Post by LutzvW on Jan 29, 2005 11:49:44 GMT -5
To understand the theoretical background and the technical consequences of the tutorial on link budgets some comments/corrections are to be made.
1.) General comment:
In the tutorial, there is a confusion about levels in dB. It should be kept in mind, that the log operation is to be performed only for pure figures (without dimensions). Therefore, each physical parameter must be normalized first (e.g. division by 1Watt leads to dBW, and division by 1 Hz leads to dBHz). Thus, the levels in the middle of page 10 are correctly written, however, this is NOT the case on most of the other pages and can lead to some confusions.
2.) Examples:
page 3/ex.1: 13 dBW/Hz instead of dB
page 3/ex.2: -23.9 dBW/Hz instead of dB
page 4: C/N in dB; Rb in dBHz ; B in dBHz; C/No in dBHz
page 6: EIRP in dBW instead of dB
page 6/Ex.3: Flux Density in dBW/m2 instead of dB
page 13/Ex. 5: G/T in db/K instead of dB
It is very important to know (and to indicate) the normalizing value, otherwise the dB information is useless.
As an additional example, look at pages 17, 18 and 22. Here, the question arises which figure is used for the Boltzmann constant to express k in the dB domaine. Four of the several alternatives are mentioned on page 10.
3.) Table on page 5: The information in line 3 is obviously incorrect. If the bandwidth increases all signal-to-noise ratios decreases accordingly.
4.) page 6: From the engineering point of view it is not correct to state, that an antenna „further amplifies the power“. The antenna does nothing else than to focus the transmitted electromagnetic waves – thereby reducing the free space loss (by its gain value) as the formula for this loss assumes an isotropic transmitting antenna.
Therefore, the abbreviation EIRP means „Equivalent Isotropic Radiated Power“ (a pure abstract resp. Theoretical value).
5.) page 22: For my opinion, the inclusion of input/output back-off effects into a tutorial on link budgets is not appropriate, as this is a very special method used only in turnaround –transponders with multi-carrier operation. Instead, It confuses the reader who is interested in the basic principles of link design
6.) Finally, I like to point to two links which further explains the whole subject (especially the influence of noise as in the tutorial all noise aspects are treated rather roughly.)
satsig.net/linkbugt.htm
and satsig.net/noise.htm
Nevertheless, I appreciate the intention to install a platform like this for discussion of actual technical subjects.
Lutz v. Wangenheim (Bremen, Germany)
1.) General comment:
In the tutorial, there is a confusion about levels in dB. It should be kept in mind, that the log operation is to be performed only for pure figures (without dimensions). Therefore, each physical parameter must be normalized first (e.g. division by 1Watt leads to dBW, and division by 1 Hz leads to dBHz). Thus, the levels in the middle of page 10 are correctly written, however, this is NOT the case on most of the other pages and can lead to some confusions.
2.) Examples:
page 3/ex.1: 13 dBW/Hz instead of dB
page 3/ex.2: -23.9 dBW/Hz instead of dB
page 4: C/N in dB; Rb in dBHz ; B in dBHz; C/No in dBHz
page 6: EIRP in dBW instead of dB
page 6/Ex.3: Flux Density in dBW/m2 instead of dB
page 13/Ex. 5: G/T in db/K instead of dB
It is very important to know (and to indicate) the normalizing value, otherwise the dB information is useless.
As an additional example, look at pages 17, 18 and 22. Here, the question arises which figure is used for the Boltzmann constant to express k in the dB domaine. Four of the several alternatives are mentioned on page 10.
3.) Table on page 5: The information in line 3 is obviously incorrect. If the bandwidth increases all signal-to-noise ratios decreases accordingly.
4.) page 6: From the engineering point of view it is not correct to state, that an antenna „further amplifies the power“. The antenna does nothing else than to focus the transmitted electromagnetic waves – thereby reducing the free space loss (by its gain value) as the formula for this loss assumes an isotropic transmitting antenna.
Therefore, the abbreviation EIRP means „Equivalent Isotropic Radiated Power“ (a pure abstract resp. Theoretical value).
5.) page 22: For my opinion, the inclusion of input/output back-off effects into a tutorial on link budgets is not appropriate, as this is a very special method used only in turnaround –transponders with multi-carrier operation. Instead, It confuses the reader who is interested in the basic principles of link design
6.) Finally, I like to point to two links which further explains the whole subject (especially the influence of noise as in the tutorial all noise aspects are treated rather roughly.)
satsig.net/linkbugt.htm
and satsig.net/noise.htm
Nevertheless, I appreciate the intention to install a platform like this for discussion of actual technical subjects.
Lutz v. Wangenheim (Bremen, Germany)