11m / CB Radio: How Long Should My Coax Be?

[@M0RMY]

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

[@petertyrrell6690]

An antenna driven element requires something to work against. A dipole, for example, has a driven side and an rf grounded side that work together to transmit. A 1/4 wave cb vehicle antenna will require two components to work, the bit sticking up, and some sort of rf ground. If the vehicle has a metal body, then it is the rf ground. If the vehicle body work is non metalic, the coax will be the antenna rf ground, and it should then be then an appropriate length.

[@Brenda-jf2pe]

Great video, wish I had the property for a DX commander! I bought the Eurocom hf 360 from UK, will put it up this spring! Chow 73 JohnBoyUtah KJ7TBR 😎🇺🇸📡🎙

[@george-ev1dq]

@@petertyrrell6690 BOLLOCKS

[@petertyrrell6690]

@@george-ev1dq If you, (out of your vehicle) connect, your 1/4 wave CB antenna, with it's factory 17.1" coax, to your radio, depending on it's proximity to its surroundings, its SWR should be close to 1:1. Why? As sold, the 1/4 wave antenna is a center fed coaxial dipole, with half of the coax as 1/4 wave stub. So rf travels along the coax (an electrical 1/4 wave length), meets the very high resistance of the end of the quarter wave stub and travels no further. The coax sheath is part of the antenna. A half wave length of coax repeats the impedance of the antenna connected to it. This would be 50 ohms in this case, and is why the coax length is 17.1 feet. Installing a CB antenna in a metal bodied vehicle, causes the antenna to now be a ground plane antenna, as the body of the vehicle is now the rf ground. This is why you trim the antenna length, to match it to the vehicle's body electrical characteristics. I hope this helps.

[@george-ev1dq]

@@petertyrrell6690 Nope, co-ax length is a myth

[@_PikeWxRadio]

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!

[@DXCommanderHQ]

Ah cool!

[@arconeagain]

I don't understand, did you not have an SWR meter, or one built into the radio? Why not just think for yourself, and if unsure, research anywhere else online instead of now trusting YT?

[@_PikeWxRadio]

@Jeremy Frances I dont understand your inability to comprehend plain English. Do you not know how to read? Was anything I said incoherent? Did you not watch the video? My point was that as a totally new and having no mentor or guidance at the time other than online research, I found minimal trustworthy sources. All CBer's have to worry about is SWR and have they all these crazy theories and schemes for their illegal rigs. I never said I trusted YT, but I trust Callum because he's transparent and actually runs a radio business. Who else should be trusted instead, you? Crawl back under your rock bud. It's much safer for you in there.

[@simonappleby4224]

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.

[@DXCommanderHQ]

Hey Simon.. BRILLIANT story :)

[@TheArtofEngineering]

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

[@stargazer7644]

Keep telling yourself that if it makes you feel better :)

[@indridcold8433]

Thank you! Those jerks with long, thick, black, imposing, cable hanging low in the wind think they are all that. When the truth is, it is the power that drives the fire from your wire!

[@jeffreyleonard7210]

Mine's thicker?

[@warrenpercell297]

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

[@DXCommanderHQ]

i know.. We all fell for it!

[@poormanstube]

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.

[@saxmusicmail]

Just this past weekend I went through all of this, exactly, but all calculations made in feet (468 / freq in mhz) with my grandson. I have the Rig Expert AA-54, which graphs. We built a dipole, deliberately made the wire a few inches longer than calculated. The dip was offset just as you showed. We recalculated from there, cut 1.5" from each side, centered the dip right around Ch. 20. SWR was 1.5 on Ch. 1, 1.2 on Ch. 20, and 1.4 on Ch. 40. But he got to see all this first hand. A great lesson! He could not transmit... he had his Dad's CB, but could not find the microphone.

[@DXCommanderHQ]

Ah!

[@saxmusicmail]

My grandson called me a few days ago. He tore the store room apart looking for the mic, no luck. I ordered him one which should be there any day. I've got him lined up for a ham cram, so maybe he'll get licensed.

[@SHAMAN.VISION]

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

[@jaym1301]

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.

[@DXCommanderHQ]

Awe, thanks friend!

[@richarde735]

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.

[@DXCommanderHQ]

Brilliant!

[@melvance7281]

Um. Not being critical....but..... the biggest clue to your issue is summed up in one word from your post.....Amp The archer SWR meter is fine..even in todays tech, it's fine....not as fancy as other things out there, but still an accurate measure of the match between the radio and antenna...if used correctly

[@nicke.3011]

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.

[@garyclark4930]

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

[@DXCommanderHQ]

That's it!

[@eyeinidas]

I agree, if the antenna is right, the coax can be any length. Coils and common mode chokes can be a good thing, if you have excess.

[@windseeker2357]

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.

[@DXCommanderHQ]

Brilliant!

[@m0zeh]

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

[@paulm0hpd319]

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 👍

[@DXCommanderHQ]

Hmmm. I wonder if I might become out of my depth..!

[@paulm0hpd319]

@@DXCommanderHQ I am sure you won't be out of your depth, I think it's a totally misunderstood subject that needs someone with a platform you have to help dispel the myths ,although you've mentioned most of where the myths have developed from every length with a feedpoint mismatch will show the radio a different impedance ,think more on this point may help with the understanding of the subject, also common mode current can cause issues with different lengths

[@battlestarone]

@@DXCommanderHQ lets have coax shoot out,,and but the myth and theorys to the test.,,,would be intresting results.

[@DominicMazoch]

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

[@Mark19960]

I also want to add mate that they use the coax quite often to tune the system. Some of the amplifiers they make have such bad tuning they use the coax to trick the radio into a proper load. I’m sure they will be along to argue with you mate. Cheers.

[@DXCommanderHQ]

I'm sure too. It's still wrong!

[@paulm0hpd319]

​@@DXCommanderHQ it's not wrong Callum it's just another way to provide a conjugate match to the transmitter to produce its maximum power into the system, reflections by Walt Maxwell covers this subject at great length

[@DXCommanderHQ]

It's "wrong". Absolutely wrong.. You can make a tower out of soft spaghetti - that's wrong too.

[@paulm0hpd319]

@@DXCommanderHQ using feedline as an impedance transformer is not wrong what's wrong is not understanding that feedlines become impedance transformers with a mismatch

[@rolandweaver7983]

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…

[@DXCommanderHQ]

Hey Roland.. I find it difficult to speak "English" sometimes!

[@arconeagain]

As an RF expert, what are your thoughts on CMC in regard to this one? After all, 18 feet is close to three quarters of a wavelength of 0.66 coaxial on at least one channel of the 27Mhz citizen's band.

[@arconeagain]

You have not answered my question. You said that anyone that believes in this IDs them as not having any fundamental idea about RF theory, and you claim to be an RF expert. Did you forget your transmission line theory? Probably best you delete your post to save any further embarrassment.

[@DXCommanderHQ]

@@arconeagain I'm not an expert. I don't trust anyone who says so. I'm a practical scientist. Call a professor at the local university if you want to speak to ao.eone about theory. Beware that I'm not alerted to comment threads so you won't probably receive another reply unless I'm lucky and happen to spot it.

[@arconeagain]

@@DXCommanderHQ my comment was directed at your mate Roland, aka self proclaimed RF expert. It's truly amazing what you see, hear and read here. I mean, imagine a radio enthusiast saying they don't care about CMC. It was obviously a desperate bid in covering up a video blunder, your apostles might have followed the breadcrumb trail if they had a brain between the lot of them. Wait til I tell my mate about this one. He's a ham since god knows when, who takes great joy in watching fellow hams... well, just be hams. Remember this, it's called 'amateur' radio, for a reason.

[@jerrym1183]

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.

[@paulm0hpd319]

EXACTLY!!!! think this has been overlooked here

[@jerrym1183]

@@paulm0hpd319 Hello Paul - catching up all the comments here, your call seems familiar, have I worked you on 80 meters before maybe you were mobile?? Jerry KC2UT here

[@paulm0hpd319]

@@jerrym1183 possibly ,mainly mobile upto recently

[@alunroberts1439]

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.

[@DXCommanderHQ]

Speaking to a goldfish! LOL

[@timprice1284]

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

[@1vester1]

got to love the old 102in whip cb 1/4 wave... looks crazy but it works... like 80 bucks to set one up now. i have done moved on to vhf/uhf kd5rch

[@edwardambrose8704]

In the mid ‘70’ s rule of thumb was 11 feet 10 inches of 8u cable for 23 channels ! Had 40 ft. SWR was 1.1 across the spectrum ! 5/8 wave radio shack antenna and got out like a champ !

[@eyeinidas]

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

[@robrs2000]

What do you consider a poor ground? some of my best results, mobile, have been with a mag mount as near to the middle of the car, so the outer shield has no connection to ground? I think a lot of confusion with anything antenna related is that as people who have a good knowledge of electronics we forget that radio is electro-magnetic :) (I may have misunderstood but I agree if you are driving a fibreglass car, that would provide a poor ground for radio)

[@eyeinidas]

@@robrs2000 A magnetic mount is nice. I use one on my pickup. It came with a long cable attached. But, I think it's designed to use the vehicle as a ground plane. As I understand it, the RF doesn't see the base as an open, but passes through easily to the ground side of the coax. That works well on a steel roof top. When you buy an antenna at the truck stop, it's usually made to mount on the mirror and it's packaged for the rocket scientists that relocate the freight across the interstate system. The bodies of the modern tractors that they pilot are made of plastic, fiberglass and aluminum. They hang an antenna on the mirror mount and it needs a counterpoise. I've actually added a counterpoise on my rig, but it didn't change much because I had already run a ground wire from the mount all the way to the chassis. I have a 1:1.6 SWR with no tuner. I use a tuner, though because I slip into spare trucks, sometimes that haven't had as much thought put into their antennas. And my coax is much shorter than the eighteen feet recommended by antenna manufactures.

[@robrs2000]

@@eyeinidas Yes, I thought at the end of my reply that you may be talking plastic cab type situation. I have always wondered, with a big trailer if there is any millage in a wire antenna down the length of the trailer, probably not very convenient if you are always swapping trailers :)

[@eyeinidas]

@@robrs2000 It would be fun to try. I also pull these old steel tanker trailers. I want to mount an antenna on that thing and see what kind of range I get. It would require a longer cable to reach. I don't think I would loose to much on HF running a little long all the way back to the trailer midpoint.

[@diamondmetalworks13]

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.

[@DXCommanderHQ]

Great idea!

[@VE3NMW]

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

[@DXCommanderHQ]

Great to hear!

[@g4lmn-ron401]

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.

[@DXCommanderHQ]

>> "radio is radio, it's all good fun" - well said Ron :)

[@tobyticehurst]

Ditto, we have to break the stigma. We are all on the same boat just with different sized paddles.

[@ac3146]

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 😂

[@DXCommanderHQ]

Arcing? Well, unless you are running seriously high power, I wouldn't worry about that. I mean kilowatts - and the first thing to go would be the connectors, flash over of insulation etc.. BUT unless you actually measured the velocity factor, you would probably be wasting your time.

[@cliffyoung5712]

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.

[@DXCommanderHQ]

Well, you know even my 12.4 installation with 1,000 feet of 32 radials only measured 45 ohms.. I can't get it any lower...!

[@ChiefMade]

Fantastic as always Callum! 73

[@petertyrrell6690]

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.

[@steve87uk]

How long? Long enough to reach the antenna 🤣

[@pc4ad]

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!

[@DXCommanderHQ]

Yeah Anton, I was schooled in SWR the moment I bought my radio! Like it was SO BLOOMIN IMPORTANT!!

[@arconeagain]

The text from that company did not simply state SWR, it stated SWR readings. See if you can figure it out.

[@Aswaguespack]

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

[@j.p.thearmoredchef]

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.

[@DXCommanderHQ]

You tried! Imagine the problem though.. A DX Commander with multiple elements from say 80m through to 10m.. Now .. Guess how long the coax should be! LOL Actually, Tom (M0RMY) sent me his SWR curves.. It's on our website under FAQ.. That'll stump him!

[@winterburan]

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🙂

[@DXCommanderHQ]

Haha!

[@arconeagain]

I'm not sure what you're saying on how they calculated the length, but why not a half wavelength or more? This way you can actually see the impedance of the antenna when you plug in your analyser. As for 213 minimum, that's just ridiculous. In a mobile setting? Quality RG58 is fine, and far more practical. The difference in losses is negligible, and couldn't possibly be detected on a receiving meter. That's about the stupidest thing I've read on YT in quite some time. Where do you people get off?

[@winterburan]

@@arconeagain There was talk of fixed and non-mobile installations, try to stay on topic and not daydream, in the channel I have never seen road tractors, trucks, boats or cars, and usually for a 5/8 antenna between descent from the mast and section to get to the CB there they are more than 20 meters, yes the RG58 is fine in a car or truck, I brought back a theory from the 90s, dear wise man !

[@arconeagain]

@@winterburan well maybe be less vague with your comments. I still don't understand what you're saying about the length calculation. What's wrong with the 198 if they're using a usual mil spec RG213 or 58?

[@richb.4374]

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.

[@eyeinidas]

That's often the case with mobile radios installed in cars and trucks because the don't have a good rf ground or radials for a counterpoise. Cars and trucks are made out of plastic and fiberglass, these days. Lol

[@stargazer7644]

The length of the line doesn't matter if you have a good match. It DOES matter if you have a poor match, because there are standing waves on the line. Where you measure makes a difference when you have a poor match because of what the VSWR meter actually measures - voltage. This is why some people believe changing the coax length fixes bad SWR when all it does is fool your meter.

[@adammcleod5026]

@@stargazer7644 exactly this. Well matched no problem. Bad match will give different SWR at different points along the coax depending on the wavelength.

[@paulm0hpd319]

​@@stargazer7644 it's not fooling your meter it's measuring the impedance at that point

[@arconeagain]

@@paulm0hpd319 exactly. Otherwise, how do they expect matching stubs to work?

[@seeharvester]

I think I'll continue to cut my coax to multiples of 1/2 wavelength. Which for LMR 400 @ 27.4 Mhz with a velocity factor of 85% = approx. 15.2575 feet or 183.09 inches per 1/2 wave. That way I can check the swr @ 27.400 from the shack to make sure everything is ok. And with only 1.2 db of loss @ 100Mhz @ 100 feet, I'll be getting the most I can out of my 4 watt CB.

[@bill-2018]

Why not try random lengths of coax and see for yourself if there is any difference? G4GHB.

[@geoffpriestley7310]

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

[@alangoulding4252]

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

[@DXCommanderHQ]

Ah thanks Alan!

[@etzow]

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! 😊

[@stargazer7644]

As a newly licensed ham I once installed a 150 foot run of RG8 going up the tower to my 440 MHz beam. I checked the SWR after install and found it was a good 1.2:1 all the way across the band. Then I noticed I had forgotten to connect the other end to the antenna and it was just hanging open at the top of the tower.

[@DXCommanderHQ]

HAHA!

[@DXCommanderHQ]

@star gazer - that's SO FUNNY!

[@1OFGODSOWN]

@@stargazer7644 Ham Radio is your Career? That’s really strange?😵‍💫🎙

[@stargazer7644]

@@1OFGODSOWN lol yeah I guess so. Words are hard.

[@lyfandeth]

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?".

[@GroundControl204]

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

[@DXCommanderHQ]

Waves back!

[@SebastianPachla73]

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.

[@DXCommanderHQ]

Yes, OK ! :)

[@a2phil]

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

[@DXCommanderHQ]

Friendly hams.. I don't find that. Most people seem happy to help from what I hear.

[@Montaguy]

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

[@DXCommanderHQ]

Yes Sir.

[@preparinginnh1203]

Back in the day I drove a truck when CB was big. When I wanted something done I’d go to a tech and ask them about coax length. If they started talking about the myth I’d leave. Seemed like a good way to find somebody that I could trust to fiddle my gear. 😁

[@DXCommanderHQ]

Good tip!

[@G0USL]

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

[@DXCommanderHQ]

HAHA

[@arconeagain]

In this particular instance/example, that is, using 18ft of 66% velocity factor of coaxial feedline for a typical mobile installation, you'll find that you 'do' take the velocity factor into consideration.

[@simply-ericcole8201]

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 ;-)

[@TedHallII]

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.

[@DXCommanderHQ]

Please don't tell me you actually cut the coax specifically for the match? 50 ohms is 50 ohms :)

[@williambarrett70]

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!

[@DXCommanderHQ]

Amazing.

[@alanslade2319]

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 💯👍

[@DXCommanderHQ]

YES SIR! Finally :)

[@johnhess351]

Truckers are smart, but they do not really understand radios and antennas very well. The CB companies and other industries industry has long taken advantage of their relative ignorance of scientific things to sell them snake oil of various sorts from radar jammers to anti glare interior cab lights to fuel line magnets. Are two antennas better than one...etc

[@leighstevens]

Thank you for explaining it in simple terms

[@DXCommanderHQ]

Glad it was helpful!

[@mrkultra1655]

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.

[@arconeagain]

You now 'know' from one guy's opinion on YT? The same guy that basically opened with, 'I'm not an expert on transmission line theory'? C'mon mate, surely you have the ability to think and reason for yourself.

[@bill-2018]

It is nonsense. The RSGB Handbook nowhere mentions cutting coax to specific lengths for a particular aerial, either in the modern one or one I have from 1974 with a couple in between. They baffle people with figures. It sounds good. I remember in a pub way back someone saying, "You're only a radio amateur but he's a CB'er". I was speechless. Overnight CB'ers became experts in radio where it took me some studying to get my licence. Perhaps I should have taken up CB, I'd obviously know more overnight! 73, G4GHB.

[@petertyrrell6690]

​@@bill-2018The driven element of an antenna requires an rf ground to work against. With most antenna the rf ground is built into it, like a center fed dipole for example. Where the rf ground component is build into the antenna, coax length is irrelevant. With a mobile antenna, the rf ground is the vehicle body, unless it's none metalic, and then the coax shield will become the rf ground, including whatever else is available. va3hr va3pet

[@bill-2018]

@@petertyrrell6690 I've used a gamma match and delta match for driven elements. Yes a badly bonded coax to the vehicle can cause problems and the coax acts as a counterpoise earth. 73, G4GHB.

[@Centar1964]

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.

[@DXCommanderHQ]

It will because the coax is part of the antenna.. When it's NOT part of the antenna (most 50 ohm systems), length doesn't matter.. Just loss.

[@bill-2018]

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.

[@DXCommanderHQ]

Good point.

[@itisnotmee]

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

[@Popgunner101]

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.

[@DXCommanderHQ]

All good points!

[@bill-2018]

CB'ers do seem obsessed with getting as low as possible SWR. I wrote these figures down a while back. SWR % POWER OUT 1.0 100 1.1 99.8 1.2 99.2 1.3 98.3 1.5 96 2.0 88.9 3.0 Not Good 75 I aim for under 2, 1.5 better. 1.5 and below is great. All QRP here, 5 Watts or less so still 4.8 Watts at 1.5. G4GHB.

[@jozyphilyaw9339]

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 😄

[@DXCommanderHQ]

HAHA. You proved them wrong! :)

[@MopH3ad]

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

[@arconeagain]

This so you can look at your antenna impedance from the shack.

[@ChrisDitchDigger]

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

[@DXCommanderHQ]

Much appreciated!

[@ghz24]

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

[@DXCommanderHQ]

Good point!

[@YouTube_User-9]

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!

[@nashvilleoutlaw]

I always did the opposite for swr and antenna length. If it's lower on 1 than on 40 the antenna wants to be shorter. If lower on 40 than on 1 the antenna wants to be longer. The swr is pointing the direction the antenna needs to be adjusted.

[@ScatManAust]

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.

[@DXCommanderHQ]

Yeah.. Actually I would say that in the MAJORITY of cases (certainly in the last 5-10 years) the snobbery of ham radio ops agains CB is now in reverse. It seems to be *SOME* CB ops who think the ham radio community are from some different planet and we all grow vegetables or discuss the latest doctors appointments. Most - correction - ALL of my mates on ham radio don't have an issue with 27MHz. Includes me..

[@arconeagain]

There is so much more to transmission line theory than SWR. So what makes you think this is about SWR?

[@simon_mera]

Bob Ross of CB! Learned a lot, thank you!

[@tomaskey6844]

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.

[@jerrym1183]

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

[@stargazer7644]

They're at 50 ohms every time you have a perfect 1:1 match. That is to say, once in a while.

[@DXCommanderHQ]

I have never seen a vertical under 45 Ohms (even with 1,000 feet of 32 x radials. And I have never seen a tuned dipole out of spec by more than around 80 ohms. Therefore, I'm a 1.5:1 man myself.

[@jerrym1183]

Re the 100ft per leg Vee Beam here, I have now added an "ugly choke" at the feed point, 10 turns Rg6 on a 7 inch form, and then to a 1:6 Type 31 transformer to the 2 vee wires, and is working noticeable better! I Tx here at semi QRP 50 watts. My 25 MHz WWV reception here went from S9 +10 to S9+20 with most recent feed-point mods.... Am being heard quite well I believe... Is nice to TX 14-30 MHz in style once again....

[@NukaVaultReadiness]

Half of the fun is experimenting. Thanks Callum!

[@DXCommanderHQ]

Yeah.. great!

[@jasonbabila6006]

I’ve installed different lengths of coax mainly RG8X RG400, RG142 or RG58A/U between the antennas and radios from 12’ to 50’ and it depends on how far the antenna is from the radio and never had any issues but as long as the antenna is tuned.

[@DXCommanderHQ]

You got it.

[@acestudioscouk-Ace-G0ACE]

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.

[@timg5tm941]

Ha yes it’s the good old “I swapped RG58 for RG8 and my station has been transformed” myth!

[@DXCommanderHQ]

Groans! LOL

[@KE6DOA]

@@DXCommanderHQ hahahaaa 😂

[@melvance7281]

Um. After more than 40 years experience with CB radio, ive got a couple observations..not attacks....not trying to trigger anyone IF your antenna is resonate,properly grounded, properly installed, coax length shouldn't matter If you need a specific length of coax to match, you got a problem with the antenna or installation

[@DXCommanderHQ]

You middle line was perfect.

[@lomgshorts3]

Reflected power is always additive and is not wasted as heat. The trick is to get reflected power 180° out of phase or as close as you can get to 180° out of phase. With the copper losses, and with the velocity factor of the feedline, you have to get the length just right before you can get the phase just right to have additive power on each reflection. It is possible, but you can only get really lucky before all power is additive. All feedlines of any kind are different from any manufacturer in copper losses, velocity factor, and reflective structures the feedline passes close to. In what was said in the video here, you just have to trust to luck !!

[@DXCommanderHQ]

Or give up and install a flux capacitor.

[@theredbaron057]

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.

[@tedmead465]

Callum i think the biggest problem cb experts have is they are taught and use commercially manufactured antennas. Antenna performance depends on a lot more than manufacturers statistics. Like you I build my own antennas. Matched to their feedline i rarely have over a 1: 1 swr As an example my 20 meter homebrew dipole at 32 feet above the ground. Gets me some great coverage as i live in a valley. My furthest calls to date is half way around the world on 5 watts ssb( from pennsylvania usa to France, Scotland, and Russia) There is a lot more to antennas than just swr! I dont fault the cb experts because they may not have had the proper education. I highly recommend they get the arrl antenna guides and handbooks. Love all you videos!! 73 Ted Kc3tec

[@DXCommanderHQ]

Good point.

[@rnrbishop]

Wonder what they’d do with a doublet?

[@Zif-the-Old-Herring]

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.

[@DXCommanderHQ]

Yes, it's quite simple really..

[@peterwaine923]

Stick a dummy load on any length of coax you will get a 1 to 1, so any length does not matter, its the tuning to 50ohm's of the antenna on the coax line.

[@jamescstanley5018]

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

[@DXCommanderHQ]

Right on!

[@MrSIZEMIK]

It's very simple, coax length depends on two conditions, 1) if the antenna has a load match inductor at the base, the 2 PL259 contacts produce a closed circuit 2) no inductor, the 2 PL259 contacts produce an open circuit, , , So condition 2 has to have a coax that has a critical length !!

[@DXCommanderHQ]

And that would improve your signal... Yeah OK.

[@MrSIZEMIK]

@@DXCommanderHQ The way you describe it, by magic, the transmitter corrects the phase along the coax to antenna, , , Yeah OK !!

[@MrSIZEMIK]

@@DXCommanderHQ Hmmmm, , the velocity factor does not effect length or frequency, 300 / 27.555 = 10.887mtr / .66 = 16.495mtr : 300 / 16.495mtr = 18.197mhz, , , so is it 27.555 or 18.197, of cource it is still bloody 27.555 ha ha, i have found it is allways good to have an objective opinion, i find i learn more !!, , , i do like your video's tho, they get me thinking, , ,

[@arconeagain]

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.

[@aquariumsmaintainedbyandy8408]

Fantastic information and fantastic video

[@TRUCKERWILLY98]

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

[@jamesmoore6424]

I came from CB, a friend of my dad's got me interested and he was a CB operator before getting his ticket.

[@DXCommanderHQ]

Nice!

[@davidblake6889]

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.

[@DXCommanderHQ]

Yeah nice! (although I've never cared about common modes myself..)

[@arconeagain]

You have the answer! For example, a quarter wave antenna has a low common mode input impedance. By employing 3/4 wavelength of coax, you transform this impedance. And as my earlier post read, coax with a velocity factor of 0.66 at 27.055 (truckie ch) will be almost exactly 18ft long (1.38mm short). So it is not a myth at all! One very good reason to minimise CMC in the car is for noise suppression.

[@bill-2018]

Use any length of coax and put a ferrite ring on to stop CMC. I've been doing it for years. G4GHB.

[@321CatboxWA]

You know you could still be a cb operator and apply what you learned. It's not too late . CB radio still has a place for you! Dxing is legal to do now and the skip is rolling. 73s

[@kiweekeith]

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

[@DXCommanderHQ]

Glad you enjoyed it - I don't recognise your handle in the comments. Maybe you are new to me.. Welcome!!

[@kiweekeith]

@@DXCommanderHQ Thanks for the Reply Callum .... OK .... "WR" .... = World Radio 'Group', ..... and "KK" ... = Kiwi and Kangaroo 'South Pacific' .... A more 'Local' CB Radio Group... Thanks for the 'Attic Antenna' vidclip .... Also a Very informative and entertaining vidclip ..... Best to You and Yours from Christchurch, New Zealand

[@daveengstrom9250]

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

[@DXCommanderHQ]

Me too.. I did do a cover of Comfortable Numb once.. kzbin.info/www/bejne/a4e2YqGtnaafoa8

[@williambarrett70]

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

[@DXCommanderHQ]

Yeah, I had a PDL2 - great antenna!

[@frederickwise5238]

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.

[@somethingcool7903]

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

[@robrs2000]

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 :)

[@DXCommanderHQ]

Me too!

[@tobyticehurst]

Am I right in saying, if an antenna is tuned to 30ohms it will perform better on TX and 75ohms will optimise RX. Therefore the reason we settled at 50ohms for transceivers is to have the best of both worlds/happy medium? Could be an interesting subject if there's some truth behind this speculation.

[@VE9ASN]

No, also a crazy myth

[@DXCommanderHQ]

So I never knew that myth existed. Gawd, what other rubbish are people going to suggest! Haha. For interest.. in *ALL* my experiments, I have never managed to get a vertical below about 45 ohms, even with 32 radials and over 1000 feet of wire. Theoretically, it should have been 35 ohms.. And for dipoles, they rise and fall between 40 ohms and 100 ohms depending on height - then eventually settle at 73 ohms - which is next to nothing difference to 50 ohms in terms of efficiency. I THINK I have a video that mentions that coming out (I can't remember, I have a few "in stock"..

[@tobyticehurst]

@@DXCommanderHQ Well now you have Cal (your welcome?) I can not remember where I heard it, probably in the depths of KZbin binge somewhere LOL. Yes, a friend and I noticed the effects of height on a dipole when building an invert-v, 2m difference in height made a surprising change where it resonates (ideal for 80m without using a tuner, adjust height instead). Thank you for putting the above myth to bed and ill look forward to seeing your take on diploe height effects.

[@tobyticehurst]

@@VE9ASN Thanks Les, I'm sure there are a few more in the bank that will raise their ugly head. Everyday is a school day. M3TJT

[@adammcleod5026]

@@DXCommanderHQ this one is actually true from what I understand. And as you said it is a system, as long as it is balanced it could be 450 bananas. "Lowest loss: This depends on losses in the internal dielectric in a coaxial cable. For the air-filled coaxial, this occurs at approximately 77 Ohms, or at approximately 50 Ohms for certain dielectric-filled cables (more on this below). Highest voltage: This is based on the electric field between the center conductor and sidewalls in the air-filled coax cable. The electric field in the TE10 mode is maximized when the conductor is constructed such that its impedance is approximately 60 Ohms. Highest power transfer: Coaxial cables of any size might be long enough to act like transmission lines and support wave propagation. The power carried by a coaxial cable is limited by the breakdown field and the impedance of the cable: V2/Z. It turns out that, for the air-filled coax operating below the TE11 cutoff, power transfer is maximized at about 30 Ohms."

[@m7trsradio]

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

[@DXCommanderHQ]

Very true!

[@demonkey123]

Thanks for the explanation. Can you explain a bit further why lengthening and shortening my antenna when I’m tuning has a dramatic effect on my SWR but the length of the coax doesn’t matter please?

[@DXCommanderHQ]

Because the antenna is like the string in a piano however the coax are just the keys you hit it with. Coax length doesn't matter. Bloody good question!

[@get__some]

got a new radio peaked and tuned at a cb shop. that was a mistake. he told me i had to have 18ft of coax. went into a long story about how it always does better. twice as good as 9ft... he said, well let's go check your coax and antenna with my analyzer. kept my mouth shut. we got out to the truck, i exposed the end of the coax, he plugged in analyzer, it showed 1.18swr. i said that's only 10ft of lmr400, so how could the swr and my performance be any good. that was the end of our conversation. 10ft was because that's how far it needed to be. 9 was too short, 11 was too long. didn't even know what i was doing, but he proved to me the 18ft thing was balderdash. thanks for the video !

[@DXCommanderHQ]

Wow!!

[@get__some]

@DXCommanderHQ thanks for letting us share experiences in your comments section. lots of learning happens here and makes future experiences less surprising.

[@M0RMY]

I am returning to this topic as it is still ongoing as a myth on various forums. Riddle me this one: "If you need a specific length of coax for a good match/swr, then how come my Tarheel II screwdriver antenna matches perfectly from 80m to 10m using a single random length of coax in my car?" Hmmmmm 😀

[@DXCommanderHQ]

Good point Tom!!!

[@OldAgeTeddyboy]

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...

[@DXCommanderHQ]

Hey hello. Yes, I think you also dropped me an email.. I have no idea what people don't want to use the RIT knob. I do all the time. Some gear is off by a whisker. We should just use it..

[@turboclub7658]

God you will destroy the sanity of 80% of CB Radio operators in the US with your comprehensive explanation! 🙂 About time someone actually did who knows what they are on about!! VSWR? I avoid all FB discussions on both these subjects.... Heliax on CB solved any extra cable concerns HF & UHF ;-)

[@DXCommanderHQ]

HAHA

[@jamesrush5367]

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!

[@DXCommanderHQ]

Ah!!

[@billybiker1383]

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

[@DXCommanderHQ]

Billy! Thanks so much :)

[@G6EJD]

Coaxial impedance is derived from Z = sqrt(L/C) where L is the inductance and C is the Capacitance where both values are per-metre of cable. Your VSWR graph can also have Ohms on the y-axis so for a 50R system 2:1 would be 100R and 3:1 would be 150R derived from VSWR=Zload/Zsource, it's a good way of estimating antenna impedance from the graph. Yes there is a bend radius for coaxial cable, but I agree with you Cal, what's reported and the folk lore is all tosh... We need more videos like this to help dispel what is a lot of nonsense circulating around. Well done.