[teqc] Question about SNR mapping for AshTech stream data

Lou Estey lou at unavco.org
Tue Jun 28 17:14:51 MDT 2005


hi Henry,

> We are developing a decoder program to transfer AshTech stream data
> to RINEX file. I compared our result with the output from TEQC, I have
> a question about SNR mapping in obs files. From the AshTech document
> for the MPC message, I learned that the signal-to-noise indicator has
> a value range between 30 and 60 and the unit is dB-Hz.  But in the TEQC
> obs file head,  SNR is mapped using L1: 1 -> 1;  90 -> 5; 210 -> 9 and
> L2: 1 -> 1; 150 -> 5; 250 -> 9.  Could anyone here please explain this
> to me?

Sure.  The original SNR values in Ashtech receivers were not in dBHz
and, in fact, if you still were using a Z-12 or similar vintage or
earlier the SNRs would not be in dBHz.  Ashtech re-used the SNR spots
in their various binary formats to store SNR in dBHz starting with the
micro-Z (AFAIK), but there's no way to tell whether the SNR is the
earlier "ireg" units or dBHz unless you know what the receiver is.
The current development version of teqc will tries to figure this out,
and additionally if the receiver is determined to be a Z-12 then teqc
will convert the earlier SNR values to a dBHz equivalent.

Trimble basically did the same thing when they introduced the 4400, 4600,
4700, and 4800 receivers, switching from their original "AMU" SNR values
to dBHz, which is also what is being stored with newer Trimble receivers.
But again you don't know which is being used unless you know the receiver
type.

More on this whole topic for other manufacturers:
http://ls.unavco.org/pipermail/teqc/2004/000038.html

cheers,
--lou

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Louis H. Estey, Ph.D.              office:  [+001] 303-381-7456
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