Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
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My Hobby Website:
P1 dB - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: P1 dB Posted: Wed Nov 29, 2006 3:01 am
Joined: Tue Oct 03, 2006 3:03 am
What is the need and significance of P1 dB point
in the amplifier design
Posted: Wed Nov 29, 2006 7:48 am
Mon Jun 27, 2005 2:02 pm
gives an indication of the output power to which the amplifier is capable
to deliver before going into saturation.
Before the amplifier
reaches the P1dB it behaves linearly that means a linear relation between
its input power and output power. So if you increase the input power
by 1dB the output power will increase in 1dB as well.
doesn't enter sharply into the P1dB area. The output power becomes non-linear
before this point reaches. The gain will decrease gradually from the
linear gain G (Measured in small signal) to G-1dB. This can be seen
if you increase the input power dB by dB until you will reach the G-1dB
point in which the output power will be the P1dB [dBm]
Posted: Wed Nov 29, 2006 6:03 pm
Nov 29, 2006 5:51 pm
Actually the more precise definition
is the power at which the power response deviates from the linear response
by 1 dB.
In other words for instance when you have an amplfier
that has a gain of say 10 db you will see a difference between output
power and input power of 10 dB in the linear region. As you increase
the input power there is a point where the power amplifier starts saturating
and the power increases to a point that is less than the 10dB gain expected.
In this particular case of 10dB gain the output power at which the power
gain is 9dB instead of the expected 10dB is called the "1dB compression
Being that the 1dB compression is already deviated
from the linear response starting when it starts to compress this area
is not really useful for linear transmission. In most cases for acceptable
performance you need to back away from this point by 6 to 12 dB.
In most spread spectrum system when using non-linearized amplifiers
you usually use the 10dB backoff rule of thumb to get acceptable spectral
Post subject: Why not P2/P3 dB?Posted: Wed Jan 03, 2007 11:48 pm
Joined: Tue Oct 03, 2006 3:03 am
Why not P2/P3 dB?
Post subject: Posted: Fri Jan 05, 2007 5:09 pm
Joined: Mon Jun 27, 2005 2:02 pm
To the best of my knowledge, it is a matter
of industry standard definitions.
You can also choose P2dB,
P3dB. Actually there is a use for these figures for quantizing the AM/AM
curves of PA in order to generate opposite curves for pre-distortion