SWR Demystified: AD#28
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- เผยแพร่เมื่อ 17 พ.ค. 2016
- SWR, or standing wave ratio, always comes up when discussing antennas and feedlines. Although it's by no means the most important element of antenna performance, it's the easiest to measure, and thus probably the parameter most talked about. This video explores SWR in some detail. Thank you for watching my videos! My channel, "Ham Radio Answers," is here to help you become an active, on-the-air amateur radio operator! I am unique in that I provide the only set of TH-cam training videos that accompany the ARRL license manuals, section for section. I try hard to answer every Ask Dave question individually if I can.
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This is the best and most helpful explanation of SWR that I've encountered. I take my Technician's test in two weeks.
How’d ya do? Taking mine Saturday. Got 33 out of 35 today on the pre test 👍🏻
One of the best explanations of VSWR on TH-cam
Thanks Dave,
While I already knew most of what was presented here, even an EXTRA class has a few things left to learn. I love that you get into the math. This is where so many others shy away because they are afraid of intimidating their audience. The truth is some of these things are just complex and there's no getting around that by watering it down. Thanks again for giving it to us full strength!
This video cleared doubts and questions I didn't know how to even ask! Thank you
Thanks for all your effort on the videos! Extremely well done and important, useful topics. So much can be confused on many blogs and your primers offer valuable baseline info.
Video is 6 years old and it's a classic. Thanks for all you do for radio ops everywhere.
Thank you for the best of presentations and you as an instructor, are unequaled. Appreciative former instructor. 73, Tom K9FLY
once again Dave, you have made another excellent value video offering that is totally comprehensible and easier to understand than anything else available! Thank you and 73!
KA0RSN
Incredible. I’ve just begun to study for my extra. This video is enlightening. I’ll probably watch it a dozen more times.
This comes at the right time. I'm currently studying for my Amateur Extra license. Thanks for posting. I look forward to future videos you post here & 73...
Simple and clear excellent explanation! Thank you.
Well explained, thanks David.
I greatly appreciated your video. It answered some things for me, I did not realize before. Thank you for your videos, you would make a hell of a good elmer for someone, and a teacher for a class.
Thanks again Dave. Outstanding.
Great video! Love the theme music too!
Very nicely done Dave.
Thank you for your work. It is appreciated!
73, Harv WB6TTF
Best explanations i've seen on this subject.
Well done Dave!
Wow, Im only half way through and you have already answered a lot of my questions. I have my technician license and just attended a whole general course.
Thanks! This was a real kindness!
Thank you, Dave. I was completely befuddled, but now I think I might know which way is up. No doubt I'll be watching this several more times.
Cheers!
Neil, KJ7BNH
Dave,
Thanks for making the subject of SWR much more comprehensible.
WB3BJU
Wonderful explanation, just the right amount of math and theory, thank you!
Thanks David...I've been an amateur since I was 15/16 I'm near 60 years soon, somewhere along the way I've simply forgotten a lot of the basics which is sad....this video has renewed a few of the concepts and I thank you for that....as a result I've subscribed!...Cheers Clint - VK3CSJ Melbourne
Dave, great video. I'm new to this, and I think I now have a good grasp on the concepts of SWR. I'm afraid my algebra skills are lacking. Time for a refresher on those! Thanks.
Awesome video. Perfect balance to keep it going smooth. Refreshing myself with all of this that first learned in SATCOM tech school back in the 90’s. Just getting into amateur radio and studying Elements Three and Four material. I’d like to get a GROL as well...
Outstanding explanation very useful and interesting.. Thanks a lot
Excellent video, thanks
You are a excellent presenter. Great job! I leered allot
This is the best video explanation on this subject that I've ever seen! Great job Dave!
I learned something that my piece of paper states that I already knew......
I know so little about radio that by the time I am 60 I will know virtually nothing.
Call me Sgt Shultz - I know nothing.
Thanks for the most informative explanation of Reactance curves and formulae.
Well, I have just turned 70 and have forgotten most things....Hi Hi....VK2LEE Lee
Hi Dave, thank you very much for this video! I'm new to ham radio and I keep seeing the plots of SWR without having any intuition of what it is all about. Your video helped me finally understand what it means.
Great explanation very help ful
In my books you went from a really knowledgeable guy to the smartest person I know. I have not worked bands in 20 years, but now that i am close to retirement i am getting back into it. Your series makes me feel like a brand new ham all over again.
Welcome back to ham radio!
Many thanks, Sir !
Here in old Germany/ Switzerland, we use the highly academic ,,antenna bible,, written by a man named ,,Rothammel,, ... your summary and the graphs at end of presentation are much more of practical and clear to understand basics type, i.e. ,,both feet on the ground,,
73 de HB9
Great video, Thanks.
Great! Learned a lot!!!!
the fact that you guys need a video on SWR truly explains why it's called AMATEUR radio.
Fantastic! Thank you.
Awesome info! I would never get this out of a book only
Perhaps the most cordial, clear and pleasant explanation i've ever come across on you tube
Thank you!
This was great for where I am. Now I just need to learn how to measure the loss in my cables.
Great video! I'd like to add that an antenna can have multiple resonant frequencies. The antenna is resonant when the inductive reactance and capacitive reactance cancel each other and we're left with a purely resistive load. This occurs at multiple frequencies for a given antenna.
Absolutely! The chart I showed in fact had three points of resonance, and if the frequency range had been extended more, there would have been more. Also, multi- band antennas can be made with points of resonance in all the useful places. As I pointed out in the video, the equations I derived were only valid very close to 1/2 wavelength. But, generally an antenna will have only one resonant point per band.
Very good. Well explained.
73, Bill, G4GHB.
I just found this vid. Love it. Dave I am a Technician. I talk on 10m and still use 11m because I have more access to people helping me figure things out. Even though those are not ham guys they still like to use wire antennas and make their own.
Here is my situation if you could elaborate on this for me it would help me and my friends understand where we are.
we are all using 1/2" alum tubing and then smaller piece on the end to slide back and forth to get the SWR correct. I have the alum tubing inside of 1/2" schedule 40 pvc pipe and it fits nice and tight and is sealed properly so no water gets inside. I have a 50 ohm coax connected to the feed point. I have the tubing 2 inches apart and the ground braid and the center line connected about 1.5 inches or so apart to a screw head on each piece of tubing going all the way in to the other side of the tubing so it is connected on both sides of the alum tubing with each screw and the wire wrapped around and soldered to the head of each screw. I am trying to figure out what the length is for 11 meters or 10 meters. I use 11 meters because I have people I can readily use to test etc .. ok .. I would do 10 meters but nobody is locally on where I live that I can get them to test with me did contact with a few guys locally but they don't give you time of day ham guys that is ... sooooooooooo
1. What length should I start off with for 11 or 10 meters. I do use the formula to get the length of a dipole for 26.965 to 27.405. Says it should be 103".
2. I started with 102 1/2 inches and got an SWR on 27.405 at 1.56 and 26.965 an SWR of 1.22 using a Rig Expert. I have the antenna in a vertical position.
3. Coax is 50 ohms and at the antenna feed point is 72.5 ohms based on what I read. How do I know what the impedance or ohms is at the dipole feed point if it is not 72.5 ohms.
4. I looked this up on the internet and the article says on a dipole you can't get any better than a 1.45 SWR on a dipole. Feed point is 72.5 ohms and the 50 ohm coax = 72.5 ohms / 50 ohms = 1.45 SWR.
They said that lots of people keep cutting down the lengths of the dipole until they get a 1:1 SWR. Which is not good because you may have a SWR 1:1 but the antenna will not perform well because it is so much shorter than it should be after cutting it down for SWR. This is where I am lost ... If 1:1 SWR is not important or required then how do you know how long the antenna should be .. all my amps will not work on a SWR greater than 1.2 or 3 properly they get hot or burn up .. so with an SWR of 1.45, connecting point at a 11 meter (27.965 to 27.405) dipole is 72.5 ohms and 50 ohm coax what length should each side of the 1/2 wave dipole be then?
I have spent I mean to tell you hours and hours and hours cutting and wasting so much wire I decided to go to aluminum tubing so i can just slide it back and forth and not cut the wire etc. I know what I typed sounds strange or even confusing which is so true I am confused .. I read sooooooooooooooooooooooooooooooooooooooooooooooooooo many freaking things about what to do and nobody is consistent. After watching what you just demonstrated in this vid I know what I am doing basically is not right. I am really trying Dave it is not something I come to you without many many hours of trying and reading and reading and reading about SWR. I literally use two different SWR meters and a Rig Expert and I cannot for the life of me figure out the correct antenna length for a good 1/2 dipole .. at this point I am over the 1:1 SWR thing ... I just need to know how long should my dipole be for 26.965 to 27.405 without worrying about the SWR. I just want to know what the correct length is without sacrificing the integrity of a proper dipole ... sure could use your help DAVE I know I am nothing compared to you or other hams out there but I am wanting to learn along with my buddies .. thanks Dave i watch you all the time.
Terry
and I thought I had a solid understanding of SWR. boy was i wrong! lots more for me to learn. I am only vaguely familiar with alot of the core terminology in this video, so looks like time for some background study! i've always heard that long runs of coax can mask a bad SWR, and now i know WHY! your videos are always so well done. thanks for putting the time in to educate us!
I was able to keep up with you pretty well with all this, ( but I have been fairly familiar with the subjects for about 50 years,) however I am sure that many newer hams found all of this material covered in only 1/2 hour, was probably WAY too much to absorb! At any rate, I found it to be a refreshingly original approach to the material!
Reflected power is like a pendulum if the transmitter is tuned to the antenna's complex impedance. The reflected power is continously re-reflected while constantly being reduced by mainly cable losses. The point is that all transmitter power, less mainly cable losses, will be radiated by the antenna if the antenna is tuned to resonance using an internal or external tuner.
To simplify, if your tuner can tune a 3:1 SWR antenna to a complex impedance of 50+j0, it will radiate close to 90-95% of transmitter power with a low loss coax cable or ladder line. Of course, you should always try to build your antenna to get the lowest SWR considering the time and effort to do so. As you stated most tuners can tune a 3:1 antenna to resonance. Tuner losses are usually very low.
Thanks for the explanation. 73
excellent !
Very good video, thank you for posting this. 73 W5SRT
For 15 years I had no SWR meter and fellow amateurs were horrified when I tuned my long wire simply for maximum radiation out using an r.f. detector, I never blew the home brew h.f. rig. When I did make an SWR meter about 5 years ago it showed it was correct, maximum power out coincided with a good SWR.
It's a resistive Wheatstone bridge type. The limiting factor is the power handling capability of the resistors but I use QRP so it's not a problem, 5 Watts will give a 1mA meter full scale deflection with a little more to spare for adjustment.
I love playing with aerials, I have an inverted vee for 40m, made a dipole two years ago when I got on 2m, then recently made a Super J Pole and last week turned it into a 4 element centre fed Franklin collinear for 2m. Also been playing with magnetic loops for h.f.
73, Bill, G4GHB.
you absolutely know your facts, I have watched many of your videos, and tomorrow, I take my general exam. Hope there is no match on SWR...lol
Good luck with your test!
What a great presentation of such a complex subject. I can't praise it enough. What's missing for me, now, is how antenna tuners work. Obviously they counter the L and C reactances - well, "obviously" just means I assume so - but. . . I'll start over; Obviously antenna tuners reduce the reflective power coming back to my tuner, so it doesn't destroy my transceiver (and thankfully the transceiver is smart enough to shut itself down if I make a mistake). But, in listening to other people's videos and a little bit of reading, I've gained the impression that there's little else gained in using a tuner. Also something I listened to said that a tuner pushes the reflected power back toward the antenna and that it brings up the output signal, but I can't see how that's possible. Well, now I'm clearly in over my head, and I better head off to bed. Thanks again - I'll be back later to listen again. 73s - KC1DIW
Indeed, the antenna tuner catches the reflected power and sends it back toward the antenna. Some of that is radiated, and then some reflected back to the tuner again. So if the antenna is capacitive, the tuner will present an inductive reactance. Between the effective inductance and the effective reactance, there can be large circulating currents. These can create large I^2*R losses if the effective Q is high. Fortunately, for low values of SWR, they are not much of a problem for a tuner.
Another interesting and thought provoking video. Sometimes I think that we are all too hung up on VSWR, probably step one of the design should be an antenna that has the radiation pattern we want. Step two can be working out how to feed it...
Thanks!
Excellent!
great video. One of the best. What grade coaxial cable would be the best for use in HF and V/UHF respectively?
Just before 1pm on Field Day this year I connected my antenna analyzer to the coax, and I got about 1.32:1 SWR across the entire 20 meter band. Then I realized I was checking the SWR of my HF radio and not the antenna. :o My antenna is/was a Buddipole Deluxe configured for 20 meters at 19 feet, and my SWR was 1.42:1 at 14120 without the antenna tuner, better than 2:1 at the low end of the band and 2:1 at the high end of the band. With an antenna tuner the SWR dropped to 1.11:1.
Thank you for taking this easy to measure and say metric and providing understanding for giving cause to overly simplified usage of the ratio.
Too many discussions imply that swr reflects (ha) the end all for accomplishment of having an effective antenna system.. An increased risk to users of modern transceivers who are not into the science of antennas. Imposing to see even this quick look exposes just the beginnings of the inherent complexity.
One question, maybe noted elsewhere, would some of the reflected power recycle back from the transmitter and with portions eventually being added to initial transmit full power getting thru to being transmitted...and effectively reducing losses as expressed or is the this already contained in the measure? ...
Thanks again for all you are doing. Very beneficial for a 70 year old business major
My brain leaked out. I'm rekt.
Yipes.. Ok, so getting into this it seems I'll need to brush up on my math and science. Awesome!
Well now my brain feels like scrambled eggs, sure glad I totally understand swr now.
He reminds me of that guy pbs broadcasting. At the end of the night before they go off air they had this jack hymer the star gazer guy I thinks passed but that's who he reminds me of.
Yeah, that cleared everything up. I have to go get a drop slip.
Great explanation, Thanks you
73 de 7X2UV
Dave, thank you and a question...that you might have answered in this video ~07:03. Since earning my Tech ticket, the reason that SWR is always expressed as a positive ratio has eluded me. I've read many articles and viewed many videos trying to understand. Based on those experiences, I though that viewing this video would be "...one more attempt at futility." (Why my confusion? All the articles I've read (etc.) define SWR as something to the effect of (Max Voltage of Standing Wave) / (Min Voltage of the Standing Wave). Which would always be -1.0.) In fact, your video states that very formula. HOWEVER, in your comments around 07:03, you added--for the first time I'm aware of--the word "Peak". You said (approx) "Max PEAK Voltage/Min PEAK Voltage." Since the Min PEAK Voltage = Max PEAK Reflected Voltage...AH HA!...for the first time, ever, I hope I understand why SWR can be a ratio that's not -1.0. Which leads to my question...if you wish to address it...any idea(s) as to why there is such a dearth of clear, newbie-grade, explanations regarding SWR being a function of PEAK voltages (Standing and Reflected)? Granted, I'm probably the slow kid in this class...yet is it possible that everyone else in the Ham Radio world understood this relationship except me? To say the SWR ratio is unclearly explained in many, many, many outlets is a reflection only of the limitations of the English language to explain just how unclearly SWR is explained in many, many, many outlets. Your thoughts?
Rick, you can use peak RF voltages (always positive) or RMS RF voltages. In either event you come up with a positive number. Because the numerator is at least the forward voltage, divided by the forward voltage in the denominator, the ratio will be a minimum of 1. If the reflected voltage is added to the mix, the numerator grows. It is standard to state the SWR as a ratio (after all, that's what the R in SWR stands for), so it's stated as something (a numerator) to (meaning divided by) a denominator, normalized so that the denominator is one. I know that sounds roundabout, but that's why we say the SWR is 2:1 (pronounced two to one) instead of just 2. I hope that helps. 73, Dave
Darn, and there--for a moment--I thought I understood SWR. While I hope I'm OK with RMS ((1/2^1/2) * (A value, such as voltage))--regrets--I do not understand what values from Forward, Reflected, or Standing to put where in an RMS equation to produce an SWR. (FYI: Page 25.6 of the ARRL Handbook, 2015 edition, doesn't help much.) Would you consider an Ask Dave segment on the BASICS of computing an SWR? Not the formula (which you provided in the video above), but where to get the values to plug-into the formula? Many thanks!
I'll add it to the list of topics. 73
YIKES..... We use RG-213 50 ohm Cable in Australia.... I also use Belden 9913 50 ohm lo loss cable.... I haven't seen RG8 or RG8X for many many years... VK2LEE Lee
Great job, you put a lot of work in on this one and it is really appreciated. In one of your future views can you cover current phase angle, how it affects radiation and how to correct for it? Thanks for all your hard work. Allen N7LVS
I've not run into any material that properly looks at the phase difference between current and voltage along an antenna. I'd like to construct something because the usual animated GIFs wrongly assume the antenna is entirely reactive, with no radiation or ohmic resistance.
Few questions pls. Can a standard HAM SWR meter be used for VHF say from 80 MHz to 110 MHz? Does the SWR reading depend on power being fed? Will the reading be same for 5 watt to 50 watt with a dummy load of 50 ohms (required wattage taken care of). Should the 50 ohm cable length be multiples of 1/4 lambda for a 50 ohm GP antenna?
Yes. No. Should be. No--if the antenna is matched, the cable length doesn't matter.
Thanks a lot
Both L and C of antenna can be frequency-dependent. That's why it is possible that antenna have multiple resonant frequencies, or have no resonant F at all.
E.g. popular Long-Yagi design by DL6WU/VK5DJ goo.gl/xCHAEQ has 3 resonant frequencies. Some antennas have infinite number of resonant frequencies by it's design. E.g. Bow-Tie vibrator goo.gl/iNYJRQ has infinite number of harmonic resonances goo.gl/x645cX
Nice video and explains why my wanting a full wave antenna on the mobile would not work (I'd asked elsewhere and they couldn't remember why but that it would fail). I wanted it for length to try and get a resonant antenna on 480mhz with the elevated feed under it to match a similar length to the VHF hi with ground independent load (or at least the stainless whips).
So going by your theory here, since a full wavelength is around 60cm that would mean that a 90cm whip should work efficiently? How would it likely compare in efficiency to a 1/4 or 1/2 wave?
Thank you! KI7EDX
Fbs way I learned radiation resistance: (1) Resistance converts electrical energy to heat. (2) The ohmic resistance of an antenna heats the antenna. (3) The tadiation resistance of a antenna heats the rest of the universe.
Starting at 24:10 Also called SWR masking.
Near the end I thought (dangerous I've been told) about a dummy load power meter at the transmitter output going into a feedline and again using the same meter at the end of the feedline to see how lossy the line is. Probably should have done this with my new feedline to compare it with later readings. As it is, I can only afford electricians tape for the weekends that it's allowed up. Thanks de AG7MW
Good idea! I've not thought of putting power meters at each end of the cable. I'll have to give it a try.
Hello Sir, very well explained thank you.
Sir i was looking for videos related to Dual directional detector using transformer and attenuator it working and design explaination but none found in youtube. I will be very pleased if you make one video of it.
m.th-cam.com/video/ttvR3FG8AV0/w-d-xo.html
Dave in what order do i hook up my radio to amp then from amp to antenna tuner then swr/power meter then antenna ?
Can a current balun help some with the bad SWR when I can't get my antenna high enough?
Dave - I was going through one of your old videos (May 18/2016) on SWR and at about the seven minute mark you are referencing the highest and lowest points of the Cyan wave form. You refer to its highest point being 1.5 and its lowest point being 0.5, but on the active graph in your video it appears the lowest point is actually a constant 1.5. This would alter your calculation significantly - unless I'm wrong.
Michael VA6XMB
Sorry to have gotten it wrong.
Should the coax between the transmitter and swr meter be a certain length? Should the coax between the transmitter and antenna be a certain length?
Hi Dave, GREAT vid as usual... big fan of yours. Where did you get the spreadsheet? Is it available to us "newbies - technicians"? Will be working on my General class ASAP - HF has me hooked. Looking forward to DX'ing with you in 2018 from WA! 73
The spreadsheets are available at dcasler.com/2016/05/18/demystifying-swr-ask-dave-28/ in the last paragraph. They were really designed only to create the graphics, so they're nothing special.
Great, Thanks Dave!
"Antenna designers pay attention to this stuff." Well, the competent ones do anyway.
The company I worked for bought and tested 20 different antennas from commercial vendors. One marginally met its specs. The other 19 might as well have been coat hangers.
Only buy antennas from places with good reputations. Or build and test your own, which is a pain.
Yikes - I will watch this video 5/0.2 more times, at least... Thank you for not going too far in-depth! LOL
Someone said that inverted V lower the resistance and SWR a small amount. Is this true? Is so how much?
Hi, this video was amazing and eye-opening, what i want to know is - where do matching transformers come into the picture? They seem to be ignored in stuff relating to SWR but surely they matter?
A tuner can match a reactive load and make it look resistive to the transmitter. A transformer can't do that by itself.
@@davecasler Thanks for the reply, Is that because tuners contain inductance and capacitance?
Does duplexer play part of reactance and inductance ?.
I want to make a di-pole antenna. Where do I get the antenna wire and other materials?
I do not know if this is true or not and I do not even remember where I learned it at but is it true that a Longer antenna (on HF) is easier for a tuner to handle that a to short antenna?
Long or short is relative to the wavelength, which is different when the frequency is changed. The standard antenna is the dipole, which is one half wavelength long. At lower frequencies the dipole is longer, at higher frequencies the dipole is shorter.
his question is "whether it is easier for AT to work with "longer than resonant" than with "shorter than resonant" antenna. First, dependence of R+jX from physical length is dependent on type of antenna. For 1/2 dipole or 1L loop, longer antenna has higher R and +jX reactance (inductive), for 1L dipole and it's derivatives (bow-tie, cone antenna), reactance is opposite (-j for long, +j for short) and R peak it's maximum at resonant F, decreasing both for shorter and longer antenna.
Antenna tuner can work with any type of reactances, +j and -j, and transform R to any direction. For longer dipole (e.g. 80 +j20 instead 73 +j0) antenna tuner need just capacitance to deal with +j20. For shorter dipole (e.g. 60 -j20) tuner need inductance to deal with -j20. Building variable capacitor is much simplier than variable inductance. Dealing with R mismatch is even more hard. Simple lumped L network deal only with +-j, not with R. Dealing with R usually involves transformers, and they have fixed ratio
Dear Dave, circa 05:15, you say "...by definition, Standing Wave Ratio, or SWR, is the ratio of the peak voltage of the combined waveform divided by the combined waveform's minimum voltage. Note that the peak value of the combined waveform is two volts. And the minimum is zero volts peak...for a ratio of infinity." However, doesn't the animated Standing Wave illustration reach its minimum at MINUS two volts? Or, is min and max for SWR computed using absolute values? Or is there another "rule" regarding the way the "Minimum Voltage of the Combined Wave" is calculated? Many thanks for all your help! Rick
When the wave is damped all the way down to zero, the voltage is zero. Maybe it would be easier to understand as ratios of peaks.
Hello Dave I have always been under the impression that a 3/1 or lower is ok to transmit.not that I would normally accept over 2/1. What is your opinion on this please Dave as I have been working on some antennas for portable work and this question has come up a lot and I really value your opinion thanks in advance Dave de 2e0njk 73
In general, modern HF rigs will transmit into an antenna that shows less than 2 to 1 SWR. If it's greater than this, the antenna will start to reduce power to protect itself. Many modern radios come with antenna tuners that will tweak up an antenna system with an inherent SWR of three to one or less. In other words the antenna needs to be pretty near resonance already. The purpose of the tuner is just a touch that up. If you have a higher SWR, you can try a wide range tuner, like most of the aftermarket tuners. If you're dealing with QRP portable work, you might take with you a very small QRP antenna tuner.
You start out with the statement that SWR is one of the less important measures of antenna performance. Could you talk about measuring the more important ones? Also, I'd love to better understand characteristic impedence in the first place, and how it relates to actual total impedence and feed line loss.
Unfortunately, people use SWR because it's so easy to measure. There's also the percentage of power that's actually radiated, the beam pattern, etc. But the real measure is how much you like the antenna after having used it for awhile!
Dave I have 3 different meters, 2 MFJ .. 1 digital and one analog .. and a Diawa cross needled meter. I get totally different readings on all 3 of them for SWR and wattage ... my rig expert rarely agrees with any of them ... PLEASEEEEEEEEEEEEEEEEEEEEEE Dave tell me a brand of meter I can get that is really close to accurate ok .. if you could so a vid on all the different meters out there and tell us which one is the most accurate ... Thank you sir!!!!
I put my swr meter near tx. I want my tx to be happy. It thinks i have Swr 1:1 across the whole band. I am purposely using a 100 ft coax. I string a sloping endfed with 49-1transformer The antenna is 66ft and it slopes from 43ft to 6ft. I frequently hit the west coast from east coast and hit Italy, Finland, Slovenia. Also south into Caribbean. This is with a G90 at 20 watts cw mode. So I know the antenna is propagating. When i try a 50 ft coax, my propagation is not noticeably better but my swr increases as expected so my radio is not as happy. The antenna is put up in about 15 minutes and i take it down before i go to bed. I check swr through my radio’s analyzer and mfj 259. I have to wonder if maybe I should try a 75 ft coax. I think my antenna is using the longer coax as counterpoise. I tried adding counterpoise and it did not affect swr at all. I know my swr at antenna cant be that good as it appears but the transceiver thinks its great. So I don’t have any counterpoise.
Also, it thinks it’s 1.1 on 40 and 20m. And less than 2.4 on many bands. It has a built in tuner but i never use it.
Love your video. It was very interesting. Thanks
Thank you. I can't tell you how many times I've had arguments about SWR. I've always said 2:1 or lower is Ok. Let me know if you think this is correct. Thanks.
Yes, usually
You said that it is rare to have an antenna with 1-1. All My antennas are resonant on the band they are used on. It can take a long time to actually get the antenna to the 1-1 where no SWR is shown. VK2LEE Lee
A 1 to 1 SWR means that the antenna is not only resonant, but the input impedance is exactly 50 ohms. That's pretty rare. But if you can get it there, more power to you, literally.
@@davecasler I shouldn't say every antenna is 1-1 but very close , but I am finding many new hams trying to use one antenna for all bands or many bands... with terrible results.... Excellent video DAVE...VK2LEE Lee
Do you make any of your spreadsheets available to experimenters?
You can find the spreadsheets link here: dcasler.com/2016/05/18/demystifying-swr-ask-dave-28/. This will allow you to download a zip file. The spreadsheets are in Libre Office format. They were primarily designed to create graphics for the video, so I can't say much for their accuracy if the values are changed substantially. Good luck!
Wait just a single minute... you say that the resonance feedback only happen on the transmitting frequency??? what happen with the adjacent harmonic frequencies! the double, and triple..
Transmission lines are passive systems and as such operate only at the input frequency. Without active (non-linear) components, they are incapable of creating frequencies not already present. If harmonics are input, then they can be filtered also.
thank you sir
Greetings David. I made some calculations and if for example, i have (50 + 45j), maybe 1.3 swr, the question is, what is a safe reactance for a transmitter? Because the ideal would be (50 + j0 )but that is not the reality. I know that reactances can have dangerous voltages. A (0 , 50j) theoretically can have 50 ohms but not radiation resistance. I believe (47, 12j), you know 12j or less. I would like your opinion.
I'm not following your question. In general, 50 ohms resistive is the ideal load. As a rule of thumb, any SWR less than 2:1 is probably acceptable, but you are correct that the more resistive it is, the better.
Thanks for your answer. I agree with you. I know it's impossible to get a perfect antenna. By the way great videos. I am extra since 25 years and I always see your videos to maintain fresh my brain. And I learned new things. So thank you for your good work with your videos.
It depends on transmitter impedance & reactance (including it's antenna tuner). If transmitter has fixed impedance (let say 50 +j0), than any reactance will increase SWR, any R different from 50 will increase SWR. But if transmitter has tuner, which consist of 2 parts: reactance compensator and resistance transformer, than it can have SWR=1 with any complex antenna impedance. If antenna has +j reactance (inductive component is high), than antenna tuner with extra capacitance will compensate reactances. If antenna has R=25, then 2:1 transformer will match impedance and you will achieve SWR=1. In practice, tuner perfomance is limited by the fact that impedance of cables is fixed (e.g. 50 +j0) and antenna tuner must be placed near antenna, not transmitter. Another bottlneck of working with very low R is higher ohmic losses, with 2:1 transformer you decrease Voltage and increase Current twice. Twice current is 4x heat losses. Bottleneck of high R is high voltage and air ionization (possible arc).
Why is it so many online sources use 2pi * f instead of omega (w)? Or in other words, why do they use frequency instead of angular frequency?
I think most people think in Hertz rather than angular velocity.