Good points. Yes, I was just using the S11 method. I'll have to look at the Copper Mtn site and see if they found the same results we did relative to improved accuracy near the short and open points on the chart after calibrating for S11 measurement using SOL references. Thanks for the comments!

Wow. That's awesome. It's great to hear that the video was helpful and the port was successful. Your project sounds excellent!

Agreed. Thanks. I did get a little loose with that. But I would would argue that given variations in the measurement/calibration, frequency, and eventual application - that 5% is usually close enough 🙂

Thanks !

Thanks! 🙂

Agreed. It looks silly, but it's absolutely a technique I've used many times. But ONLY when its safe (low voltage, low-power receive circuits, isolated from the mains). That warning given, its kind of like tapping/pressing on stuff to find bad solder joints, or using freeze spray to find temp-sensitive things. In this case, at VHF and above, the finger adds some capacitance, but also power losses - which can stop the oscillation and hopefully help suggest where the feedback path may be. Of course it's not very scientific beyond that qualitative description - and as you said, how do we map changes in the observed behavior to ideas on tracking down the oscillation? It could always be that we're getting false clues. But any clues are better than no clues, IMO 🙂

@@MegawattKS awesome! Thank you so much! Also, quick question. Are you going to do a series on the Doppler radar?

@@ftscotttinez33 I've thought about that, but for various reasons decided against it (at least for now). FWIW, that class (as well as the one that Radio Design 101 is patterned after) are still taught at K-State.

Thanks. I noticed that too, but only recently. Hopefully you and I are more sensitive than most 🙂 I did notice that if I turned the volume lower, it was OK. Will try the solution(s) you mentioned before making new videos going forward (July 2024). Maybe RU-vid can create an AI filter to get rid of these artifacts in the existing ones ? ;-)

Thanks. Here's a link to a page in the companion website that has all the class stuff. The antenna hand-out is the second item on this page. ecefiles.org/rf-circuits-course-section-11/ (It took me a while to find where it was in all the uploaded materials, but I think this is what you're looking for.)

Yes - it goes to a low enough frequency that should be possible. It also has the ability to find the location of shorts (or opens) in a line partway to the load if that is suspected (using a frequency version of a reflectometer under Display>Transform). It's an amazing instrument comparable to the big expensive ones ! (Though the learning curve is sometimes a bit steep )

This is a "small" loop, so the circumference is much shorter than a wavelength. I basically created a scaled version of the commercial HF loop and then used a web search to estimate the L value to be able to select the resonating cap and then designed a different matching network from what they used. For a full-wavelength loop, yes - you can do that without a resonating cap - and it should be more efficient than a small loop - but you will not have the high selectivity on receive, since the high-Q resonance will not be in play. I did a Google search for "full wavelength loop antenna" and found this site - which seems to have a nice discussion of it. Hope that helps. practicalantennas.com/theory/loop/full-wave/

@@MegawattKS But how you calculated the size of the small loop? Is it (140/100)/10 * 100 = 14 cm? How you calculated the capacitor values?

@@debojitacharjee Sorry - I never reduced it to a set of equations. The video concentrates more on the evolution of the design, which as noted above started by scaling a 2 meter HF loop by a factor of 10 (from 10 MHz to 100 MHz). The design discussion begins around time 26:57 . The final loop shown in that discussion looks to be about 7cm in diameter - so about 22cm in circumference (a little more than 2m/10) - but since it's a small loop, the size is not critical, as the resonating capacitor will be tuned anyway. I think I recall that the nominal C for the resonating cap was around 16pF (it's somewhere in the video, but it's been almost a year, so I don't recall where). I did note by scanning the video that X_L is about 100 Ohms at 100 MHz, so that 16pF is about right. The harder part is figuring out the matching network - the "tap point" and the capacitor needed there. Unfortunately that part, while discussed, definitely needs more work before a set of equations can be given. It's quite dependent on the "tap point" and the Q of the final resonating loop. The best I can do is point to the discussion at 26:57 . Perhaps I or someone else can elaborate a procedure in the future (and maybe get this into the ARRL antenna book 🙂 ). But for now, we don't really have that. Sorry. (There is a commercial small loop shown around time 39:50 that is perhaps a little easier to build. I bought one and it wasn't nearly as good in performance, but perhaps if it was modified with a higher-Q tuning cap, it might do well...)

Sorry - I don't publish that. But I saw your question on another video - hopefully my answer was helpful. Feel free to ask questions in the public video comments. That way others with similar questions/ideas can benefit and/or help out as well.

Agreed. The net transmit plus receive antenna gain is 4dBi in a traditional Friis path-loss formulation for received signal level. (In the slide at timestamp 1:15 , a different derivation is used, but it's equivalent to the Friis, with Gr accounted for in Leff) But to the question of why do we lose much more power when we change position / polarization, the answer is that the "2dBi" gain quoted for a dipole only applies when the antennas are broadside and co-polarized. If they are not, then a dipole has lower gain than 2dBi. Indeed, when we go from broadside orientation to "endfire" as shown in the video, we see a huge drop in received signal. One way to think about this is to look at the fields shown on the graphic at 1:15 . For good reception, the receive antenna needs to be parallel to the E field that is coming at it. If it is not, then less total voltage (Vr = E * Leff) is induced. From the geometry, it should fall off as cosine(theta) where theta is the angle between the E field and the antenna element. Does that help answer the question?

@@MegawattKS thank you for your kind reply. I had thought that the phenomenon was due to the close proximity of the antennas which made the gain appear much stronger than normal.

Yes - I think so. It's been a while, but from looking at the pics and trying to remember, I think I had the other sig-gen output outputting the same waveform and used it to trigger the scope.

@@MegawattKS thanks, great videos by the way!

Hi. Here's the full Playlist. RF (small signal) amplifiers are covered in Episode 3. ru-vid.com/group/PL9Ox3wpnB0kqekAyz6blg4YdvoEMoJNJY and here's a link into that third episode where I've queued it up to the walkthrough of that amplifier. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-UUlqW-vSq9M.html The rest of the video covers lots of other background and variations - and there's a "Part 2" (called Appendix A) in the playlist for anyone who wants a deeper treatment.

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. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-UUlqW-vSq9M.html and ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-m9X0mfg_8lQ.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 RU-vid videos by RU-vid, 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. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-HJ-C4Incgpw.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: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-m9X0mfg_8lQ.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 🙂