From an American trucker, I'd like to say thank you for the simplified ways to get my swr figured out . I will be watching out for any updates from your channel.

I wish you made this 16 years ago hahah. I acquired my first cb radio and was so misled and fear-mongered about SWR and blowing up my radio that i barely used the thing. I was not in amateur radio at the time and youtube wasnt all that flooded with trustworthy information at the time. I cant tell how many forums and articles i read that touched on this topic and i was still lost. Thanks for removing the mystery of radio and providing accurate information!

When I was into CB here in the US back in the 90's, I was told coax had to be cut in 3 foot intervals due to SWR. I didn't know any better, so when I bought my base antenna coax, it was 51 feet long. Fast forward to 2020 when I got my ham license, I'm thinking back to this coax and the 3 foot interval and it doesn't make sense, and I can't believe the malarkey that people I trusted spewed. Thanks, Cal. All the best. Cheers. KO4QOA

Wow been on and off CB for 45 years, and all I've ever heard is it's all about the length.of your coax, and it's never been a problem with me anyway.but just at the end of your video you said,if I got some extra wire I would coil it up anyway . which has only just clicked that you coil up the ARIEL, bottom ,middle or its on the top , so the moral of the story is it don't matter.thank you very much . DX COMMANDER.ALAN IN LUTON 💯👍

I can’t even begin to imagine what was wrong with my setup in the 70’s. it wasn’t grounded, the coax (RG8) was cut to length from the 60’ high wilson shooting star (4v 4h elements) antenna to the radio in the basement. the antenna was simply adjusted to the measurements in the instructions. i did have an archer swr meter but that’s nothing like having a rigexpert analyzer. I do remember getting shocked all the time if my hand was on the mic and I brushed up against the amp. I was just thrilled that my parents even allowed this monstrosity to be attached to the side of the house.

It is NOT the length of your coax that matters….. it is how you use it! 😂

The correct length of coax is the distance from the antenna to the radio. Period.

New to CB radio. Installed one in my vehicle and then a base in the home. This helped me understand SWR and answered a lot of questions I didn’t know to ask.

Fantastic as always Callum! 73

Your videos are not only informative but entertaining as well. Sometimes I get lost for hours watching them and when I do I always learn things. Thanks for doing what you do.

About 30 years back I was on the CB an moving over to ham. I was listening to some girl speaking about looking at two CB radios. An saying we got the other one as the swr was lower. I did try and explain how to measure it. And to re cal the forward 1st. It was like speaking to a goldfish. Telling her it looks lower as the output power is lower.

Satisfying to watch., You're a master. In 10 minutes painted a picture that taken me years to wrap my head around..

So in 2018 my wife passed me down from the loft my ham international CB radio from the 1970s and I switched it on and it bloomin well worked! Put a vertical up and there was two people on in our area. All I was interested in was DX so I went on SSB and got a few contacts into Italy. A really nice lady used to come and chat with us local guys and she went on about how I should get my licence. . . So I did. I was watching your channel as well and thought that it was a natural progression. What a difference. . . I am so pleased with the hobby and the fun that I am having. I don't know why CB is a touchy subject on the ham radio as it was the first form of social media for us before the internet. I was actually taken to the crew room of our life boat station when I casually mentioned that I was interested in taking the exam and the guy who I was introduced to nearly collapsed when I told him that I was going on 11meters SSB. . . . He said that I would have to go to the local club for 3 years before being put through the course, so I did it with Essex ham. Ha Ha. Keep the videos coming. Kind regards Simon.

There’s so many funny “rules and guidelines” when it comes to swr, feedlines and power. But one thing is definitely true and that’s if you let the smoke out, something stops working. It’s all about the smoke. 😂😂😂 KZ5Y

Fantastic information and fantastic video

My favorite YT channel. Cal, you are the man! Waving from my tech bench. 73👋🏻

You’ve cleared up a few things on antennas, SWR and coax length! Thank you from VE3NMW.

First time that I have seen some of this info. Helped me realize that I was using the WRONG ANTENNA which gave me too high of SWR. The correct antenna has just been ordered.

Another great video. Cheers Cal

Hahaha….I remember something about this argument for more than 40 years!!! Laughed then, and still laughing about it. As an RF expert (now retired), it simply and easily ID’s those that don’t have a fundamental understanding of…. Well, I don’t want to pour any salt on wounds, but you did a very nice job of letting the air out of a few balloons. And yes, I had 10 or 12 extra feet of RG-8 coiled up on the floor by the window where it went outside to the antenna. One friend just couldn’t stand that. Hahahaha. Good job!!! …as usual…

Brings to mind the phrase "the complex conjugate" when matching 50 ohm rigs to an antenna that is anything but a 50 ohm antenna, I have been doing this for many years.

Thank you for explaining it in simple terms

I agree with you. I have always tried to keep my coax runs as short as possible. Once you know loss per 100 ft, its easy to figure out your line losses. If the length of your coax affect your swr then something is wrong somewhere in the system and it's most likely your antenna. Nice explanation Callum 73's Gary KF6EWO

Fantastic video as always .

Good advice Cal, thanks for the vids!

Keep providing great antennas and great information. You are and invaluable service to the whole radio community (cb included) thanks Callum

Half of the fun is experimenting. Thanks Callum!

Great video. In my younger days, on CB, everyone said you have to use 11 feet of coax on a 102 inch whip mobile antenna for everything to work right. Over a short period of time I figured out that was baloney! Thank you Cal! 73s ND4A

Thank you. I feel better about shorting the one in my truck. Built a homemade pvc/copper ground plane for the garage from mower junky to match 38lsb. Now I have a kenwood 490 and can go all over the place. The auto tuner is Awsome for that. Even learning a bit about fm on 26.805.

Logical.... Thank for the bit of wisdom appreciate it.

Depends if you want a voltage peak or current peak on the end of your coax. Half wave or full wave determines that.

Trying to explain this to a friend of mine who’s a trucker has been absolutely maddening 😂. I sent him this video, but I’m fighting his 40 years of “experience”. This myth is very firmly rooted in many of the CB “technicians” minds.

Hi Callum,,Agree totally, that said with coax becoming an impedance transformer with an antenna feedpoint mismatch, the radio will see different impedances with different lengths, you spoke about half wave lengths repeating feedpoint impedance perhaps another video on feedline impedance transforming to completely eliminate the myths 👍

Used the ARRL antenna book to build a magmount that way around '77. The vertical is a hand wound helical about 5' tall that comes apart midway for storage. And since rare earth magnets weren't available, used two aircraft radar magnetron magnets to hold it down. Leave those in place for 24 hours and it takes both hands to unstick them. All hand tuned, no "stinger" necessary and the swr meter sits there and says "what's swr?".

Lol, Cal. It reminds me of the 70,s when my oldest friend had a CB shop doing literally thousands of installs. Most people dont understand characteristic impedence any better now. Most vertical antennas have a characteristic impedence of about 37 ohms, not 50 ohms, so around a SWR of about 1.2. The mythical 18 foot coax came about from the Ford LTD sized land yatchs needing about that much coax to go from the radio under the dash to the 102in whip on the rear bumper. Many many times someone would install antennas in horrible places, like dual center loaded CB antennas behind the cab of a pickup or on the roof gutters on a Pinto, so either too close to the cab. Or too close together. So we would trim the coax to make the radio see a lower SWR. As you go along the traveling wave you can pick a length using the published velocity factor that will transform the impedence seen by the radio. IE: a 75 ohm antenna can be tuned to 50 ohms by using a 1/4 wave of 75 ohm. A transmission line that is terminated in some impedence Zl, that is different from the characteristic impedence Z0 will result in a wave being reflected from the termination back to the source. At the input to the line the reflected voltage adds to the incident voltage and the reflected current subtracts (because the wave is traveling in the opposite direction) from the incident current. The result is that the input impedence of the line (ratio of voltage to current) differs from the the characteristic impedence and for a line of length L is determined by a formula i cant post using my phone lol. Look up Quarter Wave Impedence Transformer in Wikipedia. There is a good explanation and the formula. You absolutely can transform the characteristic impedence of the line to match the input impedence of the system. Does it make a difference? Not really in this instance, the wave still sees an impedence mismatch at the 37 ohm antenna and sends energy bouncing back to the input, it just bounces back at a phase angle that lets the radio see closer to 50 ohms. Lets all remember that the 50 ohm standard was chosen as a compromise between the 37 ohms of an unbalanced vertical antenna and the roughly 73 ohms of a resonant dipole at 1/2 wave above ground.

What a Brilliantly 'Simple' vidclip .... Loved it.... Like the way that you 'Call a Spade a F.... Shovel ', No messing around ..... :-) :-) :-) Best to You and Yours and All 'Radio Hacks' out there.... Cheers from ChCh, NZ WR 2451 / KK 2451

I don't understand the animosity to CB with some radio hams, radio is radio, it's all good fun. I used your calculator to tune my Signature 9, I built it and cut according to the chart, but I wanted the CW end of the bands, I adjusted the length the calculator gave me and it was spot on the desired frequency, saved me hours of mucking about with an analyser and side cutters.

Like yourself Callum I never could understand why operators wanted the one to one swr like it made all the difference...well explained and 100% correct....Top mam 73s Callum

All you say makes perfect sense and answers a lot of my questions I had over the years that no one had any real answers too. It's about time someone made a video like this, Thanks. The only thing and you mentioned it was the figure eight. I was always told never to coil the coax. Like you say it's called a dirty ballon. Q/ Can you have to much coil aka dirty ballon? How much coax is to much coax? and how much damage does the sun do to the coax if you have lets say a 20mtr tripod? I just searched for Figure Eight vs Coiling Coax using many types of keywords and found nothing about the coiled coax being called a dirty ballon and why or why not to coil or figure eigth the coax... Might be another great video you could make explaining it to people like me :) !

"I can't drink your poison", that's great. You talk about CB, I guess it applies to any transmision line on any band.

You sounded like the much needed SWR-therapist for CB-guys. I know my uncle was also very picky about the channels to be used because the SWR was good there... 73!

Mate, keep going on with references and information to CB. Afterall, I think most would have come from CB roots and interests and if it inspires others to further their interests then it can only be a good thing for the hobby. I for one play on the cretin's and Free band and enjoy it immensely and I have to say from my experience that it is nothing like it was in the 70-90's. But I am gathering up my knowledge to go sit my STD license soon. There's an awful lot of Hams that get on the "Cretins Band, Childrens Band, Chickens Band" as its shouted out behind the scenes and don't or won't admit to it but they do. BTW, you have reinforced my perception of SWR and feed lines and antenna theory not just this video, but all the other videos you do and hang out waiting for your future videos. It's great that some of the horseshit out there is being called out for what it is. Now if I can only educate a mate of mine, I'd be happy, but I don't think there is any changing some people.

Another great video Callum 😊your such a good teacher, keep up the good work

Thank's my friend.James from Greece.

Excellent video

I was found the correct length was enough to reach from the radio to the antenna plus a bit extra to make in easier to connect

That's funny because I got a coax a week ago just got into CB's and then my coax broke in my door (was just testing everything) I ended up pinching and breaking it and then a friend tested it and said I had horrible swr and I seen the break and just recrimped my lines, I ended up hooking it back up and noone knew I shortened it to like 8.5 foot. He checked my swr again and boom it was awsome 1.1 -1.2 and everyone said it shouldn't work after I fixed it but it works great lol 😄

CB'ers can also use impedance matchers we HF hams use. CB is between 10 and 12m.

Thank you by the way love ❤️ all you explain!

A mistake I've seen CB'ers make is that they get hyper worried about SWR. As you've stated, there's not much actual difference in performance between a 1:1 SWR and a 2:1 SWR. I've seen people think that there's a huge power gain if they get a 1.2:1 SWR down to 1:1. That they're gaining a ton of performance. I've seen people change out a 50 foot length of RG-8 or RG-213 for a lossy 100 foot length of RG-58 because then their SWR reads 1:1. With only 4 watts of transmit power they're losing performance both transmitting and receiving. Using the lowest loss and shortest run of coax and tuning the antenna for a reasonable SWR is best. Thanks for your video! 73 de AF7FP.

I used to feed it with odd multiples of electrical quarter wave. For the simple reason to have a low voltage feed point limiting arcs. High voltage nodes were aproximately detected with a small neon light on a stick😀 That was many many years ago 😂

The only time I take coax length into account is when I'm using multiple antennas and I'm taking phase into account. Or if I want to play around with circular polarisation with a cross Yagi. I do prefer to use ladder feed on base antennas because of the loss efficiency. Plus of course I can make a non resonant antenna outperform a resonant antenna ;-)

Bloody brilliant!

Well done.

The amount of arguments i've had on this point! One thing that can exacerbate it is if someone has a problem with common mode currents on the outside of the coax, It can upset swr measurements, And as common mode currents ARE on the outside of the braid they are not involved with the velocity factor. So you get the illusion that the coax length thing is true. Good explanation by the way, Can you imagine setting up a top band antenna in a vehicle if you had to use a half wave of coax, velocity factored or not!!! 73 de Mark

There's a lot of people out there tricking themselves, and their SWR meters with a pair of wire cutters and a roll of coax!

Following on from your comment about a dirty balun using the excess coax. If you use a length of coax that is an odd number of quarter wavelengths (adjusted for velocity factor), then this will also act as a really good attenuator for common mode current running on the outside of the coax. I wish I had known this when I was a CB operator. One advantage of becoming a licensed amateur radio operator is that you get to learn all this stuff through the courses for the exam, and the support and knowledge of the guys in the local radio club. Keep up the good work, Callum. I look forward to your nets on Fridays. 73, David - M0NMI.

Another thing I forgot to mention, the wearecb site text does not state that you might have trouble achieving a good SWR, it states good SWR 'readings'. This is because common mode current can affect the reading, resulting in an erroneous measurement.

Velocity factor vasmoshity factor. Thanks, well done.

Most cb antenna, where the vehicle has a fiber glass body, must use the coax shield as part of the antenna's radiating element, like one side of a center fed dipole for example. If the vehicle body is metal, then the metal body would provide the driven element something to work against, and coax length would be irrelevant . If one could drive around with a ground plane antenna, like the example in the video, coax length would also be irrelevant. Thanks for sharing.

I was told this in the 80s, cut my coax in full and half wave lengths and have been laughing ever since.

This myth about coax length also circulated in America. Some people even crammed all that coax into their cars. I was working in a Radio Shack back then and amazed the clientele with soldered connections rather than just twisting the wires together!

My last real CB setup had a quarter wave antenna centered on top of a commercial van. The antenna and coax were tuned with a $25 000 Vector Voltmeter I happened to have at work. A stock JC penny 40 channel SSB radio could talk from Oklahoma City to Oslo like it was down the block. Now, you can get a vector analyzer for $60. There's no excuse for running around with a miss matched rig and antenna.

If the swr changes with different coax length, that means the shield of that coax is hot with RF and in fact radiating. Those who direct feed dipoles with no balun may experience this, or shoddy designs of verticals may experience this. Callum is spot on about coax length in a properly working antenna system. The length of the line shouldn't matter except excess adds loss.

Dealing with plotted curves works the same way in photography. Moving the gray scale around to achieve the properly printed print on paper. Subject matter is another entirely different matter. The way you explain it hit a DUH nerve and becomes so simple. The confusion and terror has wafted away like a fart in fast sports car.

Back in my CB days (just before the FCC gave up on it) I was fortunate to have a couple of local hams that helped with fixing up the radio I had at the time (23 channel Cobra 138 with Siltronix vfo, AND had an extra crystal board for 10 meters!! Got it dirt cheap, too!), and giving advice on radio in general (like if you think you NEED a linear, put your antenna up another 40 feet) Now that I'm a ham, I can't seem to find ANY "friendly hams" to help (local, anyway, nearest club is 40 miles away and haven't contacted their contact after WEEKS) and the ham bands are about as bad as CB now!!! Have a radio and antenna (gave up looking for radios online, everyone seems to want almost as much for their junk as a NEW radio, got a closet full of them as proof, so I bought new) just need to get the antenna up and the radio on the air!! Great video!! DE KE8NFK

I’ve always thought that 18 foot coax idea was bunk. After doing a lot of research into shortwave radio and scanners, and building antennas for them, I was always scratching my head at the whole 18 foot thing. It just didn’t make any sense. Now I know. Thanks for clearing that up. And yes, ALWAYS use the best quality coax intended for your application. I know that good coax is very expensive, but it is what it is.

I've been looking at this for a few years. The problem with mobile antennas is that they are using the vehicle for a counter poise. If it's a poor ground, the outer shielding of the coax will be the counter poise. Cutting it short or coiling it up will change the value of that counter poise. KO4UGN

in the 90s I also heard many theories on conductive but non-magnetic antennas and supports, I saw the coax cable cut for cb in multiples of half a wave, calculated on channel 20, also calculating the speed factor of the cable and a speed of light of 198,000 Kmh why not in free space where it is calculated at 300K, all for a CB with 4W, anyway RG213 is the minimum to use. Thank you🙂

Very interessing. Félicitations.

I would like to add for the CB'ists that when you run a really long way to your antenna, RG58 is better than RG213, as it gives you a much lower SWR at your transceivers side 😂 - and bringing the antenna down right above ground gives even a better SWR (and saves the worms from getting a cold) 😜 Oh, yes, thinking of all those myths takes me back to my early 90s CB years. Thank you for the memories! 😊

@DXCommander Thanks for all your videos, I've had the 🔔 for some time now. I've just sent you an email about your SWR calculator, I know you prefer to keep comments on here, but it's not one I could post because of the algorithm!

Excellent and helpful video. I hear so many myths associated with this subject.

I run 9ft or 12 ft of rg213 coax works good on a t680 semi truck just put right antenna on truck and get good swr and range using a rigexpert antenna analyzer i like ones with white center insulator of the pl259 connector never liked the purple or yellow one cause was told white ones handle more heat to not melt when running high power through it

I called President and asked them about cable length and was told it does not matter. I ordered a RigExpert AA650 Zoom and a bunch of antennas and cables and will do my own testing. What is right is what works. I have solar panels on my van roof and need to find out if they are affecting my antennas also.

Also - how often are antennas actually the true 50 ohms at resonance in the real world?, ie how high above ground is the antenna?, is it close to other wires? what about that 40 feet of roof gutter sitting less than 1/2 wavelength away underneath the antenna etc . . . . Anyways - all good stuff Cal! Another great video...... Current project here is a coax fed 3 wavelength per side 10 meter Vee beam looking northeast towards Europe, the Vee is up about 40 feet (the legs of which are each approx 100 feet long)..... It is un-terminated so am getting good results also in reverse to the south-west... So far is good results on 10/12/15 meters, though the ups and downs in propagation keep it more than interesting, not to mention the local snow and ice storms in the midst of the current project hihi ! Is nice to have one antenna with gain for more than one band and two directions. WWV on 25 MHz is super loud on this antenna

You are spot on. BUT, I wanna see you play those drums!!

Thank you

Coax length is very important it must be at least long enough to reach between the radio and the antenna.😊

A half wave end fed antenna with a 49:1 unun without a counterpoise andr RF choke will use the coax shield as the other half of the antenna and thus the length of the coax will affect the SWR.

I got into 11 meter SSB, even had a four element Quad. Finally transitioned to amateur radio about 2010. 73.WW5MB

Thanks for your videos,… always watching you from Kentucky “ The Bluegrass State “ my friend. Great content. Thanks for the info on the coaxial cable. My question on Home coax and connections to The Base Antenna is . I purchased a connector for my Base Antenna set-up and it Allows me to set up a ground wire to the ground on the house with a 8 foot copper rod going into the Earth. Will this make a Big Difference in listening and Transmissions ? Thank you 🙏

I've been enjoying radio of many forms for nearly 3 decades. When conditions are right, I have more fun on CB. Amateur has exponentially more things to do and frequencies to enjoy, but I just have more fun on 11 meter - when conditions are right.

Hello, speaking of RFID 13,56 MHz, dose the coax length matter? I mean I understand that that long means more resistance but dose it effect the resonant frequency on the Antenna?

Good video, back in the 80s we didnt care about the length of the Coax, it was more important to get the SWR down as far as we could, now i dont live in the Uk have moved to Australia they are anal about Coax and how long it should be, i still go on about the SWR and coax is as long as it needs to be to set up a base station, and as long as the SWR is as low as it can go thats good enough for me. Can you do a video on the Clarifier, i call them 12 O'clock here as they will not use to clarifier to tune in a station that may be off frequency, we know not all test equipment is not equal and there is going to be a slight difference, you go out for a radio check and all you get back is, Your Off Frequency, and thats it, instead of saying drop down a couple and getting the other station to get back on they ignore you. Just subscribed and given you a big thumbs up from this expat 60+ yr old Teddy Boy...

Hi Callum, it struck me today the best argument about not cutting coax to length. To anybody new reading here, think about this! An SWR meter is not an isolator. The aerial side is not somehow independent of the input side. It is a fancy connector with a meter just like any coax coupler making two cables into one. Cutting a cable just adds to the other one through the meter. A waste of time cutting it. As we amateurs say, there's no point in trimming coax inch by inch to a specific length. G4GHB.

explained like a boss

Wonder what they’d do with a doublet?

Enjoy your radio and get on the air that's all that's matters. Have a good day Callum Motters M7TRS 73 👍🏻

The millions of conversations I've had explaining to people that what they say is some kind of nonsense would have been simpler had I known there was such a myth! Thanks for making me realize where it came from.

Another great educational video. Thanks!!

I noticed on Houston METRO buses there seemed to be some sort of strap dragging on the pavement of the buses. I had to ask. They said they had to ground the buses due to the buildup of static electricity. I wonder if those kinds of straps would work on cans/trucks going mobile? Or hooking up grand wires along the ground while stationary like one adds to a Wolf River Coil antenna?

I wonder how many miles of cable was bought thanks to that myth? Have to put my hand up and say that I believed it in my early days until I studied for the RAE.

Good advice as always Call. I extended my first mobile CB antenna with a paperclip to get the SWR right, as I got the USA on the low power (4 Watts I think) that my CB had it worked well! Coax is one of the most misunderstood parts of our radio set up. As an M7 I have to work at getting everything as efficient as possible, something the Tech holders in the States miss out on, as they can just turn up the power to overcome any losses in there set up. 73 Jim M7BXT

I changed the standing wave and the bandwidth of an antenna for a CB radio operator. I unsecrewsed his 259cm long ¼ wave whip and screw in a 259cm long ¼ length of copper tube. The tube is 25mm thick. It made the operator able to transmit from 26Mhz to 28.505Mhz on one antenna, all of the range under 2:1. The radio could have probably transmitted higher than the 28.505Mhz under 2:1. But the operator said he was not allowed to transmit above 28.5Mhz on 10 metre bad. But, interestingly, 26Mhz to 26.960Mhz and 27.41Mhz to 27.60125Mhz do not seem to bother him to use them. Only 26.965Mhz to 27.405Mhz and 27.60125Mhz to 27.99125Mhz are legal in this region. Why would he not go from 28.5Mhz to 30Mhz?

Long ago I found length of coax from radio to ant doesnt matter. RG8 for longer runs tho. Back in 1972 I installed a homemade halfwave antenna 20' up an oak tree. Ran RG8 10' down and 12 ' over to my awning, another~ 20' to a front window then about 8' in to my base station (Realistic Navaho). Roughly 50 ft total. I was about 2mi as the crow flies NE from the junction of Rte 301 and Rt4, elev ~60'. I could talk with truckers on 301 almost 18 miles both N & S and 4 E & W.. (with a 1/4 on the trunk of my convertible - SWR on19 1.3 - barely 4mi.) Part of a small net, we helped traffic much as possible during bad weather. Gone are those days and they cut the oak tree down in '81 after storm damage. ☹☹ BTW in closing. Now a days where I live (with limited height available) I find that a full 1/4 vertical fiberglas with a short ~4' car roof top ant makes a fair 1/2 wave dipole. PS Id like to hear if someone tries TWO of those short loaded antennas joined as a dipole. 73's to all from a very OM.

Back in my CB days always liked that on a 40 channel rig you can go to ch40, check SWR, one click to Ch1 check SWR again and then add or subtract antenna length until you get the same at both ends and you will be bob on at ch20:) I love your CB SWR curve diagram it explains all of that in one sketch :)

What's funny, I bought some coax a while ago for sdr and wondered why the hell it was sold in 18 ft lengths.... Makes more sense now!

Awesome video!! I do ha e a question though, and no one seems to have an answer. How does adding an amp, between your antenna and radio, effect your coax length, if at all? I want to put my amp in the trunk, my radio under the dash, and the remote to turn the amp on by the radio. Please help!?

Dumb question- where did you get that paper that you're drawing on? I used to be able to get it at a local store here in the states, but that store closed. I can't find it anywhere.