[time-nuts] New NTBW50AA

[Bob Camp]

Hi

There is no instruction booklet for the NTBW50's and LH. The program is targeted at a TBolt. I think it's great that it happens to work at all for the NTBW50. The stuff about the filter settings has been noted by and posted by several members here on the list. I've seen it on my units here. 

Setting the elevation mask on any of these units can be done from AMU plots. The gottcha there is that multi path issues will cut in before the signal strength drops off. You want to set it a bit higher than the drop off point. Multipath can be a much larger issue than simple signal to noise. It's the path delay in multi path that's the problem. 

The sat's are all on the same frequency. However they are moving at a very high rate of speed. That creates a doppler shift in the frequency. You have to track out the doppler before you can even receive the signal. It's also why you can't use the GPS frequency directly as a reference for the GPSDO. Weather the shift is big enough to matter is indeed a matter of conjecture. Without actual filter data, there's no way to really know.

As you move the antenna around remember that keeping the GPSDO on power is the main goal. You don't have to keep it connected to an antenna as you relocate, but don't take the OCXO off power. They very much prefer to be run continuously.

Bob


 
On Sep 19, 2013, at 10:32 PM, quartz55 <quartz55 at hughes.net> wrote:

> In the Trimble NTBW50 (and Trimble made clones) you can run the auto cal via LH. The sensitivity is calculated and may appear to change. The settings can not be saved in flash / eeprom. They do not persist across multiple reboots. There is no evidence that the NTBW50 actually uses the changed settings. 
> 
> Switching elevation masks, changing AMU limits, works with both units. These changes do save to flash / eeprom on both units. They persist across multiple reboots on both. The do impact the way both units function. 
> 
> Bob, I suppose you came across this by experimentation, not by any instruction booklet?  I guess we're on our own here with the Nortel units.  How about Mark's (I think) suggestion to "set the EL mask to a low value (F E 0), clear the signal data (S A C) let the unit run for a day or so, then do the osc autotune (&A). This will set the elevation mask to a level that matches what your antenna can see.  Or you can check the elevation plot (S A E) and see where the tick mark shows the signal level dropping off and enter that value manually."
> 
> My guess is that the antenna you have is virtually identical to the Lucent 26 db gain device. I doubt that the cost of getting one is worth the money. If you want a better antenna, go for one of the $300 - $500 choke ring antennas. You will also need a bias Tee (they mostly run on 12 volts), but it's often included. 
> 
> Well, that's not going to happen, the $3-500 anyhow.  I was also thinking about the filter, aren't all the L1 sats on the same freq, so there shouldn't be any phase difference with respect to the sats, but I may be way off base here.
> 
> I found a nice 15' locust log today that's about 6-8" dia. that I can strap to one of the fence posts and get rid of the 3/4" EMT.  Wife likes it too because it looks 'rustic'.  Cool.
> 
> Thanks, Dave
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