tuned coax 2.0

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Күн бұрын

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@marcstrauven4697 9 ай бұрын

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

@fredflintstone9963 10 ай бұрын

PL259 connectors shouldn't be allowed near any measuring instrument. They are from the early 1930s and were a joke back in the 1960s, let alone today.

@electromechanicalstuff2602 10 ай бұрын

Then do it with type N and I bet u my ridiculous salary it's the same results.

@fredflintstone9963 10 ай бұрын

@@electromechanicalstuff2602 You seem to have missed my point: it's just basic RF engineering to use connectors that were actually DESIGNED as a constant impedance components when making precision measurements. There are enough sneaky variables in RF engineering without volunteering more.

@ozriblit 3 ай бұрын

You mentioned that one of the pieces of coax has a velocity factor of 1. That can’t happen for anything other than free space. Coax cable. When you look at the specs for coax you will see a number for capacitance/unit length (ft or metres) and the same for inductance. These were what you were reading on both instruments. Also for coax, there are two well understood properties. If a coax is 1/2 λ at a given frequency, the termination at one end is repeated at the other. That is to say that an open will be seen as an open and a short as a short. If the coax is 1/4 λ at a given frequency, the termination at one end is reversed at the other. At the two extremes, an open will be seen as a short and vice versa. These repeat every even multiple for λ/2 and every odd multiple for λ/4. In addition, a coax less than λ/4 behaves as an inductor, over that as a capacitor. This repeats every λ/2. Your VNA has a smith chart. It will show the phase change as you sweep the frequency. Try the λ/4 piece with both an open and a short. You can also try the two short pieces to a T connector and the s11 and s21 ports on the VNA, and calibrate the through. Connect the other pieces of coax to the T and watch the effect when you vary the load. Try the dummy load and some resistors if you have any.

@KINGLOWNESS 11 ай бұрын

What setting, mode or graph do you use on the vna when trimming?

@electromechanicalstuff2602 11 ай бұрын

I used the MFJ -259D when I made my jumpers. I'll have to actually try to do it on the VNA but I would assume I'd set it for the same as in the video resistance and SWR. Use a T Put the dummy load on one side of the T. The VNA one one side of the T. The coax your tuning on the last side. Obviously you'd have to have one end soldered on. The cut end would just be open/cut. But not shorted. As you cut pieces off you can see the SWR get lower and lower and the resistance gets closer and closer to match your dummy loads original resistance.

@KINGLOWNESS 11 ай бұрын

@@electromechanicalstuff2602 Try the "Phase" view that's what I used for least reactance... There may be a better way that's what I'm trying to figure out 😂😂😂

@KINGLOWNESS 11 ай бұрын

@@electromechanicalstuff2602 I used an open stub got to the point where I was trimming literally 1/8 of an inch at a time. The last trim on one started going up negligibly so I of course stopped.... I was in quite the rush to get my mobile setup done but I'm going to have to at least redo some jumpers

@davewood4604 10 ай бұрын

The characterisic impedance of the coax will affect SWR, as will the impedance of the connectors, as will the load. Unless you are using a fixed frequency there really is no point using a tuned length of coax. Every change in impedance for example from a piece of coax at 48ohm to a 49ohm load will increase SWR and so on. A longer wire will introduce more loss and lower the SWR if the bad SWR is at the far end. There are so many variables. Also there are some excellent PL-259's out there for example Messi & Paoloni, these are supperb but most are crap.

@electromechanicalstuff2602 10 ай бұрын

I agree with most of what u said. However I still believe it's worth doing if you are just a single band station. Set the length pending your center frequency in your band or your favorite frequency and you can avoid any physical input output tuning on your equipment.

@mcconja 8 ай бұрын

@@electromechanicalstuff2602 I agree why not make the cable so your meters are happy. A very good RF engineer told me one time, if it makes you feel better, tune, the coax to get your antenna tune. Once that’s done, don’t worry about the length, but if you use your meters to tune your antenna, the coax should be cut to a null.

@electromechanicalstuff2602 8 ай бұрын

@@mcconja u can put an SWR/ power meter anywhere u want and it won't change the tune or what your meters see. But in between radio and amp the length should be nulled.