This is a common practice in CB land, but doesn't actually do much. The SWR meter will be tricked anyway as coax has loss. Infact some people will say a certain antenna works better with X amount of coax, but all they're doing is putting heat into the coax to make the SWR better. But what happens to the wave length inside the SWR meter? What the radio waves stop and say "hey that coax is tuned so we better skip this SWR meter"? The meter has wire inside. You know what is easier? Take that rig expert VNA and measure the SWR at the antenna and get it low, then use a tuner to bring in the last bits of SWR, most radios have a 3:1 tuner for this reason. Then hey presto you can use any length of coax. Coax tuning is used in cavity duplexers, yagi stack matching and vertical array phasing lines. The CB world has just taken this practice and put it to use for no reason in feed lines. Thanks. Shane VK1NME.
@757boulderbuilt4 yea maybe if I try and run 1000w through RG58 lol. I use M&P 10mm coax or LMR400, I recently bought a jumper made from Timesmicrowave genuine LMR400 and it has 8 clip on ferrites, works great.
The whole Idea is getting the voltage off or in the coax gone! Just like using a Balun on your antenna for big watts! Not this "Oh I run 1kw crap!" You start running 10kw and so forth and get in that pocket you will learn this does work! Also sort of like input tuning or building a stub, its got to be tuned to work CORRECTLY!!! 757 Do your thing Bro!!!!@@shanerorko8076
I believe this is the correct method for finding the exact quarter wave length(at frequency X). To find the exact half wave length(at frequency X) you would need to short the open end.
What ur doing is basically the same as cutting and shortening an EFHW antenna, of course the resonant frequency is going shift but the impedance of that piece of coax still remains @ approx. 50 Ohm. Attach that coax to a resonant antenna then start making it shorter, the resonant point of the antenna remains the same but the coax getting shorter introduces less feedline loss. So to recap, the coax in your experiment at a specific length is an antenna, the outer braid and the inner act as Ground and Conductor, in snipping bits off all ur doing is shortening an antenna hence why the resonant frequency of the meter changes.
In the end when everything is up and running my swr is absolutely flat at very high power output. I have personally never achieved this without cutting my coax to resonate lenth for the band with a direct feed mono band antenna. The swr would always rise above 1000 watts before doing so,,take it for what you will😉
After many many years of working as a Radio Engineer, I agree with you. Coax does need to be trimmed to multiples of the wavelength it is used on. The main reason people do not think you have to is because they see it as a piece of wire, they do not know about RF. I have always done this on professional installations.
Well you need to go back to engineering school. Coax tuning is used in cavity duplexers, yagi stack matching and vertical phased arrays ect. It's not needed in feed lines unless you have a poorly designed antenna. Infact some antennas like the Zepp and J pole which is just a Zepp use twin wire feed lines cut a a wave multiple. But for feedline duties on coax this is utterly useless. Thanks. Shane VK1NME.
Dipoles and an inverted vee here and I've never trimmed coax. This guy is carefully and accurately trimming his coax then joins it together via an SWR meter to a jumper coax to his radio. No longer his magical length of coax, he's made it longer. G4GHB.
thank your video. so that main, effect for matching frequency in cable coax. about X. ( reactancy). looking for X=0. for matching cable is the correct?
If you put a 50 ohm resistor on the end of the cable, does it change the resonant frequency? I’ve learned if your antenna is tuned correctly that the coax length to the antenna input does not matter. Perhaps More important between amplifiers? I did have to change my coax from amp to meter to the shortest length as possible to keep my meter from doing crazy things.
I look at it this way. If you have the means to measure the length of your coax and cut it to a preferred multiple, why not? It certainly doesn't hurt anything.
757 does one need to do this practice for the transmission line going to the antenna? 200 ft of coax is what I’m dealing with. What’s your recommendation? Thanks! 73’s. Cobra 818 in the Mag!
@@bigsouthranchin Right okay. I should have asked what type of coax. I'm thinking of my very short RG58 with a calculated figure of 0.6 dB for this length at 28 Mhz. No tower. 73.
So RG 213, with a vel. factor of .66, @ 27.385 Mhz, that would be 11.854' (11' 10 1/4" for a half wave length) x 17 half wave lengths = 201' 6 1/4", right?
On uhf this trick cleans up a lot of errors especially with long lengths of cable.. if you dont do this and you are changing cables [ length and brand ] you will get different measurements each time.. so tune your cable..If you have daul or quad band radios.. i e a wouxun the output impedance is 35 ohm on one of the bands so a 50ohm system isnt too good..
How do you do this with an AA-600? There doesn't seem to be a feature that simply tells you the resonant frequency in the R/X graph so you have to do it the hard way. The manual says that a resonant frequency is where X reactance is at 0, but there are several points where this happens along a span of frequencies. Can anyone explain step by step how to find a resonant frequency with nothing but an R/X graph?
Im curious as to how you got the analyzer to show resonance at the bottom of the screen? I can go to the r,x setting on mine and it does not display resonance at the bottom.
I had the same issue. Use the up arrow to zoom out. Run it again. Then it will appear if the range is wide enough. And will remain after you zoom back in...
I got a question for you everyone says different when I ask.. in a mobile I'm running a kicker and a 4 pill what would be the correct length coax to start with. Currently I have a 3' jumper between my radio and kicker and a 9' between my kicker and 4 pill the 18' to my antenna from my big box
Keep in mind that you are cutting your coax to resonance to make your Vswr meter read correctly, on a 50 ohm node. The output of your radio is 50 ohms, so is the input to your amp if built correctly. A nulled 1/2 wave jumper from the radio to the amp will match at 50 ohms and your radio's Vswr meter will read correctly. Take that 1/2 wave jumper and connect it to your antenna with the analyzer at the other end. Tune your antenna for reactance = 0 or as close as you can get. Vswr and resistance usually follows unless you've got a ground or RF bonding issues. The output of your amp is 50 ohms and so now is your antenna, or really close. Make another 1/2 wave section to go from the amp to the antenna. If the antenna is farther away than 1/2 wavelength use a multiple of 1/2 wavelength. I tend to go with odd multiples to keep everything in phase. I use Messi & Paoloni ultraflex 13 for the base and Messi & Paoloni ultraflex 10 for the mobile. Great stuff. Basically zero loss in 1/2 wave lengths and only .4 db loss over 100 feet with a velocity factor of .86. We can't tell you the specific length of your coax because we don't know what coax it is or the velocity factor.
Hey Nick I got a question that I've been wrestling with. If I were to put together a run of 5/8 hardline to a short run of lmr400 can I null it all together? Diffrent velocity factors. Or would i have to null them separate?
Was that coax you're trimming connected to the analyzet and can I do the same to tune my main antenna coax and jumppers with my MFJ 269? Sure would appreciate a reply. Thank you sir.
Get rhe tuner or couple out at the antenna end,,,so many people have inefficient antenba and coax sysyem no realising its all relevant to each other,,,it not just stick good coax on and forget about it,,physics doesn't work like that,,,good video.
Most of the people that think nulled jumpers are a myth don't know anything about power tuning systems with a reflect meter vs using their SWR meter. Then again, most of those people aren't running enough power to need to worry about it, so their set of 'facts' works for them. I just wish they'd shut up about it and stop acting so high and mighty about their random 9 inch jumpers and barefoot radios with an SWR of 1.01.
The stupid thing about this is if the load impedance is the same as the the radio impedance, the SWR will be same along the entire length of a feedline with the same characteristic impedance. If the load doesn't match, you will get different SWR readings (let's separate meter trickery here) because the coaxial is now behaving as an impedance transformer. So it's sort of like six of one, and half a dozen of the other I know you're doing this to prove some point, but I will still say, since you have such a sophisticated piece of equipment in that analyser, why not use it to measure your antenna impedance and be done with it? If you're still so worried about the coax, run multiples of a half wavelength and the system will ignore it, whatever impedance coax. But hang on, those shitty amps, surely they don't have a 50 ohm output or input impedance. You wouldn't assume anyway. So what's the easiest thing to do? Tune the antenna to the amp, and cut a patch lead to the radio as a transformer.
@@757boulderbuilt4 Why not use an r.f. detector at the aerial as I have done for many years? I had no SWR meter for about 40 years and only built one about 10 years ago. It works out, maximum r.f. at the aerial corresponds to a low SWR. I never trimmed any coax to length. In fact it has always been said to put the SWR meter at the aerial. 73. G4GHB
@Bill Kitchen I'm sorry Bill that your still missing my point , this is an age old argument/discussion and that's why I made a short video on the matter,,also because I don't care to rehash the matter👋
Trimming coax inch by inch and then connect it through an SWR meter to a jumper coax to the radio You do realise it is all now one longer length of cable so all that trimming was pointless. G4GHB.
@@757boulderbuilt4 Each length? Do you think the coax stops at the SWR meter and is isolated from the other side which is another new side of coax? It's two coax cables joined together as one. Even if what you say about each length is true what about the length of the SWR meter. Oh I forgot, that's isolated so doesn't get included. G4GHB.
@@757boulderbuilt4 What do you mean by pass through tune? You stated before that if each length is nulled it will stay good throughout, do you null both coax to the aerial and the jumper lead? If not the jumper, why not? It's impedance will change from 3 foot to 6 foot. Does that not bother you the transmitter sees it? Only the 'aerial side' matters? It's because it's all nonsense. The two cables are not independent of each other. It's one cable with an indicating device placed in it. Check with a multimeter, the braids are connected as are the inner conductors. Check with a VNA and see your magical carefully trimmed half wave coax has disappeared.
I see no comment so I guess you either tried the multimeter and/or VNA and found I'm right or you haven't bothered in case you're wrong. Open your SWR meter and look, both SO239 are connected together with a wire and the outer braids connected together by metalwork. There is no magical half wave coax. It's gone and joined the jumper lead as one cable. G4GHB.
This is a common practice in CB land, but doesn't actually do much.
The SWR meter will be tricked anyway as coax has loss.
Infact some people will say a certain antenna works better with X amount of coax, but all they're doing is putting heat into the coax to make the SWR better.
But what happens to the wave length inside the SWR meter? What the radio waves stop and say "hey that coax is tuned so we better skip this SWR meter"? The meter has wire inside.
You know what is easier? Take that rig expert VNA and measure the SWR at the antenna and get it low, then use a tuner to bring in the last bits of SWR, most radios have a 3:1 tuner for this reason.
Then hey presto you can use any length of coax.
Coax tuning is used in cavity duplexers, yagi stack matching and vertical array phasing lines.
The CB world has just taken this practice and put it to use for no reason in feed lines.
Thanks.
Shane VK1NME.
In higher wattage situations you might end up with a different opinion 😉
@757boulderbuilt4 yea maybe if I try and run 1000w through RG58 lol.
I use M&P 10mm coax or LMR400, I recently bought a jumper made from Timesmicrowave genuine LMR400 and it has 8 clip on ferrites, works great.
The whole Idea is getting the voltage off or in the coax gone! Just like using a Balun on your antenna for big watts! Not this "Oh I run 1kw crap!" You start running 10kw and so forth and get in that pocket you will learn this does work! Also sort of like input tuning or building a stub, its got to be tuned to work CORRECTLY!!! 757 Do your thing Bro!!!!@@shanerorko8076
By the way, I don't hit and hide my hand! MR2020 Backwoods of Georgia
I believe this is the correct method for finding the exact quarter wave length(at frequency X). To find the exact half wave length(at frequency X) you would need to short the open end.
I was wondering how you would go about tuning a half wave of coax,thank you
What ur doing is basically the same as cutting and shortening an EFHW antenna, of course the resonant frequency is going shift but the impedance of that piece of coax still remains @ approx. 50 Ohm. Attach that coax to a resonant antenna then start making it shorter, the resonant point of the antenna remains the same but the coax getting shorter introduces less feedline loss. So to recap, the coax in your experiment at a specific length is an antenna, the outer braid and the inner act as Ground and Conductor, in snipping bits off all ur doing is shortening an antenna hence why the resonant frequency of the meter changes.
In the end when everything is up and running my swr is absolutely flat at very high power output. I have personally never achieved this without cutting my coax to resonate lenth for the band with a direct feed mono band antenna.
The swr would always rise above 1000 watts before doing so,,take it for what you will😉
I have an mfj 249 now my question is now when doing this I do need to get X as close to zero as possible along with the frequency I want to operate?
After many many years of working as a Radio Engineer, I agree with you. Coax does need to be trimmed to multiples of the wavelength it is used on. The main reason people do not think you have to is because they see it as a piece of wire, they do not know about RF.
I have always done this on professional installations.
Well you need to go back to engineering school.
Coax tuning is used in cavity duplexers, yagi stack matching and vertical phased arrays ect.
It's not needed in feed lines unless you have a poorly designed antenna.
Infact some antennas like the Zepp and J pole which is just a Zepp use twin wire feed lines cut a a wave multiple.
But for feedline duties on coax this is utterly useless.
Thanks.
Shane VK1NME.
Dipoles and an inverted vee here and I've never trimmed coax.
This guy is carefully and accurately trimming his coax then joins it together via an SWR meter to a jumper coax to his radio.
No longer his magical length of coax, he's made it longer.
G4GHB.
is the same, about measure matching cable. with TEE connector + dummyload.
and then looking for about SWR with lower value.
Thank you sir it helped a tremendous amount
thank your video.
so that main, effect for matching frequency in cable coax. about X. ( reactancy).
looking for X=0. for matching cable
is the correct?
Yes, if you look at the blue line, that represents the X. At the top of the grid it was showing 0.47 in blue numbers, which is very close.
If you calibrated your analyzer with a load/short/open and then your golden..Analyzer doesnt see coax when tuning..
If you put a 50 ohm resistor on the end of the cable, does it change the resonant frequency? I’ve learned if your antenna is tuned correctly that the coax length to the antenna input does not matter. Perhaps More important between amplifiers? I did have to change my coax from amp to meter to the shortest length as possible to keep my meter from doing crazy things.
if your meter is doing crazy things have you r.f. on the braid?
Do you use ferrite rings?
G4GHB.
I've actually talked to you on 38LSB, it's pretty surreal that this video came up in my youtube feed! CJ 323 New Jersey waving a hand.
It's no coincidence.
I look at it this way.
If you have the means to measure the length of your coax and cut it to a preferred multiple, why not? It certainly doesn't hurt anything.
757 does one need to do this practice for the transmission line going to the antenna? 200 ft of coax is what I’m dealing with. What’s your recommendation? Thanks! 73’s. Cobra 818 in the Mag!
Yes use a resonant length
200 foot of coax. How much loss is there in that? There must be 6 dB or so. That's a lot to lose.
@@bill-2018 rg213 close to 1db per 100 foot. It’s not that bad. But you got to if your tower is 100 foot tall! 73s!
@@bigsouthranchin Right okay. I should have asked what type of coax. I'm thinking of my very short RG58 with a calculated figure of 0.6 dB for this length at 28 Mhz. No tower.
73.
So RG 213, with a vel. factor of .66, @ 27.385 Mhz, that would be 11.854' (11' 10 1/4" for a half wave length) x 17 half wave lengths = 201' 6 1/4",
right?
On uhf this trick cleans up a lot of errors especially with long lengths of cable.. if you dont do this and you are changing cables [ length and brand ] you will get different measurements each time.. so tune your cable..If you have daul or quad band radios.. i e a wouxun the output impedance is 35 ohm on one of the bands so a 50ohm system isnt too good..
question how to trim base station coax length at 100' for a frequency wa aa55 zoom an
alizer
How much real impedance of the coax?
Excellent demonstration
How do you do this with an AA-600? There doesn't seem to be a feature that simply tells you the resonant frequency in the R/X graph so you have to do it the hard way. The manual says that a resonant frequency is where X reactance is at 0, but there are several points where this happens along a span of frequencies. Can anyone explain step by step how to find a resonant frequency with nothing but an R/X graph?
Thanks for the video. Do you also tune your main run of coax too?
Yes
Im curious as to how you got the analyzer to show resonance at the bottom of the screen? I can go to the r,x setting on mine and it does not display resonance at the bottom.
I had the same issue. Use the up arrow to zoom out. Run it again. Then it will appear if the range is wide enough. And will remain after you zoom back in...
How do you set it up to check or tune your antenna in 10mts ?
Excellent Nick
I got a question for you everyone says different when I ask.. in a mobile I'm running a kicker and a 4 pill what would be the correct length coax to start with. Currently I have a 3' jumper between my radio and kicker and a 9' between my kicker and 4 pill the 18' to my antenna from my big box
Keep in mind that you are cutting your coax to resonance to make your Vswr meter read correctly, on a 50 ohm node. The output of your radio is 50 ohms, so is the input to your amp if built correctly. A nulled 1/2 wave jumper from the radio to the amp will match at 50 ohms and your radio's Vswr meter will read correctly. Take that 1/2 wave jumper and connect it to your antenna with the analyzer at the other end. Tune your antenna for reactance = 0 or as close as you can get. Vswr and resistance usually follows unless you've got a ground or RF bonding issues. The output of your amp is 50 ohms and so now is your antenna, or really close. Make another 1/2 wave section to go from the amp to the antenna. If the antenna is farther away than 1/2 wavelength use a multiple of 1/2 wavelength. I tend to go with odd multiples to keep everything in phase. I use Messi & Paoloni ultraflex 13 for the base and Messi & Paoloni ultraflex 10 for the mobile. Great stuff. Basically zero loss in 1/2 wave lengths and only .4 db loss over 100 feet with a velocity factor of .86. We can't tell you the specific length of your coax because we don't know what coax it is or the velocity factor.
@@imken2392 I purchased a rig expert and am now in tune and running lmr 400 gained almost 100 watts
Thank you
Hey Nick I got a question that I've been wrestling with. If I were to put together a run of 5/8 hardline to a short run of lmr400 can I null it all together? Diffrent velocity factors. Or would i have to null them separate?
Sure no problem
Was that coax you're trimming connected to the analyzet and can I do the same to tune my main antenna coax and jumppers with my MFJ 269? Sure would appreciate a reply. Thank you sir.
I'm not familiar with the mfj-269
Excellent
Get rhe tuner or couple out at the antenna end,,,so many people have inefficient antenba and coax sysyem no realising its all relevant to each other,,,it not just stick good coax on and forget about it,,physics doesn't work like that,,,good video.
Great video
Thanks!
They can't handle the truth...take it easy on them...as they don't what they are talking about....great video...
Most of the people that think nulled jumpers are a myth don't know anything about power tuning systems with a reflect meter vs using their SWR meter. Then again, most of those people aren't running enough power to need to worry about it, so their set of 'facts' works for them. I just wish they'd shut up about it and stop acting so high and mighty about their random 9 inch jumpers and barefoot radios with an SWR of 1.01.
Good video
Well that is the truth.
1963 Jamaica
The stupid thing about this is if the load impedance is the same as the the radio impedance, the SWR will be same along the entire length of a feedline with the same characteristic impedance. If the load doesn't match, you will get different SWR readings (let's separate meter trickery here) because the coaxial is now behaving as an impedance transformer. So it's sort of like six of one, and half a dozen of the other
I know you're doing this to prove some point, but I will still say, since you have such a sophisticated piece of equipment in that analyser, why not use it to measure your antenna impedance and be done with it? If you're still so worried about the coax, run multiples of a half wavelength and the system will ignore it, whatever impedance coax. But hang on, those shitty amps, surely they don't have a 50 ohm output or input impedance. You wouldn't assume anyway. So what's the easiest thing to do? Tune the antenna to the amp, and cut a patch lead to the radio as a transformer.
Those shitty amps are indeed the problem. I disconnected mine. Don't really need it anyhow.
Get ready for all of the hater comments. Lol
I agree with you
You've made an open circuit stub. Of course the frequency changes.
Apparently you missed the point but that's fine.
@@757boulderbuilt4 Why not use an r.f. detector at the aerial as I have done for many years? I had no SWR meter for about 40 years and only built one about 10 years ago. It works out, maximum r.f. at the aerial corresponds to a low SWR. I never trimmed any coax to length. In fact it has always been said to put the SWR meter at the aerial.
73. G4GHB
@Bill Kitchen I'm sorry Bill that your still missing my point , this is an age old argument/discussion and that's why I made a short video on the matter,,also because I don't care to rehash the matter👋
Trimming coax inch by inch and then connect it through an SWR meter to a jumper coax to the radio
You do realise it is all now one longer length of cable so all that trimming was pointless.
G4GHB.
If each lenth is nulled it will stay good throughout. But there are some , especially hams using the same coax for all bands that will never get it.😉
@@757boulderbuilt4 Each length?
Do you think the coax stops at the SWR meter and is isolated from the other side which is another new side of coax?
It's two coax cables joined together as one.
Even if what you say about each length is true what about the length of the SWR meter. Oh I forgot, that's isolated so doesn't get included.
G4GHB.
If equipment is made correctly with a proper pass through tune ( capaitance) it doesn't matter
@@757boulderbuilt4 What do you mean by pass through tune?
You stated before that if each length is nulled it will stay good throughout, do you null both coax to the aerial and the jumper lead?
If not the jumper, why not? It's impedance will change from 3 foot to 6 foot. Does that not bother you the transmitter sees it? Only the 'aerial side' matters?
It's because it's all nonsense.
The two cables are not independent of each other. It's one cable with an indicating device placed in it. Check with a multimeter, the braids are connected as are the inner conductors.
Check with a VNA and see your magical carefully trimmed half wave coax has disappeared.
I see no comment so I guess you either tried the multimeter and/or VNA and found I'm right or you haven't bothered in case you're wrong.
Open your SWR meter and look, both SO239 are connected together with a wire and the outer braids connected together by metalwork.
There is no magical half wave coax. It's gone and joined the jumper lead as one cable.
G4GHB.