tag:blogger.com,1999:blog-1592992209402300549.post8221245346186528054..comments2024-03-28T08:06:43.198-04:00Comments on The Silicon Graybeard: A Ham Radio Series 19 – What is Phase Noise?SiGraybeardhttp://www.blogger.com/profile/00280583031339062059noreply@blogger.comBlogger7125tag:blogger.com,1999:blog-1592992209402300549.post-85848014312332787102020-11-30T22:38:36.439-05:002020-11-30T22:38:36.439-05:00I think you're right. The approximation of &q...I think you're right. The approximation of "AWG" noise ("Additive White Gaussian" noise is a convenient approximation that works for solving (or bounding) lots of problems. <br /><br />There's a concept called Johnson noise that describes the noise from thermal motion of electrons, N = kTBR where K is Boltzmann's Constant, T is temperature in Kelvin, B is the bandwidth (dimensionless, like Hertz) and R the resistance. Put a 50 ohm resistor on your work bench at 300K. According to the numbers, the power in that resistor is -174 dBm or 10^-17.4 milliwatts. We're not deliberately restricting its bandwidth in any way, so isn't the bandwidth infinite? Why isn't that noise much bigger? <br /><br />In reality, momma nature has restricted its bandwidth because no matter how you build that resistor there are stray inductances and capacitances that restrict its bandwidth. But kTBR is a very handy relationship that helps solve a lot of problems. <br /><br />Often, it's handy to work with approximations that "get close enough." <br /><br />Oh - and BTW, phase noise comes in different colors and is generally red. Or reddish.SiGraybeardhttps://www.blogger.com/profile/00280583031339062059noreply@blogger.comtag:blogger.com,1999:blog-1592992209402300549.post-56746137462234452732020-11-30T21:55:24.320-05:002020-11-30T21:55:24.320-05:00Some random things about random noise (or random m...Some random things about random noise (or random motion, which is how I first thought of it) that never really sat right with me: It doesn't seem to me like any physical system could possibly give you "pure white noise" on any real physical variable. At some point as you turn your bandwidth up, the noise has to die away.<br /><br />A "pure white noise" brownian motion of a particle would be one where the position at any given time is uncorrelated to any other time: The particle would blip from place to place faster than light. Real random-walks have real timescales over which the random-walk occurs (a maximum cutoff frequency), or you couldn't define an envelope containing the trajectory. <br /><br />I imagine the same must be the case for electrical noise. (I've heard the term "antenna temperature" before that probably relates to this.) I imagine they've swept this all under some quantum rug, but it seems to me like other physical limits would also apply to prevent even a classical process from generating noise of arbitrary bandwidth.<br /><br />MadRocketSciAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-1592992209402300549.post-84575620546934011772020-11-30T16:45:41.113-05:002020-11-30T16:45:41.113-05:00I want to make sure I understand the question, so ...I want to make sure I understand the question, so when you say phase shift, do you mean phase modulation (PM), like phase shift keying (PSK), or PM voice modulation? A lot of what are sold as FM transceivers are actually analog Phase Modulated transceivers, and it's hard to tell the two types apart. <br /><br />If you're talking about PM or PSK, it does degrade the accuracy of the phase shifts in those signals. In modern digital modulation, like 64 or 128 QAM (quadrature AM), they specify the transmitters by Error Vector Magnitude. Each symbol being transmitted has to hit its amplitude and phase shift precisely. Phase noise spreads out the accuracy of the point the modulator is trying to hit, and makes demodulation less accurate. Most ham uses are Biphase (180 degree) shifts, or Quadriphase (90 degree) shifts, and those are less affected by small amounts of noise. <br /><br />Phase shift has to be in comparison to another signal; phase shift is a measure of the time difference between them. So phase shift by itself doesn't mean anything to me. <br /><br />SiGraybeardhttps://www.blogger.com/profile/00280583031339062059noreply@blogger.comtag:blogger.com,1999:blog-1592992209402300549.post-86395678893652104712020-11-30T16:29:34.499-05:002020-11-30T16:29:34.499-05:00I am a ham with a General ticket, but got into the...I am a ham with a General ticket, but got into the hobby in 1972, so I started out as a novice, so I also have the Morse Code endorsement, from my Tech Plus year. It has been a long time since I dealt with this type of technical detail. Life gets in the way, sometimes. <br />My question probably will sound stupid, but does phase shift affect how phase noise reacts? And is that a way to attack phase noise, by trying to reduce the phase shift? This topic is kind of over my head, and I am just trying to wrap my head around it. But I do thank you for addressing ham radio, and topics like this. I am in the process of getting back into HF and have a QRP kit that I am going to build soon. Best wishes, for the coming new year.<br /><br />pigpen51Pigpen51https://www.blogger.com/profile/01683463718454987063noreply@blogger.comtag:blogger.com,1999:blog-1592992209402300549.post-46296035173702735722020-11-30T06:56:09.418-05:002020-11-30T06:56:09.418-05:00In electronics, as in all of life, TANSTAAFL.
You ...In electronics, as in all of life, TANSTAAFL.<br />You get what you pay for.McChuckhttps://www.blogger.com/profile/10243337792601085456noreply@blogger.comtag:blogger.com,1999:blog-1592992209402300549.post-17546626405105721452020-11-30T01:35:15.547-05:002020-11-30T01:35:15.547-05:00Thank you very much...againThank you very much...againboronhttps://www.blogger.com/profile/05780356895910449471noreply@blogger.comtag:blogger.com,1999:blog-1592992209402300549.post-41602968483799159972020-11-30T01:03:40.063-05:002020-11-30T01:03:40.063-05:00I worked on some low-noise crystal oscillators at ...I worked on some low-noise crystal oscillators at Hughes.<br /><br />How good were they? We had to do the final test and alignment in a screen room to ensure we were looking ONLY at the DUT, and we ran it on battery power, like it would be in use. We were pushing the limits of the top of the line HP test equipment we were using.drjimhttps://www.blogger.com/profile/05647484115197408897noreply@blogger.com