cutting/nulling you coax for frequency for accurate readings.

[lilbump]

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.

[shanerorko]

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.

[eiju]

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.

[easternNorthCarolina]

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?

[geranwilson]

Thank you sir it helped a tremendous amount

[clintd]

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.

[muhwildan]

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?

[muhwildan]

is the same, about measure matching cable. with TEE connector + dummyload.
and then looking for about SWR with lower value.

[Bond]

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.

[alexfaught]

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.

[Stevef-skjc]

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..

[truthfilterforyoutube]

If you BUY ONE THESE RigExperts ....Make sure you have a 50 Ohm Dummy load as you will need one when doing the initial "self test", in the " Tools", function to perform this operation....you can't get at "tools functions". without doing the complete 3 stage test upon initial setup

[craig_sez]

If you calibrated your analyzer with a load/short/open and then your golden..Analyzer doesnt see coax when tuning..

[truthfilterforyoutube]

What people don't realize is that the coax is part of your " Ears". You listen with ground part of that ground is the YES you want the coax to be resonant at your preferred frequency.... I believe this method will also bring you closer to the Magical " 60" return loss number, thus improving antenna efficiency !

[franciscolopez]

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.

[bigsouthranchin]

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!

[seeharvester]

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.

[kfqbw]

question how to trim base station coax length at 100' for a frequency wa aa55 zoom an
alizer

[ChristiannTyler]

I cut mine to around 6.5ft and its resonance is 30649 so I basically wasted this section of coax? Since trimming it will only increase its resonant frequency.

[tractorman]

Thanks for the video. Do you also tune your main run of coax too?