Is there an AN which describes how to measure the (Co+No)/No of digitally modulated carrier ?

Does it matter what RW is used ?

Do the correction factors used in CW C/N measurements apply ?

Does it matter what RW is used ?

Do the correction factors used in CW C/N measurements apply ?

I'm trying to find out what can be done in terms of measurement and interpretation of that measurement, of a digitally modulated carrier, when it's not possible to look at the same carrier unmodulated.

Unfortunately, there is no other application note that explains the carrier-to-noise ratio with details about the questions you have raised. However, user XMO did recommend correctly AN 1303 as an updated guide for making these types of measurements on modern analyzers (like Agilent's X-Series analyzers).

First, let me address your question about RBW and corrections. If you refer to AN 150-4, Chapter 3, it provides the steps for making a carrier-to-noise measurement. It states that the measurement is normalized to the receive bandwidth of the signal. Therefore, if the receive signal bandwidth is a TV signal such as the one mentioned in the app note, the carrier bandwidth is 6 MHz. For noise-like signals, in order to measure the carrier power, we need to make a "channel power" or "carrier power" measurement. The description for this type of measurement in modern analyzers is located on pages 14-16 of AN 1303. Essentially, we integrate the total power in the given bandwidth. The total integrated power is normalized by the noise bandwidth of the RBW used, and therefore, the measurement is independent of RBW. The only consideration to make is that for large RBW's, there is additional bandwidth uncertainty (power bandwidth accuracy) introduced. For large C/N ratios, the addition of noise to the carrier power is negligible. If it is desired to remove this effect, the noise power can be subtracted from this total channel power before calculating the ratio.

Next we need to make the noise power measurement. The app note 1303 also describes how this is done automatically in modern analyzers using the noise marker function. The user can specify the bandwidth (6 MHz in our example). See page 9 of AN 1303 for more details about the noise marker. This marker corrects for under- and over- responses due to the way we display the results in the analyzer, as well as the equivalent noise bandwidth.

Finally, we can take the ratio of these to get the carrier to noise ratio as described in AN 150-4

Your other question was about Ebi/No. Since the energy per bit to noise ratio is related to the C/N ratio by a factor of (bitrate/channel bandwidth), it is easy to calculate a required C/N ratio from a given Ebi/No. Simply multiply the Ebi/No by the bitrate/channel bandwidth to get the required C/N. This is true because the energy per bit times the bitrate/bandwidth is the power per unit bandwidth. We do not have an application note that addresses this for generic digital measurements, but it is covered at the top of page 43 in AN 1355. Note that the channel bandwidth in this app note example is 3.84 MHz. The equation in this app note is for units of dB.

http://cp.literature.agilent.com/litweb/pdf/5980-1239E.pdf

Please let me know if I can be of additional assistance.

Best Regards,

Scott

I have a document with unknown origin suggesting that from the measured (Co+No)/No of digitally modulated carriers, Ebi/No can be derived and knowing the Ebi/No requirement, the required (Co+No)/No can be calculated.

The document also states that it does not metter what RBW is used, because the measurement is for Carrier Density (Co) and Noise Density (No).

The document shows the steps for the calculation. If the content is true, this would be a very useful process. Nowadys most often it's not possible to make true C/N measuremnts with CW carriers.

I'm looking for varification of the process outlined in the document.