A SWR conundrum

[northern35s]

Thanks for playing along chaps, once again thanks to Steve Hunt, G3TXQ, for posing the original question.

The best VSWR is 1.0:1
The worst case VSWR is 1.9:1

Here's the calculation for the worst case scenario:

The impedance at the end of the first is 52*52/50 = 54.1 Ohms
That's then transformed by the second to 48*48/54.1 = 42.6 Ohms
Then that's transformed to 52*52/42.6 = 63.5 Ohms
etc etc.

You end up after eight with 26.3 Ohms and an SWR of 1.9:1

For the best case scenario each 1/2WL is a repeater of the lead, no transformation takes place as it would do with a 1/4WL section, this latter phenomenon was also discussed in another thread on here.

It is interesting to know this, and given a couple of coax connections, and maybe a mixture of age and supplier, it's possible to have a situation where you may never be happy with your VSWR, have you ever measured the characteristic impedance of your coax runs and patch leads, I know I haven't

 

[RADIOOMAN]

Thanks for playing along chaps, once again thanks to Steve Hunt, G3TXQ, for posing the original question.

The best VSWR is 1.0:1
The worst case VSWR is 1.9:1

Here's the calculation for the worst case scenario:

The impedance at the end of the first is 52*52/50 = 54.1 Ohms
That's then transformed by the second to 48*48/54.1 = 42.6 Ohms
Then that's transformed to 52*52/42.6 = 63.5 Ohms
etc etc.

You end up after eight with 26.3 Ohms and an SWR of 1.9:1

For the best case scenario each 1/2WL is a repeater of the lead, no transformation takes place as it would do with a 1/4WL section, this latter phenomenon was also discussed in another thread on here.

It is interesting to know this, and given a couple of coax connections, and maybe a mixture of age and supplier, it's possible to have a situation where you may never be happy with your VSWR, have you ever measured the characteristic impedance of your coax runs and patch leads, I know I haven't

Thanks 'northern35s', that was fun, for me, for a couple of the others, not so much.
It's just a good thing I am not smart enough to calculate with those (+J) and (-J) thingys; As suggested by someone else......lol

 

[bob85]

i think you already knew who was gonna get it, who would try obfuscation by introducing imaginary parts and who would make up their own laws of physics before you posed the question

 

[northern35s]

i think you already knew who was gonna get it, who would try obfuscation by introducing imaginary parts and who would make up their own laws of physics before you posed the question

:blushing:

 

[hookedon6]

...each 1/2WL is a repeater of the lead, no transformation takes place as it would do with a 1/4WL section,/QUOTE]
that is correct,... as far as it goes,.... BUT,......in the overall feedline it is
absolutely WRONG!!! a little bit of knowledge is dangerous.

you are saying 2 1/4 wl 48 ohm sections connected to 2 1/4 wl 52 ohm sections do NOT see an impedance mismatch?

the mismatch is at the 48-52 connection,...... NOT the 48-48 or 52-52 ohm connection,.................... DUH!!!

you and your running mate don't have a clue,

both of you don't even know where to put a meter in the feedline..... sad

 

[northern35s]

...each 1/2WL is a repeater of the lead, no transformation takes place as it would do with a 1/4WL section,/QUOTE]
that is correct,... as far as it goes,.... BUT,......in the overall feedline it is
absolutely WRONG!!! a little bit of knowledge is dangerous.

you are saying 2 1/4 wl 48 ohm sections connected to 2 1/4 wl 52 ohm sections do NOT see an impedance mismatch?

the mismatch is at the 48-52 connection,...... NOT the 48-48 or 52-52 ohm connection,.................... DUH!!!

you and your running mate don't have a clue,

both of you don't even know where to put a meter in the feedline..... sad

If you refrained from the rhetoric and the ad hominem you wouldn't come across as a bit of a troll.

I don't profess to know squat, I'm merely standing on the shoulders of giants with a willingness to learn and maybe eventually understand some of the physics associated with this fascinating hobby. I'm always ready to be challenged with my understanding, it's one of the ways to learn, it makes me step back and re-evaluate my understanding, the ONLY thing I know for certain is that I've got a lot to learn, so I'm ready and willing to see and read your proof, maybe I can learn something new

 

[W5LZ]

... and imagine my conundrum when impedance is composed of imaginary numbers! But then both that (+/-J), reactance, and (R), radiation resistance, are imaginary numbers, neither are 'real'. Oh well, what's the difference, it's all 'magic' anyway...Right?
- 'Doc

(I may change this post later. I woke up late and just took my meds, and more importantly I have only had one cup of coffee.)

 

[wavrider]

Lack of caffeine will do it every time, especially when I try posting before the first cup.