Bandwidth Measurements - RF Cafe Forums
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Post subject: Bandwidth Measurements
Wed Jun 08, 2005 3:26 pm
Jun 08, 2005 3:17 pm
Location: Chesapeake, VA
like to know the following if anyone can help:
1. Why are 160
MHZ IF's measured at the 3dB point and 1 Ghz IF's measured at the 6dB
2. Is there such a thing as Effective Bandwidth? If so,
how is it actually measured?
3. Using an HP83640 and an HP8757
what is the best /preferred way to measure Bandwidth? I.E., Search Bandwidth,
Search Left, Search Right, or Delta it and do it by eyeball.
4. Are there any good books out there on performing RF, IF test measurements?
Any help would be greatly appreciated.
Unread postPosted: Thu Jun 16,
2005 9:16 am
Joined: Wed Jun 08, 2005
Location: Chesapeake, VA
subject: Bandwidth Measurement
Unread postPosted: Thu Jun 16, 2005
Unfortunately, the definition of bandwidth depends on
For filters, you use the Equivalent Noise Power Bandwidth:
The bandwidth of the perfect "brick-wall" filter which passes the same
noise power from an Additive White Gaussian Noise source.
communications systems planners, the amount of acceptable interference
determines the bandwidth. The 6 dB, 20 dB, 40 dB, and 60 dB points have
all been used historically.
For digital transmitter designs,
you have several choices:
1. The minimum-possible bandwidth, below
which errors cannot be reduced arbitrarily close to zero by controlling
Eb/No and group delay
2. The first-null to first-null bandwidth (for
ASK and PSK)
3. The bandwidth containing x% of the total transmitted
For analog FM, the Carson's Rule Bandwidth contains 98%
of the transmitted energy.
For analog AM, twice the highest frequency
present in the baseband.
You need to make a bandwidth measurement
- I presume that's because it matters to someone. Unless that someone
is a marketing droid with no technical knowledge looking for brochure
fodder, that person would be appropriate to ask.