True 75ohm RCA Type Plug Possible?

It's possible to increase the impedance of an RCA by not using a 100% shield around the center pin, reducing the shunt capacitance. It looks like WBT did this on their plug - there's only three shield contacts, and it looks like the space between them is greater than the width of the contacts themselves.

But the moment you plug this thing into a jack... goodbye 75 ohms. Unless of course there's a matching RCA jack, in which case your equipment has become so specialized that you should have been using BNC anyway.
 
It is absolutely possible. Sorry, carlos..

Nextgen did it by decreasing the shield.

This asymmetry in the shield currents increases the net inductance at the connector by preventing the coaxial cancellation of the magnetic fields outside the shield cylinder. In addition, by reducing the shield total in this fashion, decreases the net capacitance at the connector.

Since Z = sqr(L/C)....increasing L increases impedance, and decreasing C also increases impedance.

They have line males and chassis females which have the same feature, as they spiralled the shield pair in one direction for the males, and the other direction for the females. By using this design, they maintain physical compatibility with all existing rca jacks and plugs, but will remain true 75 ohm only if nextgen wbt's are used together..

Their spiral shield contact solution is useable up to frequencies which have slew features about 1 to 10 times the connector length, that being about 1/5 inch to 5 inches. Above those frequencies, the design they embrace will begin to show lumped element mismatches.

There is a more elegant solution which affords far higher bandwidth impedance match. But to introduce it would undermine all the wbt product, obsoleting it entirely. And, it costs far too little to be a niche product, better as an OEM one..

Cheers, John

PS...sorry, I can't find the magnetic field analysis jpeg I ran which shows how the fields are arranged..guess it's at home...
 
commstech said:
lets say the jacks and plugs are actually structured as 75ohms...will the copper tracks thereafter the jacks need to be specially treated to maintain this impedance throughout the equipment>?

Yes, in fact it is actually more important than the jack itself.

The reflection of signal back is a function of the length of the discontinuity, the longer the discontinuity (incorrect impedance), the lower the frequency that will be affected.

John
 
Nope, sorry. You are incorrect.

Show me, via equations, why it is not so.

Then, I will take those equations, and provide the derivation which indeed, shows that it is possible..

And, I will not need to resort to a word indicative of the effort required for reproduction.

Cheers, John

BTW, in looking at that canare part, I don't think they did..
 
Jocko Homo said:
No, it is not ****ing possible.

Jocko

That 75-Ohm RCA plug is a Canard!
:clown:
 

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Re: It is absolutely possible. Sorry, carlos..

sorry for the noob question, by why is 75 ohm impedence a good thing?


jneutron said:


There is a more elegant solution which affords far higher bandwidth impedance match. But to introduce it would undermine all the wbt product, obsoleting it entirely. And, it costs far too little to be a niche product, better as an OEM one..

Cheers, John


what is this solution you speak of?
 
Re: Re: It is absolutely possible. Sorry, carlos..

homer09 said:
sorry for the noob question, by why is 75 ohm impedence a good thing?


It's a rf reflection thing.. When a signal travels down a transmission line, if it meets a discontinuity of impedance, some of the signal will reflect back towards the transmitter. For long lines, this can cause signal degradation.

75, of course, is just a standard..I did know why it was selected, but have forgotten what it was..I think it was the line impedance necessary for a 1/4 wave transformer between a 300 ohm line and a 50 ohm line, but I'm not quite sure about that.

homer09 said:
what is this solution you speak of?
I am not at liberty to divulge that yet.

However, the solution which was created by WBT, I can most certainly detail at length..

Cheers, John
 
jneutron said:
Show me, via equations, why it is not so.
Then, I will take those equations, and provide the derivation which indeed, shows that it is possible..

Aaaahhhh, that's a good one.:clown:

Let's think, shall we?
Look at an F plug. It's 75 ohms, the center pin is from the cable.
Now look at the center pin of an RCA plug. Much thicker, isn't it?
So, the ground should be much more far apart than on a standard RCA.
Why on earth would impedance change (so much) just by cutting the ground contact in 3 parts?
And the internal connection of the plug to the wire?