The Truth about SWR: Debunking the Myths and Misunderstandings 

Nice job Michael! Made me think past the SWR standards. I would really like a video taking this a little farther using a RigExpert AA-650 Zoom or similar and talk about what the optimum X,Z,R numbers on the meter would be to strive for when tuning up an antenna.

Another thing to Keep In Mind is that 1 S-Unit is 6db so 1/2 S-Unit is 3db, and in most cases 1 S-Unit signal loss at the other end will not be noticed UNLESS your close to the noise floor in Weak Signal Conditions where your signal could be lost in the noise. I have close to half a century as a ham and made my living as a radio tech, and I don't let lossy bands with high SWR and an Antenna Tuner prevent me from making a contact. 73 mike 🍺🍻

Great explanation. I've explained this to many folks over the years, but you crystalized it very well for a short video. Generally speaking, most hams understand SWR as well as they understand grounding and bonding - almost nill

Thank you so much for this video! I have been preaching this gospel for years and now I finally have a terrific summary that I can just point people at! 73 de AA5SA

Good information. Well presented. Now I have to get to work and figure this out. ✌✌

This information is just gold. Thanks for it!

Little surprised you talked about coax as if it is the only transmission line (no mention of balanced line). Also surprised to see the use of "Db". When presenting technical stuff, wrong units serve as a distraction. Good discussion on reflected power. 👍

Thank you for this video. Studying for my first license and SWR has always thrown me off the hook.

Interesting and most helpful. Thank you Michael and DX Engineering! W5JCS

I find the best VSWR is when you connect a 50Ohm lump of carbon across the antenna, but i don't seem to hear much. My ERP is very bad as well. But i'll live with the great VSWR 🙂

There is another large gorilla in the room, impedance presented to the transmitter. Transmitter power amplifiers are designed for optimum IMD performance and efficiency at a specific load resistance. Ham equipment sacrifices transmit IMG performance for oomph out the antenna. Still, varying that load resistance from 50 ohms to a lower impedance means the output waveform will flattop at a lower current than the transmitter tries to supply. The waveform distorts. Other hams complain. If the load resistance is higher than the design load the PA will go into voltage saturation at a lower instantaneous voltage. That gives more IMD and more complaints from hams on adjacent frequencies. Both cases can also reduce how well receivers can decode most of your modern digital waveforms. The only cure is to reduce transmitter power so BOTH instantaneous voltage peaks and instantaneous current peaks are less than the design levels. In effect this is another "loss" in the over all system performance. Of course, remember that a 1 dB (about 25%) power loss is usually not going to make a difference in your ability to communicate. But that is yet another aspect of the overall system design to consider. "What things are worth developing intestinal upset over?" {^_-} Joanne/The design is not over until you have looked for ALL the problems/ W6MKU

Very informative and well done video.

Oh my, now we’re tuning coax! Tuners belong at the antenna, not the transmitter. Are you putting your half-wave antenna baluns at the transmitter, too? All you’re doing is creating more loss in power by bouncing the impedance of the 50 ohm cable on both ends. Phase would only be affected by the output coil, but what you’re adjusting it for is to wipe out the reactance. The SWR or reflected power from the forward coupler metering circuit is not looking at phase, it’s looking at energy flowing in a particular direction. I need a Tylenol. This is why resonant antennas work best folks. This is why the DXCommander and similar resonant antennas work well. Keeping the load as close to 50 ohms and minimal reactance is the key. And when it isn’t, matching/tuning it at the antenna will provide the most effective results, not the tuner in the shack. All that reflected power coming back into the shack is really getting lost in the coax, your output tuning network and final amplifier transistors or tubes, and not slingshotting back out into the antenna. Again, use your basic training; place an ammeter on the antenna and calculate your results. Or… Place a remote tuner at the feed point and tune/adjust for maximum power from the shack. 😊

For many years I had no SWR meter and just tuned for maximum r.f. out as shown on an r.f. pickup meter at the aerial, long wire coming into the shack or a vertical for outdoor operating. A doublet with torch bulbs in the twin feeder. When I made a resistive SWR meter then checked as the SWR went down the r.f. out went up. I did notice the lowest SWR reading was not quite maximum r.f. out but only the very slightest difference. I aim for below 1.5:1 if possible. I have short lengths of mini 8 coax of 25 feet to 20m to 10m attic dipoles and 50 feet to an outdoor inverted vee for 60m. QRP with nothing above 5 Watts. G4GHB

Ciao Michael, complimenti ottima spiegazione, ti faccio un appunto, nelle slide dove si vede la radio, la linea di trasmissione e l'antenna, il termine decibell e scritto in modo sbagliato! Hai scritto Db ma si scrive "dB" perché è l'acronimo di deci-Bell "Bell e il nome del fisico che l'ha inventato" per quanto riguarda il Rosmetro o SWR meter, in stazione sono pienamente d'accordo che leggerà più o meno correttamente i valori di SWR solo alle basse frequenze, diciamo le HF fino a 30MHz, poi salendo di frequenza in VHF e soppratutto in UHF e quasi inutile se non si utilizza un cavo veramente corto e a bassa attenuazione! Anche in condizione di adattamento di impedenza tra Tx e antenna, se l'attenuazione e elevata, si rischia leggere valori di SWR talmente bassi da non distinguere se l'antenna funziona oppure e scollegata o in cortorcuito, quindi pensare di leggere il vero valore di SWR in shak a frequenze nell'ordine dei 450MHz e una chimera, ma questo vale non solo per il SWR meter, ma anche per un Bird, o un Nano VNA dove si vedrà una traccia più ondulata a basso valore di SWR! Quello che hai spiegato lo si trova anche sul sito della BirdRF nelle application notes, e si chiama "Cable Masking Effect" Ti seguo con interesse, un caro saluto 73 Pier Francesco Grazioli

Good stuff 👍

I have tried to explain this to some people so much that I just gave up

That would explain why I have an SWR of 1.5 with the radio turned all the way down. Then as I turn up the output, SWR also goes up.

Using RG-8X coax with my 20w G90 seems to work just fine, but if you have a more powerful base station and want to support a wide range of frequencies, then getting good coax is a definite must.

Excellent insight. Thank you.

@DXEngineering I would love to see a presentation about a 130 ft doublet fed with 1" twinlead/ladder line.

Thank you, this is helpful. If you are receiving only, and not transmitting, is the SWR reading at the feed end a good indication of the antenna’s resonant frequency? I use some SDR dongles for receiving signals from passing weather satellites and have tuned the antennas based on the SWR numbers. Is that a correct method?

Thanks Mike. Good presentation. Is that a Hallicrafters SX110 on the top shelf of the bookshelf behind you,?

XE2ZZ Good Info.

If power isn't reflected and absorbed by the transmitter, why are finals damaged by having a high SWR? My personal take on feeder losses is that if you have a loss anywhere near 3dB you need to give your head a wobble and give up - especially at HF.

Well that was entertaining and educational! Explain how "grounding" has NOTHING to do with achieving a low SWR - AND - how "earth grounded antennas" are both dangerous and illegal according to the National Electric Code. KD8EFQ/73

Old operator here which is more accurate? Quality swr meter or antenna anylizer ?? Havent used the anilyzers yet always trusted calibbrated swr meters Or is plotting meter responses on graphs ( old school) just as accurate?

Good Video Mike! 73 ghw

Interesting that you don't mention CMC. CMC and reflected signals is like Clark Kent and Superman. You never see the two of them mentioned on a YT video at the same time.

Please explain how reflected power eventually gets radiated. Before you do, place an RF ammeter at the feed point of the antenna, as well as a bridge or VNA to determine the exact resistance. Then using the standard formula of (I x I x R) current times current times resistance, and then tell us what that calculates out to. Now, use your VNA or impedance bridge and measure the impedance of your transmitter’s output. This would require activating the antenna switching relay to actually do so, but in most cases you’ll find the output if a transmitter, or amplifier, is lower than 50 ohms, which will create more power loss as a terminator. But let’s assume it’s 50 ohms for easier calculation and our transmitter is 100 watts. A coax loss of 3db at the antenna that causes a 10% loss of power means 45 watts is flowing forward into the antenna and 5 watts gets sent back to the radio. If what you’re saying is that this power is then reflected back from the radio to the antenna, the power at the radio is now 2.5 watts and by the time it would presumably get back to the antenna, it’s now 1.25 watts. So, it is getting wasted, and nothing of any consideration would be sent back to the antenna. Now, if you assume the load is actually much lower, like in the 5-10 ohm impedance, then even less power would be sent back to the antenna. Now, I haven’t even began to discuss the phase of the forward and reflected waves, but length DOES play a role here, where it could be possible that any amount of power that is reflected back to the radio, or the antenna from the radio, could be phase cancelled or attenuated. Simply put, reflected power is mostly lost power and very unlikely to make round trips and find its way onto the antenna.

Nope,Dope. Length matters.

ive got my swr down to 1.3 but when i talk into the microphone it goes up to 3 is that bad ?

@10:22 . That statement is not entirely corect or a list for same type of ampliers use in transmiter. Reflected power do reflect back from transmiter. It will be partially absorb by power amplifer. I am doing some power handling on components in the company that I work for, and let me tell you one thing. If the load have savire mismuch and the power is reflected back to the source with out much loss in transmission line, the power will be absor it as it have own load characterystics. In such case the output power may drop due to prezents of signal in both direction - forward and reverse. Remedy is to use additional attenuation on the transmision line with penaly of loss of power, or use some isolator or circulator to redirect reflected power to dummy load. Some amplifer have aleady build in such protection so they might not effected. Just be aware that you may see something like that.

Apparently we don't even need SWR meters. Just run it.

It's not very good, it cancelled a lot of it's trains like SWT. No way as good as SW section of BRSR.

Michael THANKUOU ❤🎉🎉 & DXE Thankyou, 73s 9V1KM KK7QGL SINGAPORE