[time-nuts] Comparison of Ashtech Z-12 and Z-Sensor for timing

Magnus Danielson magnus at rubidium.dyndns.org
Sun Oct 4 23:09:42 UTC 2009


Mark Sims wrote:
> As I understand it,  the Z-Sensor is basically a Z-12 without the front panel.  The design uses more modern ICs, etc.

By the looks of things, I agree.

> Most of the Z-12s have sold from $1000-$1400.  Best to get one with a good L1/L2 antenna...  those will set you back several hundred doallars.  I have seen Z-sensors offered without antennas for $1000,  with no takers.
> 
> 
> All the Z-12s have a 1PPS output.   I don't know how well it performs or if it takes full advantage of L1/L2 signals and carrier phase processing.    

They use the signal they have. If they have L1&L2 carrier solutions, it 
will use that for the PPS. They are very good for that purpose.

> There was a Z12 manufacturing option to allow an external frequency standard input.
> It could accommodate any freq up to 20MHz in 10KHz steps.

The hardware is there, it's a software option really. The hardware is a 
input conditioner, programable divider and then a PLL to lock up the 
internal 20 MHz oscillator.

There is then various advanced options to this, which among other things 
involved cutting through so that instead of locking up the 20 MHz 
oscillator, the freq input replaces the 20 MHz oscillator completely. 
The gain is that you remove the temperature-sensitivity of the PLL lockup.

Another advanced option is to allow the "camera input" to act as PPS 
input to steer the time of the receiver. Essentially this makes the PPS 
ticks the base for sampling the channel state. Again, this is mostly a 
software option I guess.

I have not compared a normal Z12 with one having any improve stability.
I would love to do that, but it takes that someone kindly borrows me one 
and allows me to disassemble it (carefully!) to have a propper look.

The Z-sensor also has an external frequency offset.

> There are some timing receivers out there that do carrier phase based timing...  very hard to find and big bucks when you do.

The Z-12 does code and carrier phase on L1 C/A, L1 P and L2 P. That is 
what makes them so great. There are L1 C/A only receivers that also do 
carrier phase. Some only do that if they have a software option.

Cheers,
Magnus




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