Re: [IRCA] Cable connectors

[Rick Kunath <k9ao@xxxxxxxxxxx>]

Extremely interesting...

<Snipped> Here and there

> Another part of the test was to wind a dozen turns through a large ferrite
> toroid.  No difference at all.  Also tried a new "un-un" to do a ground
> isolation.  Again, no change.

I'm wondering about the core material for that test toroid? You'd likely need 
a stack of cores to get the series impedance that you need to reduce the 
ingress. More turns is good up to a point, then the distributed capacity gets 
you, but that affects the upper end of the range first. You can reduce that 
effect by winding the turns through the core in large loops, and splaying them 
out spaced equally around the core. That will reduce capacity effects. I'm 
guessing that you didn't have enough impedance with that particular choke.

> I might agree with that except CAT5 is designed to limit the interaction.
> The individual pairs are tightly twisted, but not identical turns per foot
> for each of them.  What that does is cancel the interaction.

It does not cancel the interaction, it tends to make the interaction 
symmetrical on a given pair. And that helps balance for that one pair.

The fields still extend outside the physical space of the twisted wiring. The 
isolation can be anywhere from -40 to -80 dB  between pairs and maybe a bit 
better. That's based on resistive termination at the characteristic impedance 
of approximately 100 ohms.

> If they weren't twisted, that may well be true.  I also have to think that
> the loss of the cable on the ground would more greatly reduce the ingress
> than increase it.  While I didn't add this to the article, I did run a
> further test.  I laid out a 50' length and terminated it with a 100 ohm
> resistor.  That made the whole thing balanced when the receive end balun
> was included.  After taking a set of bandwidth readings, I laid a 50'
> length of chicken wire on top of the cable.  The goal was to provide some
> shielding via capacitance to the ground.  End result was no change at all.

On that test, how much ingress was there? Anything? 

> One of the more important things I've learned in my lifetime is to leave my
> ego outside.  If someone has an improvement, I'll grab that in a heartbeat.

Yep, me too. Ideas tend to breed better ones and better understanding. 
Anything that helps and I'm in. 

As I always say, theory is one thing, but sometimes things don't always go as 
you would theorize. Sometimes, through experimenting and the shared work of 
others, you realize that you didn't have exactly what you thought you did. And 
while the theory always works, you have to apply the right one to the 
situation at hand :)

Rick Kunath

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