[time-nuts] New NTBW50AA

Bob Camp lists at rtty.us
Sat Sep 14 17:38:46 UTC 2013


Hi


On Sep 14, 2013, at 12:45 PM, "quartz55" <quartz55 at hughes.net> wrote:

> Today I moved the antenna to above the beams.  This is temporary because it's in the way of the beams turning.  I guess I need to get someone out here to help me install it on top of the beam mast.  I don't feel confident to do it myself anymore.  I suppose it's not going to hurt anything if once in a while the antenna gets rotated?  Just not while I'm doing something with the Nortel.  It's pretty much in the clear and as high as I can get it.  It sees clear sky especially to the south except for one tree and the antenna is probably within 10' of that tree's height.  There are still trees to the east that I just can't do much about.  The ones to the west are about 100' away and the antenna shouldn't see them much.
> 

As long as the GPS antenna does not rotate that should be a good location. If it rotates, you will get a few inches of displacement which is less than ideal. The larger issue will be how the antenna handles lightning and the near field transmit power from the beams. 

> http://i251.photobucket.com/albums/gg287/DogTi/time/abovebeams_zpsbf8474c1.jpg
> 
> So the Osc ppt is the offset from what the Nortel thinks is exactly 10MHz as I read it on page 117 of the ThunderBolt instructions (thanks Tom).  How do I tell how accurate the Nortel thinks exactly 10MHz is, or can I assume it's right?  If right is the case, then if I get a spread of around 300ppt, that means I'm always within 300x10^-9 Hz of 10MHz or .0003Hz at 1GHz?

PPT = parts per trillion that's one in 1,000,000,000,000 (12 zeros). One Hz at 10 MHz is 0.1 PPM. PPM is 1 in 1,000,000 (six zeros). PPB is nine zeros, or one Hz at 1 GHz. It's also one nanosecond per second. 

300 ppt would be 0.3 Hz at one GHz. 

(yes, you can find a *lot*) of posts to the list where I've slipped a decimal on that stuff).



>  Or is my thinking off base and did I miss a decimal somewhere?  I suppose the ppt spread is pretty much a function of how stable the osc is once other factors like temp, antenna position, sat acquisition, etc, are optimized?  

Also include the errors in the GPS signal:

1) Uncorrected ionospheric errors
2) GPS clock errors
3) GPS almanac errors
4) Antenna location errors (including interesting trivia like tides)
5) Multi path signal errors
6) Temperature induced errors (or not) on the antenna
7) Drift / phase errors in the GPS receiver (there's lots of doppler on the signals). 
8) Just plain dumb decisions by the firmware

Since most of the GPS errors are going to "track out" they will not show up on the display. They will indeed shift your output frequency.


> That's what I infer from what Skip Withrow from RDR told me about the oscillators.  He told me they can vary by a factor of 10.

The temperature stability of those OCXO's likely is within about 2:1. Aging wise they are like any OCXO, the longer they are kept power on, the less they will drift. 

Bob

> 
> Dave
> N3DT
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