Questions You Should Know about NEW AND USED BASEBAND

How should I tune the two baseband pairs of the 8-bit samplers? Similar considerations may apply to the 3-bit samplers that provide four baseband pairs.

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For the 8-bit samplers, the WIDAR correlator processes two independently tunable baseband pairs. There are a number of common applications; which one to choose is determined by the science you want to achieve.

• Tune end-to-end. This is often done if one wants to obtain as wide a contiguous bandwidth as possible. For instance, one 1 GHz baseband pair is tuned to 4.5 GHz, and the second to 5.5 GHz, for a complete 4&#;6 GHz coverage.
• Tune as far apart as possible within one band. Often used for spectral index determinations; for instance one 1 GHz baseband pair is tuned to 4.5 GHz and the second to 7.5 GHz, to obtain 4&#;5 GHz and 7&#;8 GHz coverage.
• Tune to target different spectral lines; for instance, one 8 MHz subband from a given baseband pair is tuned to the NH3(1,1) line at 23.695 GHz and a second 8 MHz subband from the other baseband pair to the NH3(5,5) line at 24.533 GHz. The basebands are not contiguous, but each covers the line of interest with the desired frequency resolution.
• Tune the two baseband pairs such that they are shifted by a fraction of one subband (i.e., largely overlapping). Each baseband pair consists of a number of subbands, and there is sharply decreased sensitivity at subband boundaries. When tuning the second baseband pair one-half of a subband width away from the first baseband pair, compromised data at a subband boundary in one baseband pair can be replaced by good data in the second baseband pair.

Note that the two baseband pairs offer two 'windows' on the available spectrum. If the baseband pairs overlap, the data in the overlapping part of the spectrum will be essentially identical in either baseband pair. This is why tuning both baseband pairs to the same frequency does not increase the S/N by &#;2.

In broadband, total bandwidth is
sliced among different channels.  For example  cable tv, each station
is allocated a slice of total bandwidth.  In cable we see these
channels  are analog.  But do they have to be?   For example in fiber
optic medium., we do the same thing  , transmitting multiple channels(
such as voice,data,video)  at the same time but in digital form.    So
i am observing that broadband medium    can carry multiple analog  as
well as digital signals as is the case with fiber.     The question
remains if i am correct in my observation.
Second
issue  is baseband does not mean point to point  communication.   
Point to point  communication means either we have dedicated link or
virtual link between two nodes.   As we know  ethernet is shared
medium,  for example  10base-T  using hub is good example   where base
signaling is used on a shared medium.
Thanks
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Baseband devotes the entire capacity of the medium to one communication channel. Broadband enables two or more communication channels to share the bandwidth of the communications medium. Baseband is the most common mode of operation. Most LANs function in baseband mode, for example. Baseband signaling can be accomplished with both analog and digital signals. Although you might not realize it, you have a great deal of experience with broadband transmissions. Consider, for example, that the TV cable coming into your house from an antenna or a cable provider is a broadband medium. Many television signals can share the bandwidth of the cable because each signal is modulated using a separately assigned frequency. You can use the television tuner to choose the channel you want to watch by selecting its frequency. This technique of dividing bandwidth into frequency bands is called 'Frequency-division Multiplexing' (FDM) and works only with analog signals. Another technique, called 'Time-division Multiplexing' (TDM), supports digital signals.

Yes you are right in broadband  signalling divides the network medium into multiple channels, allowing several signals to traverse the medium at the same time.

Baseband signaling only sends a single signal over the cable. This type of signaling is typically used in Ethernet networks, with the exception of 10Broad3 standard (rarely used). Baseband uses very simple transceiver devices that send and receive signals on a cable. The simplicity behind baseband signaling is that only three states need to be distinquished: one, zero and idle.

Broadband transceivers are much more complex because they must be able to distinquish those same states, but on multiple channels within the same cable. Because of its simplicity, baseband signaling is used on most Ethernet networks.

Hope to Help !!

Ganesh.H

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