More coax tuning 1/2 and 1/4 wave 11M observations

[@electromechanicalstuff2602]

Conclusion my dummy load was defective. So yes this is correct to do it this way. But a good dummy should be X=0 SWR=1. After checking with new dummy it's all zeros

[@RC-Heli835]

Dave in the USA says to put aside all 3 ft jumpers and use 6ft, 9ft or 12ft thru all your equipment. Then from the starting point at the shack including all jumpers combined run coax to the antenna in multip'es of 11 ft so that all of it stops on 55, 66 or 77 including your jumpers. He says it only works for 11 meter. Dave has the last article on this page. www.radiomods.co.nz/coaxlength.html Also for car he says don't use less than 20 ft. He says you may not need twenty feet but roll it up and hide it somewhere close to the antenna as possible. Supposedly the longer lengths help to keep RF noise down. My 3 ft jumper has worked fine for my base setup until someone gave me a one pill 60 watt amp. I'm not blaming it on the 3 ft jumper that I have but the SWR is unusable from the amp to the antenna with the amp on. Its fine with the amp off. An extremely knowledge able Ham guy Dave Cassler on youtube says that cutting in half wave lengths is only good if your trying to get one frequency as good as you can possibly get it Like if you broadcasted a show on channel 33 and wanted it to be as good as possible you might cut carefully calculated half wave lengths. Performance will be less the farther away you go from the frequency in which the half wave is cut for. kzbin.info/www/bejne/paSZYY2Vftl6qLc

[@rallypoint1]

@@RC-Heli835 I read that article too. My mobile has 33’ total feet of coax. 6’ from antenna to choke(3’) 15’ to amp, 6’ to CMF choke(3’) and then mounted direct to radio for total of 33’. Works great!!! SWR is 1.18 give or take across 11m. Could be coincidence. I don’t know. It just works for me!!

[@RC-Heli835]

@@rallypoint1 Awesome! What kind of amp are you running?

[@rallypoint1]

@@RC-Heli835 a little kl203...great bang for buck!!

[@johnyoung1128]

Tuning the feed line for a 50 Ohm load does not make the cable “disappear” the loss will increase with length regardless, indeed losses will be greater in the coax if trimming its length is used to correct for a miss tuned antenna.The condition you set up was an open circuit in parallel with 50 Ohms because transmission line theory says that a half wave transmission line will show the same impedance it’s terminated in every half wavelength. This will repeat every further half wavelength. The quarter wave situation is different because it will show an inversion of impedance every 1/4 wave, that is a 1/4 wave terminated in an open circuit will look like a short circuit every odd 1/4 wave. That theoretical situation is altered somewhat by line losses in real world situations. If you could measure the impedance along the feeder when terminated in it’s own characteristic impedance (ie 50 Ohms in this practical case) it would be 50 Ohms at all lengths, this is referred to as a “flat” line. This also means that if the antenna shows 50 Ohms at its feed point then the impedance presented at the other end of the coax ie at the radio end will also be 50 ohms regardless of its length! Indeed you can get a perfect SWR with a long enough piece of lossy coax with no antenna connected at all! This all means that in a vehicle installation with a single properly tuned antenna feed line length can be regarded as irrelevant. The 3 foot increments or 6 foot increments theory is invalid because it will progress you through alternating 1/4 and 1/2 wave conditions which will have differing effects on results, and don’t get me started on velocity factors. By the way RG 213 has a VF of 0.66 and RG 400 has a VF of 0.695 so the tuned length will be different for each of them. The 20 ft length will provide less noise proposition is rubbish as lengthened cables will give a lower signal to noise not greater. Tuned lengths do have their place in complex installations but for average installations it should be regarded as snake oil.

[@melvance7281]

Look. I've been involved in CB radio since the '70's and a ham since the mid '80's. For a single antenna, IF your antenna is very close to 50 ohms, the coax length shouldn't make enough difference to matter....until you get up to several wavelengths....by that point, you need to conserve every micro-watt of power to overcome the loss in the coax Multi antenna installations are another story as the length of the coax provides the correct impedance match

[@electromechanicalstuff2602]

K. How much power u run?

[@M0RMY]

@@electromechanicalstuff2602 Makes absolutely no difference

[@nashvilleoutlaw]

When making jumpers I just trim until X reaches 0 ( Z on my mini60) if you really want to get picky, I can scroll up and down to find the frequencies where it goes back up to 1. Then add the high and low frequencies together and devide it by 2 to get the true center. If you think about it for an antenna. If you set your antenna to the perfect length for the band. Then hook an untuned piece of coax to it. You have to lengthen or shorten most antennas to compensate for the mismatch. Seems like that would affect the antennas performance, radiation field pattern and takeoff angles.

[@808pathfinder]

Radio operators should all have a analyzer and when you have one, it all starts to clic and make more sense, thanks for making this video, I hit the like n will share it to all my friends

[@Aimsport-video]

Tune the antenna at the feedpoint. That will minimize reflections making feed line length irrelevant.

[@electromechanicalstuff2602]

U can tune your antenna till your blue in the face. Just like in the video it's a perfect antenna and yet the only thing that changed was the coax length giving you higher SWR by adding different capacitance and inductance. Even with a perfect antenna your SWR will be worse if u don't have a band specific tuned coax

[@Aimsport-video]

@@electromechanicalstuff2602 Without reflection due to mismatch at feedpoint there will be no standing wave. By coax tuning one is just coping with the frequency of the standing wave interacting with signal, and the commensurate losses and constructive and destructive interference. If changing length or even moving coax vastly changes VSWR, it indicates reflection at feed point as suspect #1 and that bandit is often accompanied by RF on the outside of the coax. Good luck.

[@rockerforlife194]

I cut all my coax in half wave increments and have the best results I've ever achieved. Everything checks out better. Been around radios since a kid in the 1960's and this is the best way to cut coax. Period.

[@paulm0hpd319]

What if you have a resonant folded dipole, what benefit is having half wave length of coax

[@OLDMANGAMING1970]

@@paulm0hpd319 Nothing,,,, The Dipole don"t care if its 50 or 100 foot coax.

[@paulm0hpd319]

@@OLDMANGAMING1970 of course it does, a folded dipole is around 300ohms that's a 6.1 swr ,all the half wave increment is going to do is repeat that 6.1 swr at the radio ,so no benefit of half wave lengths, that said other lengths may bring that impedance down to a more exceptable level

[@paulgrodkowski5839]

Ja zrobie 50 ohm obciążenie ale bedzie cos smiesnego w mojim wieku !!!😶🤥🤥👍

[@bill-2018]

@@paulm0hpd319 Very many years ago I built a 5 el Yagi for 2m. The D.E. was tapped and required 300 Ω to 75 Ω as I was using at the time. I remember it being a ½λ coax cable balun. G4GHB.

[@marcstrauven4697]

Cable Nulling. Any load connected to a coax that is not perfectly matched to the coaxial cable'scharacteristic impedance will have its impedance modified by the coax. Cable nulling allowsyou to remove the effect of the coaxial cable so that the impedance you read shows the impedance of the load at the end of the cable, without the cable modifying effects. Cable nulling is available in the VIA mode, the SWR mode has no cable null feature.

[@electromechanicalstuff2602]

Coax can change the impedance of the circuit tho that then essentially causes a change in the SWR. For instance u take a perfect node coax and a perfect load and perfect output tune on the amp. U can cut the coax anywhere and install the SWR meter and it won't affect the SWR but let's say instead of cutting your perfect coax or attaching it either end you choose to add another 3' jumper from your meter to your amp. Now u have changed the impedance match u had thus changing your swr because your have added some amount to impedance to your amplifier output tune. Now if u have a tube amp u can correct for this with the tune cap but if u have a transistor based amp that does not have a variable tuning cap the SWR will change. U can now either open your amp and change the capacitor to adjust for your output tune or get an antenna tuner that essentially does the same thing. Now if u don't want to do all that. Just make sure all your jumpers are nulls or put your meter in at a half node point both in and out.

[@marcstrauven4697]

Dear Sir, I always zero my coax because while measuring the swr so impedance of my antenna I only want to measure the value of my antenna and not see false values caused by the capacity and induction that the coax causes during the measurement. I once saw and learned this from a radio amateur who was also a civil electronics engineer. Everyone laughed at me when I did this, but none of them got their swr value of their antenna really right, unless they arranged their antenna with the Rigexpert and or the MFJ directly connected to the antenna. There is even a measuring device in which it is explained in the manual that the coax must be tuned for the frequency at which one wants to work. I had attached the link but apparently you-tube removed it. Best regards. 73 Marc

[@MrJaz8088]

If everything is Grounded properly, Antenna, Coax & Station then a Tuned Coax is no different from a Radom length coax A Tuned length of Coax does work, or adding a small piece to tune

[@g0fvt]

If you repeat your test with the t-piece and the quarterwave patchlead you will find you can short circuit the far end and behave similarly to the open circuit half wave cable.

[@electromechanicalstuff2602]

I'll give it a try

[@terryshrives8322]

Really awesome I just learned something new.

[@seeharvester]

but was it correct? kzbin.info/www/bejne/Y4WyqpiXhMuUrck

[@jeffhicks2070]

I trim the coax without dummy load,its hooked directly to mfj and trim other end

[@electromechanicalstuff2602]

What length 1/4 or half wavelength

[@kennethschultz6465]

You can do unewen wawelenghts In cabel using velosety factor But COAX IS MOSTLY USED FOR UNBALANCED ANTENNAS NOT BALANCED WITH LADDER LINE

[@electromechanicalstuff2602]

All I know is I used an antenna analyzer with a standard 12' piece of coax and I could see the lowest swr frequency. I then tuned my antenna to my desired frequency. Swr achieved was 1.45 swr at its lowest point. I then tuned this coax separately to achieve a" invisible" piece of coax. Now my swr is 1.1 at its lowest point. The coax was absolutely playing a role in my overall swr.

[@ericdee6802]

Iam lost as to why your testing coax with a "T" and a 50ohm dummy load??? Coax is unballanced.

[@bill-2018]

Putting the dummy load on the end of coax proves coax is doing what coax should do, it sees 50 Ω on the end of 50 Ω cable and matching it nicely. What you did at first was showing the difference between a quarter wave and half wave open end coax. Coaxial stubs at the transmitter were used to filter out harmonics when t.v. used frequencies around 45 MHz. If you're cutting coax to get a better match at your aerial I would suggest there's something wrong, the aerial is not 50 Ω, it's acting as a counterpoise earth and likely there's r.f. on the outer of your coax. I've never had to cut coax for a good match on aerials. Not one radio book of mine says about cutting coax to one half wavelength for a better match G4GHB

[@electromechanicalstuff2602]

Ham instructor agrees with me

[@bill-2018]

@@electromechanicalstuff2602 Why is it not in any technical radio books?

[@electromechanicalstuff2602]

@@bill-2018 you've used an antenna tuner before right? It adds induction and capacitance to adjust the reactance of the amp to match the antenna. If coax isn't cut on a node of the frequency your using it adds reactance which changes your amplifiers tune. You can use an antenna tuner to make the match but it's going to change the resistance your amplifier sees. Too little and your going to damage your amplifier too much and you loose power.

[@electromechanicalstuff2602]

Are you sure it's not in any books. Like ones that talk about coax velocity factors? And like the instructor said the longer the coax the less it matters. But when you look at it on an antenna analyzer like the mfj I had in this video or a rig expert I have now you can see the resonant nodes in the frequency with every random length of coax. As you change the length that resonant frequency changes. Sometime real world findings are better

[@electromechanicalstuff2602]

kzbin.info/www/bejne/kGPPqalse52ZrKM Here's the video I thought I attached last time. Of the ham instructor showing it. Coax starts at 31 minutes

[@jluke6861]

Thank you

[@franciscolopez3229]

I tried making a quarter wave jumper out of a Belden RG-58A/U and ended up on a lenght a little less than 6 feet to achieve that X=0. Great video, thanks. By the way, that's without a dummy load.

[@electromechanicalstuff2602]

Really... What happens when u have a load?

[@ozriblit]

What happens when you change the frequency on your CB?

[@electromechanicalstuff2602]

The swr gets worse. That's y u target the center of the band your using. Just like when u tune your antenna. I bet you have either no power and use an antenna tuner

[@ozriblit]

The truest thing you said in this video was “I may be wrong”.

[@electromechanicalstuff2602]

Hahaha. But I'm not

[@ozriblit]

@@electromechanicalstuff2602 you can prove yourself wrong without cutting up any more coax by downloading a good simulator, simNEC comes to mind. Set up a length of 50 Ω coax with a 25 Ω load and a 50 Ω generator Z. Sweep the length between 0 and a bit over 0.5λ and, using the smith chart, see if the SWR changes.

[@jbx907]

it looks as if the coax is invisible form the system when coax are cut in multiple of 1/2 wave

[@jbx907]

@@pamhockens4148 so if we wantr a perfect system, we have to cut the cable odd multiple of 1/2 wavelength?

[@electromechanicalstuff2602]

@@jbx907 yes

[@dannelson8556]

@@jbx907 no you don't this is an old CB wives tale, what happened is some CBer read a ham radio magazine Discussing phasing harnesses which utilized tuned coax stubs and misunderstood what they were reading. Unfortunately this is the end result of the dumbing down of the ham radio service. Nowadays a ham radio ticket isn't worth the paper it's printed on as is clearly demonstrated by this video. The bottom line is if you're not phasing multiple antennas together or doing something like building circularly polarized antennas where one array is fed 90 degrees out of phase from the horizontal array then coax length is irrelevant. Anyone who tells you otherwise has no idea what they're talking about.

[@bill-2018]

Take a look at my posting today about some tests I did, it might make you think again. G4GHB.

[@user-su5sq5ib3i]

You are approaching a fractional resonant frequency of an open stub which is why you were seeing reactants in parallel with the 50 ohm load. Your dummy load is probably fine

[@electromechanicalstuff2602]

Even when I attach the dummy without t same reading tho.

[@KC2SDJ]

Did you read the manual on the antenna analyser? Do you know how to use a dummy load?

[@electromechanicalstuff2602]

Where's all your educational videos? Oh u don't have any cause your not here to help the community only be a troll and criticize it. Gotcha next

[@KC2SDJ]

@@electromechanicalstuff2602 kzbin.info/www/bejne/gZ-5hHl7bNCCh5Isi=3xDbhi6hpKLGo5K8

[@KC2SDJ]

thats not my video but it gets the point across

[@KC2SDJ]

Ive been attaching coax to antennas for years as a Ham radio operator and the only time coax was needed to be tuned was for repeater filters where receive and transmit on a single antenna happens simultaneously. Tuned feedlines only work at one specific frequency where they are tuned.

[@KC2SDJ]

When I say they only work what I meant to say is they are only Tuned at one frequency

[@boricuaengeorgia7332]

And from radio to antena on mobile ?

[@RedNeckSurgeyTech]

So what's the point?

[@1883GotDown]

😊 very nice video bud from Gatekeeper!

[@geoffmcwiggan2814]

Well done Bubby….. Lmao 👍

[@Bens359pete]

I heard it will not show correct swr or x= on MJF 259c unless something inside has been bridged. Any thoughts on this? I have tried tuning a couple coaxes and could not get below x=6

[@EdwardRekas]

How about ...if you connect dummy load to far end of coax feeder line !? Have you try that?

[@electromechanicalstuff2602]

Yes sir I did . And that coax is invisible. And likewise with the coax that's not tuned u can see the reactance of the coax

[@pistolgripp127]

The velocity 👊 for each wire is different giving different readings.! 👍👌✌

[@justcroatboy]

You have to understand the physical fact: Lambda /2 will transfer identical impedance from point A to B, unlike 1/4 lambda which is an impedance transformer! Period!

[@Dallas-Rife-UDX-347-Tennessee]

So the goal is to get the X to as close to zero as possible ?

[@electromechanicalstuff2602]

Basically how I understand it. If u put a perfect antenna it should show 50 ohm's and 0 reactance. So u want your coax to be invisible. And maintain that 0 reactance

[@Dallas-Rife-UDX-347-Tennessee]

@@electromechanicalstuff2602 I’ve watched some other videos as well , but my question is ,, where do I start ? I need an electrically correct length jumper from my radio to amp ,, God knows we’ve all heard every opinion ,, 3/6/9/12 🤷🏼‍♂️,, do I start with a little longer than 12 and keep snipping for X= zero or start with a little longer than 6 and start snipping , in my quest for zero ,, and if I use an MFJ or Rig Expert ,, and I set the frequency at say channel 28 ,, my biggest concern is my reflect and or overall true standing wave SWR dead•key with amp on ,, will be terrible on other channels ,, I custom tuned my 7 element beam with a direct fed 1:1 5K watt balun ,, barefoot ,, I have a 1.0 to a 1.2 from channel one to 40 ,, I’ve recently ran into some reflect issues I think coming back from the antenna , and I’ve been using a 9 foot jumper , then I tried a 6 ,, I’ve tried every size except for a tuned 6 footer or close to it ,, and also haven’t used another tuned 6 foot one from amp to meter ,, with each new adventure ,, I find my standing deadkey SWR getting lower , about 1.2 with amp on which is great ,, but then I see a few hundred watts less output swing ,, so I’ve got my whole project on hold until I get a true reflect meter , to read reflect coming back from my antenna , and an analyzer ,, see my dilemma ,, ?? I’m stuck ,, cause I don’t want to continue and blow my amp up ,, so final question now that I’ve typed a book describing my issue ,, and thanks for reading ,, cause I’m frustrated ,, should I start with 6’ish feet tuning my jumpers , or 9 feet or 12 ?? How does one know where to start ? Is it trial and error after each jumper making ? And if I tune them for channel 28 ,, how broad banded will that be on channel 15 , or 38 ,, etc as far as SWR and reflect goes ?? Any help would be appreciated

[@dannelson8556]

@@electromechanicalstuff2602 LOL OMG And yet another perfect example of the dumbing down of the amateur radio service. If you had to pass a ham a real ham radio test you'd fall flat on your face. Our parroting nothing but old cb wives tales.. Something tells me you're one of these new generation hams who got their license by memorizing the answers to the test

[@bill-2018]

@@Dallas-Rife-UDX-347-Tennessee Look at the Bird 43 manual online. If everything is as close to 50 Ω as possible no problem and no specific lengths of coax needed. Place the SWR meter where you can see it and aim for as low an SWR as possible. I've never in 49 years cut coax to specific lengths. Always good to use ferrite rings on coax too to stop r.f. on the braid which it sounds like you have on your beam. G4GHB.

[@Dallas-Rife-UDX-347-Tennessee]

@@dannelson8556 I sure did 😃 Unless you have something helpful , how about not saying anything at all I’ve learned a lot the last several months Still leaning all the time

[@gruntohseven5803]

Im newb to radio and have a question for you?I needed 2 jumpers(rg400),one from cb to amp,then another from amp to meter.I used my MFJ to make 2 near 6' jumpers,both are at X=0.My swr is high using both 6' jumpers.Should I cut one of them in half and use 2, 3' jumpers?Im thinking that would fix my high swr.Im asking cause l dont want to cut one of my 6' jumpers if its not gonna solve my problem.

[@electromechanicalstuff2602]

Are they tuned 6' jumpers? How high? Antenna is tuned and low when barefoot?

[@bill-2018]

Tune the aerial properly with ferrite rings on the coax. Sorry for commenting if you have already sorted it. G4GHB.

[@bill-2018]

Have a look at my posting today. It might make you think. 73, Bill, G4GHB.

[@RobB_VK6ES]

Every thing you did up to connecting the dummy to the end of the coax was a complete waste of time, but I am sure you had fun all the same. There are legitimate uses for tuned lengths of coax but a simple antenna feed line is not one of them assuming the antenna is close to 50 ohms. A half wave (or a multiple of) will show the impedance at the far end be it a short, open or anything in between. That is why your last test with dummy on end of coax read as 50 ohms (= dummy load 50 ohm). If you were to repeat the same test with any of your other cables the result will be the same. It is this special property of a half wave that is the seed of thought for the fallacy that the feed line needs to be a half wave or multiple. It does not. A quarter wave long coax if left open at one end will theoretically show short but will work perfectly if the end is terminated in 50 ohms. The VSWR on a feed line does not change with length. Bottom line forget all the BS surrounding feed line lengths. the correct length of feed line is just long enough to connect antenna to radio.

[@electromechanicalstuff2602]

@@RobB_VK6ES I did another video of exactly as u said. And had done it before this video without recording it. When I run cables not half wave the swr and impedance change

[@electromechanicalstuff2602]

@@RobB_VK6ES my last video showing what u said is called tuned coax 2.0. no T just dummy load on end of coax each time. I'd love to link it but they will remove comments with links. So look 10 months back in my videos

[@lorenzadickerson9551]

What calculations did you use to make your 1/2 wave rg400

[@electromechanicalstuff2602]

Trial and error. Cut it a few feet long of 1/2 length of my band and started trimming. But there are many out using velocity factor and such. But It'll just save you a few feet of waste when trimming

[@808intheminigrass]

To find coax length : 492 divided by 27.025 (or the channel you favor) times the VF (of coax) .70 = 12.743’ (1/2 wave). It’s math🤓

[@jasonmiller9495]

Lmao I told you I can say it!!!! That was great

[@electromechanicalstuff2602]

Invisible

[@travishorn1847]

Lay your coax out straight and see if there is any difference.

[@electromechanicalstuff2602]

When I did the initial trimming it was not coiled

[@thomaskallmyr]

This is Nice.Escargency Research.......

[@YouTube_User-9]

If you put a dummy load on the end of any length of coax it will read the same 50ohm with the same j/x value as being directly connected to the meter because there are no reflections. Coax lengths should NOT affect your SWR or impedance if your antenna is properly matched because there will be no reflections (or very little). If you are cutting coax lengths to match your system, stop and go back to you antenna and fix the problem. All this cut your coax length to multiples of a wavelength crap is doing it getting your poorly matched antenna's reflections to cancel out do to 180 deg phase cancellation on the way back down the wire, hey now the SWR meter is happy, the finals are happy, but your signal leaving the antenna sucks.

[@electromechanicalstuff2602]

I used the factory 8x wire that was soldered to my Stryker A10 antenna. I used both this fmj along with a nano vna to tune the antenna. I got it as low as possible with my lowest point at ch 20. I achieved 1.3 SWR at the lowest point and 1.45 at the ends of the dip. It's tuned is what I'm saying. But once I put the tuned coax on now my lowest SWR point is 1.1 and highest is 1.25. yes even with the dummy connected to the end of the coax I get the same readings. This is absolutely a complicated topic I am still learning about. I understand smith graph and that it should not effect swr but in a mobile application the car is part of the antenna and this is sometimes the only thing you can do to "tune" the antenna that is already itself tuned

[@YouTube_User-9]

@@electromechanicalstuff2602 I have the Stryker mag mount on my car. I can get it to about 1.1:1 on 11m. Maybe try moving it around a little if you cant adjust the length of the whip to get it lower. If yours in not a mag mount check your RF ground connections. Or your car does not have a good ground all the way around and you might benefit from ground straps connecting the trunk lid and hood and things of that nature. Might get you a better match.

[@electromechanicalstuff2602]

That's what I have now already on e I changed to a tuned rg400 1/2 wavelength. Yes mag mount now. Soon I'll be installing a breed mount puck. I moved it around a ton till I found the best spot but it didn't change much with location. No doubt my car panels are not properly grounded to each other. The car is the ground poise and can effect the swr greatly

[@RC-Heli835]

So you need a calculated half wave coax to tune the antenna with and after that coax length doesn't matter?

[@YouTube_User-9]

@@RC-Heli835 You can use any length you need to get from your antenna to your radio. As long as the antenna is tuned to 50 ohms or at least very close for the middle of the band you want to tune ( or where you work it the most) it will be really close to a perfect match no matter the length of 50 ohm cable. Cable length can "tune" an antenna but it's not the right way and is only making the radio happy, the antenna is still out of tune.

[@richardcallihan9746]

Should have waited till your little buddy went to bed.

[@electromechanicalstuff2602]

Nah. Hes learning

[@arildoaparecidocosta5729]

Ótimo vídeo gualidade total Cabo ok bazuka Foz do Iguaçu pr Brasil 🇧🇷🦈 73 🇧🇷

[@germanjohn5626]

Wow so much misunderstanding of the physics, calling a dummy load an antenna and then trying to use a 50 ohm resistive load or an open to show differences in coax is ignorant lol. especially with a Mighty Fine Junk as test equipment. All this can be classified as junk science , I guess that is what you get from someone who has no formal education in the matter.

[@electromechanicalstuff2602]

Wow thanks for the constructive criticism.... There's a reason I said I don't know please correct if wrong. And commenters have said it's correct. All I got out of your comment is that your a very unhappy individual who will most likely die alone because your such a miserable person. God bless and good luck with your life Edit u won't die alone you'll be surrounded by cats

[@imken2392]

@@electromechanicalstuff2602 He just doesn't understand...People are thinking in volts, amps and ohms...once RF wave propagation through a wire is introduced, things change.

[@KC2SDJ]

CB guys are nuts, read a good antenna book before you spend money on equipment you dont know how to use

[@t77chevy]

An open quarter wave coax will reflect the signal back towards the dummy load exactly out of phase and cancel the reading “ 1/4 = 90 degree phase to open end , reflects back 1/4 90degree to dummy load for a total of 180 degrees out of phase which cancels it out , easily see this on a smith chart Your dummy load had small reactance value which should change mildly between the 1/2 wavelength and 1/4 wavelength coax when connected to its far end “ not T in “ , personally rig expert is far better for making stubs than your mfj

[@electromechanicalstuff2602]

Did u watch the entire video. I did infact put the dummy at the end of the coax and got the exact same result. The reason I used the t is because when your tuning the coax u have to cut to tune and I'm not throwing away 10 silver connections. Just to keep the load at the end when the results are the same.

[@ericdee6802]

@@electromechanicalstuff2602 get rid of the "T" fitting

[@sirmister4411]

This is too funny Wow you really have no clue about rf just by the way you are testing this I’m glad your not an engineer for a radio station.

[@electromechanicalstuff2602]

@@sirmister4411 I'd never want that job.... It doesn't pay enough money. I have 1.01: 1 match on 5 different stations all with over 2,000 watts. So I'm doing something right. Have fun and remember if it says high voltage YOU should definitely give it a touch

[@nikn2621]

I don't like your expensive instrument !

[@bill-2018]

Let's lay this to rest! I already knew this but for disbelievers I have today run some tests on coax. The length of coax makes no difference because everything is matched to 50 Ω, the tx, coax and load are all 50 Ω. Tx FT817ND on f.m. for a carrier to see on the oscilloscope, Beckman Industries model 9020, 50 Ω dummy load and various coax lengths. I used 21.200 MHz as the 'scope is not happy above 25 MHz. DL on 4" length of coax. Test directly with 50 Ω at tx. 3.4 Volts. Amendment; the 'scope was on X10 so it's 34 Volts. Test with 20" coax plus 4" to DL. 3.4 Volts. Test with 38" coax plus 4" to DL. 3.4 Volts. Test with 58" coax plus 4" to DL. 3.4 Volts. Test with 20" coax to SWR meter with DL on 4" coax. Zero movement. Test with 38" coax to SWR meter with DL on 4" coax. Zero movement. Test with 38" coax to SWR meter with DL on 20" coax plus 4" coax. Zero movement. Test with 58" coax to SWR meter with DL on 4" coax. Zero movement. Where is the need for this magical ½λ of coax? The SWR meter can go anywhere in the coax, it's handy to see inside the shack. 73, Bill, G4GHB.

[@electromechanicalstuff2602]

Can you video this and post it. Plus the biggest concern is not just the 50 ohm it the inductance and capacitance that affects the tuning of the circuit that seems to be the most important part. I'll try to find some random sections of coax and do a similar tests on my bird dummy load using my VNA and mfj in the next few days

[@bill-2018]

@@electromechanicalstuff2602 I can't video it as I've only an old camera and not much memory on it. Yes, it's interesting, do give it a go. I thought I'd put it on here and it might get people to investigate it. I've never had problems in 49 years of transmitting with home brew gear and commercial gear. It's about getting as close as possible to 50 Ω at the aerial. I've used 1.5:1 when my long wire was too short for the tuner to cope but wouldn't like to go above. Bird say about a 50 Ω system and how the meter can go anywhere if all is well. 73, G4GHB.

[@electromechanicalstuff2602]

@@bill-2018 I agree the meter can go anywhere when your using a tuner. The tuner counteracts the inductance and capacitance of the coax and antenna if they are not perfect

[@bill-2018]

@@electromechanicalstuff2602 Yes, a tuner is needed for a long wire etc. Again I say not so much the coax.

[@electromechanicalstuff2602]

@@bill-2018 k. I know u make your antenna out of random wire. Buy a cheap 50 ohm antenna. Band specific. Get rid of the tuner and tell me what happens. The reason you've never had issues is because u have a tuner. Point blank period. I started without a tuner and this is what is necessary when you don't have a tuner running any kind of power. Or you have to tune your amplifiers output circuit to match you antenna circuit. That includes the coax. Do you own or have you ever used a VNA, or any sort of antenna analyzer? I have several of both and all the equipment tells me a different story than I've been doing it forever with an antenna tuner and never had a problem. I doubt I'll ever convince you to go out and buy a $500 complicated piece of testing equipment that can display smith charts and frequency nodes. But I did. So I'm going off the information my equipment is telling me for now.