Відео

Good question. Yes - for common-emitter amps, we feed at the base and put a bypass cap to ground the emitter. The intent is to vary the base-emitter voltage with the signal, which is the first step in the amplification process. Here we chose to feed the signal in at the emitter and bypass the base. - so the base-to-emitter voltage is still varied and the amount of voltage amplification can still be the same (though the input resistance is less). This is called a common-base configuration. Details can be found in Episode 3 ("RF Amplifiers"). And even a deeper dive is presented in Appendix A. ua-cam.com/video/UUlqW-vSq9M/v-deo.html and ua-cam.com/video/m9X0mfg_8lQ/v-deo.html

(edited) Technically, the main changes/additions I can think of would be the need for AM demodulation of course, adding some form of AGC, and you probably need a more narrow IF filter. A few years in the university course we did some variations on the FM broadcast theme to be able to receive NOAA weather radio (at around 151 to 156 MHz). The NOAA signal bandwidth was also only about 5 kHz, so we had to find a suitable IF filter - and I think we went with a dual-conversion receiver architecture. But the signal was still FM (narrowband). For AM, a different demod would be needed. The demod shown in this series wouldn't work because it's specifically for FM. I'll look for options and add a second reply.

This is a follow-up to the reply above (now edited). I forgot to mention the need for auto-gain-control (AGC) initially as another factor, and when I went looking for an AM demod I realized we were still doing (narrowband) FM. Since that reply was written, I've searched for commercial ICs that might be useful for AM demod. Sadly, I haven't found any. I'm starting to think that AM has been left behind in more ways than one. In the course, we start with AM, but then moved to FM and digital modulations that are more commonly used now. For AM, we discussed the classic envelope detector, but also "synchronous" detection using a mixer. Alternatively it might be fun to try using a modern "linear detector" IC like this as a demod www.ti.com/lit/ds/symlink/lmh2120.pdf (just a wild idea as that is not the intended market for this little guy). Now-adays, I think most people would opt to build the receiver out as far as the filtered IF and then digitize that and do the AM demod function in software, perhaps.

The ads are placed in UA-cam videos by UA-cam, and we have no control over them (unless perhaps a channel is monetized, which this one is not). That said, I don't think there's a plausible mechanism for infection if you don't click on something to follow a link somewhere. AFAIK, ads are just other streamed video - not software. Hope that helps.

Thanks. Yes - a long-wire was very the first antenna I used. Wish I had had a NanoVNA back then!

The multimeter shown at timestamp 1:18 is just set on Ohms. For this DMM, this is the "auto-range" setting for measuring DC resistance. I think they implement auto-range by trying each range and finding the lowest range that gives a non-overload reading (this is done to maximize precision in the reading). In this case it responded very quickly because they probably start at the lowest range (1000 Ohms) and it didn't overange there - so it doesn't have to try any more ranges and they just report that reading (51.0 initially and 50.9 later). In practice, I would just say it reads "51 Ohms" because the last decimal place won't affect the dummy loads ability to do what it needs to. It just has to present something resembling 50 Ohms to the DUT (Device Under Test).

@@MegawattKS thank you

You are very welcome. I appreciate your feedback and knowing that the presentations are helpful. I use Powerpoint to make the slides. I've also found that using the Windows "Snipping Tool" helps in bringing in photos/etc with simple cntl-C and cntl-V keyboard shortcuts. Plus I use some image editing programs I have to modify 'gamma', etc if the videos are not light enough for example. A lot of the circuit diagrams are hand-drawn in Powerpoint using their "Shapes" menu - and I confess I have mixed feelings about the PPT user interface there. But over time I've begun to appreciate it (including the equation editor). For the assembling the videos themselves, it's a collection of things. A couple Canon cameras for taking main video shots and photos. And then Pinnacle Studio for assembling/editing. I also use MultCam Capture for adding the voiceovers. I don't recall where it came from, but It works for marking an area of the computer screen and 'filming' that while using a microphone to overlay sound when going through the PPT slides. I'm sure there are better ways to do that, and most if not all of these things - but this is what I accumulated over the years 🙂

You are very welcome. Thanks for leaving this comment !

Sorry - I don't have any info on that. I sold the car a year or two after this was done, unfortunately.

@@MegawattKS Thanks anyway

Yep. Fun stuff. Along with Laplace (which is the continuous time version). I've been hesitant to tackle that math in too much depth so far. BUT - I did recently find this excellent video on the "Curio Res" channel. ua-cam.com/video/HJ-C4Incgpw/v-deo.html She has put together an amazing video for those interested in Arduino _implementations_ of digital lowpass filters. Some Z domain transfer functions and associated difference equations show up a little after 3 minutes 30 seconds into it. I like her presentation style, and she shows coding too :-)

Very glad it helped. I owe some of the production to Pinnacle Studio and the ability to cut out pauses and "ah"s and such 🙂 Not sure where to go next. Thanks for leaving this encouragement.

You're very welcome. Thanks for leaving the comment.

Good to learn. Thanks for the info! I always use ear plugs when sounds are above 100 to 120 dB. Went to a concert once in my teens where my ears "rang" for about 30 minutes after it let out. I figured that was bad - so I never repeated that mistake. Fortunately, I still have pretty good hearing 50 years later. Just the usual loss above about 10 or 12 kHz.

Thanks! It's not really that, but I'm glad it at least seems good. Thanks for the encouraging words!

Wow. You're welcome. Thanks for the comments!

Thanks! Glad it was helpful. I finally got around to making a "Part 2" to this episode which goes into some of the background/theory in more depth. It can be found here: ua-cam.com/video/m9X0mfg_8lQ/v-deo.html (Thanks to your comment, I also added the link to it in this video's description so it's findable by others too :-) )

@@MegawattKS i appreciate your effort, thank you again bro. indeed , i follow and watch all your esteem channel's videos, you deserve it. sincerely

@@MegawattKS also i shared it ,

Thanks for this good point. Yes - that's one of those ingenious ideas that can be employed when the math is embraced 🙂 My cable modem is using 256 QAM I believe, allowing 8 'bits-per-Hz' (or 48 Mbps in the space of one 6 MHz 'channel'). Two related things for those interested include the Shannon-Hartley limit on bits-per-Hz that can be achieved in theory, and OFDM modulation that actually employs the FFT (and inverse-FFT) together with QPSK or QAM to do this on messy wireless 'channels' that have fading. Fair warning: Each of these topics is very deep mathematically. But here's a good overview of OFDM and its use of FFTs: helpfiles.keysight.com/csg/89600B/Webhelp/Subsystems/wlan-ofdm/content/ofdm_basicprinciplesoverview.htm

Wow. That brings back memories. Old UHF TV tuners could also receive in that range as I recall. That's where the original cell spectrum came from in the US (channels above 69). Good question about the scanner regs. I don't know. But even as they were rolling out the regs, cell phones switched to digital modulations so it became a non-issue anyway, I think.

@@MegawattKS Analog service was slowly phased out even as digital service started to replace it. I was told that the very last analog site to be decommissioned was in Death Valley, CA. (Sort of fitting.) I remember when the old UHF TV tuners were analog (continuously tunable), until the FCC required manufacturers to provide channel detents. The weird thing now is the ATSC channel numbering system. I used to wonder why KABC channel 7 was so difficult to receive. Then I found out. They're about the only area channel to retain a *VHF* frequency. Most antennas (antennae?) are optimized for the UHF band.

Thanks.. That's probably a good way to get the phase information too! I didn't know they had a real-time version for this. Does it tie into the audio system of the computer so you can use a microphone/etc ?

Thank you !

Thanks - glad it helped !

Thanks! Glad you liked it.

Thanks! I watched your video on your loop antennas too. Beautifully made.

@@MegawattKS Glad you like it!

Thanks. I think I found it and am watching it now - trying to figure out if/how frequency tuning is done. The design seems to be a little different in not having a resonating cap - but it's hard to tell. I'm also a little confused about the bandwidth. It talks about the narrow bandwidth in the early part, but then later they talk about 442 MHz BW at 2.45 GHz - which is not super narrowband... Anyway it looks cool 🙂

I bought these at RockAuto. I just did a quick look and don't see HID for the '07 Avalon currently. Checking my records, it looks like they had HID ones back in 2018 (for $950 each, vs $126 each for these), under "TOYOTA>2007>AVALON>3.5L V6>Body>Headlamp Assembly". But I don't even seem them now... Sorry.

Sorry - I don't have any books on the topic. Doing some web searches, I notice there are a few, but they tend to be large and expensive - and like any books, one needs to be sure they fit what one is looking for. I'd like to pick one and suggest it, but it is unlikely I would pick a good fit without knowing a lot more about your background, goals and areas of interest. The points I mentioned in the video are just from my own life experience. I was lucky to learn some of the basics when I worked in a TV repair shop many decades ago. It is interesting how those skills applied in so many areas of life going forward.

You're welcome !

Hi. The short answer is that it is roughly equal to 1/gm, where gm = Ic/(0.04) for the transistor used. So when biased at about 4 mA for Ic, Rin = 10 Ohms. A much longer answer is given in Part 2 of the video here: ua-cam.com/video/m9X0mfg_8lQ/v-deo.html . I queued that up to the part that shows the formulas. As mentioned there, the formulas given in the slides for the different configurations are found in textbooks - but the Part 2 video presents the model for the transistor that is used in those derivations :-)

@@MegawattKS that's great, thank you!

Glad it was helpful ! 73's

Well said !

Welcome aboard. Glad it resonated (pun intended ;-) ).

Thanks. That's good to hear (pun intended ;-) On the question: The half-as-loud should be the -10 dB one. But its very subjective, by definition. Interestingly when I was playing it back on my PC, the -10 dB section sounded a bit less than half as loud to me as the reference section - maybe 1/3'ish. And at -30, it seemed almost gone. But when I played it on my better speakers, it seemed about half as loud at -10 dB - agreeing with what the literature suggests. I suspect it depends on how loud stuff is when listening, maybe ?

I was a little worried about the 10 vs 20 dB thing when making the video but opted for leaving out the somewhat dry math derivation :-) It's confusing for sure. The 10 vs 20 multiplier in the formulas doesn't change the dB value. Its just how you get to dB from amplitude or power. If you already have a power ratio - then you use 10 log. But if it's voltage, its 20 log. That's because with a voltage ratio of V2/V1, the associated power ratio is (V2^/R)/(V1^2/R) = (V2/V1)^2, and 10 log [(V2/V1)^2] = 20 log (V2/V1) by the rules of logarithms...

You're welcome! Glad you liked it.

Glad you enjoyed it. Thanks for the note.

Thanks for the comments. Oh gosh. I hope we're not the last of a dying breed. But I have been wondering similar things about AI's effects on humanity if/when we get to AGI. I was watching an interview and Q&A with Sam Altman last night on UA-cam (from an ETL seminar held at Stanford). The issue you raised was not addressed - until one person at the end asked about it. Altman's answer didn't really help IMO. He seems blind to that. But some of his earlier comments on slow rollouts and viewing AI as another tech to help in joint discovery were slightly encouraging. Glad to hear you've got a lab and are getting into RF technology ! Thanks for your thoughtful remarks. You have a good way of expressing these issues. 73's

Thank you!

Glad it was helpful! I finally added a "Part 2" for this, but it's in the Appendices :-) ; ua-cam.com/video/m9X0mfg_8lQ/v-deo.html

Glad you like them. 73 !

I'm sorry, I said something incorrect, because I forgot to mention the load!: as you say in the video, the impedance transformation would be made from the resistive load (I guess in parallel with the Rp of the secondary coil) to a lower resistive value in the primary, according to the square of the turns ratio. But then, on the primary side, there's no capacitor to resonate or cancel the reactive component of the primary coil. Does this reactance appear or how is it taken away from the transformed impedance? Thank you.

Sorry for the delay in replying. This is an excellent question. I saw your followup info too. Will try to answer both here. On the issue of the primary winding L showing up, I would argue that it would be in parallel, not series. Beyond that, we need schematics and some math to really work it out. But qualitatively, I would offer that the primary and secondary inductances are linked (coupled magnetically), and that there is a mutual inductance involved. So with the secondary resonated, the inductance in the primary is part of that resonance already. This assumes either a good "coupling coefficient" value K, and/or an LC tank circuit Q on one side that is > 1/K. Here's some of the math. Sorry the writing is bad. These are from my class notes and it's a little light on the derivation since I just used these to remind me of what I wanted to talk through. Hopefully some of it will help. ecefiles.org/rf-circuits-course-section-13/

Note that the equations at the bottom of page 1, the circuit model at the top of page 2, and the application circuit in the middle of page 2 are for well-coupled inductors, but without a core. The model includes an "ideal transformer" in it, but the actual construction does not. It's just a simplified model for reasoning through the circuit operation without having to invoke the equations from page 1 again...

Thanks!