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...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
phase noise doubler - 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: phase noise Posted: Wed Apr 05, 2006 11:52 am
Joined: Wed Apr 05, 2006 11:42 am
Who can explain why phase noise after doubler increase by 20log2=6dB
and not 10log2=3dB ?
Phase noisePosted: Wed Apr 05, 2006 7:18 pm
Joined: Wed Feb 22, 2006 3:51 pm
a doubler, there are intermodulation products added, as well as harmonic
products. See Steven Maas' book Nonlinear Microwave & RF Circuits
for more details.
Post subject: Posted: Thu Apr 06, 2006 10:02 am
Joined: Mon Jun 27, 2005 2:02 pm
Without reading the book so far, intermodulations
and harmonics are considered as signals and not noise, so how can they
increase the phase noise?
Post subject: Phase NoisePosted:
Thu Apr 06, 2006 4:55 pm
Joined: Wed Feb
22, 2006 3:51 pm
Sorry, yz, I misread your question,
and answered a similar but not identical question about why performance
is often worse than 20 log n.
The quick answer to yz's question
is that phase noise comes from undesired phase modulation of the carrier
by noise. The amplitude of the sidebands is determined by the modulation
index (approximately a linear dependence at low modulation indexes).
The modulation index doubles when the frequency is doubled. Since power
is voltage squared, the 10 log for dB becomes 20 log : log v squared
= 2 log v.
Signals and noise are ultimately indistinguishable.
If you could distinguish them in any way, noise could be removed from
a corrupted signal - an outcome we'd all stand up and cheer for! Considering
phase noise as resulting from incidental phase modulation by noise (usually
device noise) is a standard approach.
Sometimes principles are
easier to see when discussed in sine wave terms, which is why the distinction
sometimes gets made.
In this case (and again, my apologies for
answering the wrong question), sometimes you see worse-than-20 log n
performance due to the intermodulation products.