on the interface connector, which one are you looking at?
If on the RS-422, do you have a “decoding” issue (it’s a balanced signal)?

> Or do I actually have a questionable unit. I would want to return the unit
> if its bad. The seller seems very responsive.

I would let it run for several days before doing anything. They have been turned off for a *long* time.

> 
> Question 3
> After the survey completes at least 3 hours for me the system goes into
> position hold. I believe this is normal.

Yes, that is correct. 

> 
> Comments
> I was watching the super cap discharge. It runs the battery backup to the
> GPS receiver. I was surprised that its rate seems some what high. I would
> believe it can only hold data for a few hours.

Thus my earlier comments about it being a 1 or 2 day sort of thing. With a 3 hour survey time, that’s probably ok in a cell site. The discharge is *much* higher up around 5V(5X) than when it’s down around 2.5.

> I need to make better
> measurements and the fact is since I will be installing 2 X AAA external
> batteries it doesn't matter.

There’s plenty of room in the box. How about pasting a battery holder to one wall and keeping all the wires inside?

By today’s standards, that super capacitor really does not qualify as very super. You might replace it with a more modern / much higher C part. Less than $5 (delivered) on eBay will get you one that’s 100X larger (3 F vs 0.022 F ). 

> 
> Startup cold can be 34 or so watts. Normal warm running is 20 watts. So if
> your looking at battery backup some figures to use.

That’s a little less than I see for a pair of boxes and a bit more than I see on a single box. My pairs are running right at 30W. They are running warm.

If you watch the current as the unit starts up, it does some odd things. I started out with a supply with a fast current limit on it. It was not happy running a pair until I opened it up to almost 3A at 30V. It limited at 2A / 30V.

> 
> Reacquire for me after a short 5 minute power outage is about 10 minutes to
> get the green led and outputs.

That sounds about right as well. 

> 
> Last comment
> Seems a shame there is not a repository we could add all this good
> information to.
> I believe its going to get lost with this method.

At some point, once we get it all doped out *and* confirm what is and isn’t right, putting it all somewhere is a good idea. We are still in the “Bob made another mistake and here it is” phase of things. I have no problem with being there. It’s a normal part of doing this. I also accept that it will be a while before all of the T’s are crossed and I’s are dotted. Logging this all to a web site with every zig and zag described might make fun reading. It’s not going to help somebody get one running a year or two from now. 

One major unknown at this point is how big a supply there is. These have not been a very common item up to this point. They may vanish and never re-surface after this guy sells a couple dozen. There also might be 10,000 of them in a warehouse in Atlanta, all headed to auction next week. Who knows. If there are a whole bunch more, then we very much do need to get this moved somewhere we can refer people to once it’s all figured out. There are multiple sites that I’m sure would be happy to store a consolidated page (or ten) of information. 

Bob

> 
> Regards
> Paul
> WB8TSL
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