[time-nuts] AMU vs dBc

Arnold Tibus Arnold.Tibus at gmx.de
Mon Nov 23 23:33:52 UTC 2009


Hi everybody,

in a document from Trimble 
(TTM637VME/TTM357VXI
GPS Satellite Receiver
Addendum, User's Guide)
I found:

"The signal level (Byte 5) is a linear approximation of C/N0 which is stated in antenna amplitude
measurement units (AMUs), a Trimble devised unit. An approximate correlation of AMU
levels to C/N0 follows:
5 AMUs -20 dB SNR
16 AMUs -10 dB SNR or AMUs 51 *
26 AMUs -5 dB SNR

The C/N0 is affected by five basic parameters:
1. Signal strength from the GPS satellite.
2. Receiver/antenna gain.
3. Pre-amplifier noise figure.
4. Receiver noise bandwidth.
5. Accumulator sample rate and statistics.
The approximation is very accurate from 0 to 25 AMUs"

In TBoltMon under 'Packet Masks and Options'/
'Aux Byte (3)'/ 'Output dBc/Hz' you can set what 
kind of readout you want to see under 'AMU'
I have it set always to 'dBc/Hz and most of the
Satellites are coming in with up to 45 dBc/Hz.

A quick check (not easy because these beasts dont stop 
moving ;-) ) gives about the following values in AMU / dBc/Hz:

2 / 29
5 / 36
5.5 / 39
6.2 / 40
7 / 41
9 / 43
10 / 44
11 / 45

good luck,
cheers

Arnold



On Mon, 23 Nov 2009 22:58:53 +0000, Didier Juges wrote:

>How about Arithmetically Meaningless Units?

>Didier

>------Original Message------
>From: Tom Van Baak
>Sender: time-nuts-bounces at febo.com
>To: Time-Nuts
>ReplyTo: Tom Van Baak
>ReplyTo: Time-Nuts
>Subject: Re: [time-nuts] AMU vs dBc
>Sent: Nov 23, 2009 4:05 PM

>> A quick play with Gnumerics gave me the formula dBc = 20*log10(AMU)+25,5
>> to have the best match, and RMS error of 2,23 where as the dBc = AMU + 
>> 33,9 has the RMS error of 4,34.

>AMU
>Arbitrary Manufacturer Units
>Antenna Measurement Units
>Arbitrary Mystery Units

>See if these help your estimate:

>http://gauss.gge.unb.ca/papers.pdf/SNR.memo.pdf
>ftp://goes.gsfc.nasa.gov/pub/chesters/goesref/Moreau_GPS.pdf
>http://www.wavedigm.com/pdf/UG_smartGPS.pdf

>/tvb


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