[Elecraft] elecraft,RJ45 Standard

[dave]

 > You're missing the fact that although these conductors INTENTIONALLY
 > carry DC and low rate signals, they also can PICK UP RF and AF noise.
 > Twisted pair, when used to carry a signal, is at least as powerful at
 > rejecting RF and AF noise pickup as coax, but ONLY if the pair is
 > dedicated to a circuit.

And also only if the twisted pair is properly terminated in a balanced 
termination - on both ends. I was field engineer for Bell. I was 
sometimes totally amazed at just how good twisted pair are at 
rejecting noise. As good as coax, if not better.

But . . . the telco pairs are terminated in carefully balanced 
terminations. I don't think the typical ham/audio install is so 
carefully designed. They may be, I don't know for sure. I suspect the 
terminations are, for the most part, unbalanced. There will still be 
some rejection of noise, maybe a good deal. But not as good as if 
properly terminated.

I have used twisted pair here with good success, but there is some 
luck involved if the pairs are not properly terminated.

73 de dave
ab9ca/4



On 5/9/16 12:03 PM, Jim Brown wrote:
> On Mon,5/9/2016 9:41 AM, Lynn W. Taylor, WB6UUT wrote:
>> If we're talking DC levels, sure, no problem.  Low rate signalling
>> just won't matter.
>
> You're missing the fact that although these conductors INTENTIONALLY
> carry DC and low rate signals, they also can PICK UP RF and AF noise.
> Twisted pair, when used to carry a signal, is at least as powerful at
> rejecting RF and AF noise pickup as coax, but ONLY if the pair is
> dedicated to a circuit. That only happens when both ends of the cable
> are correctly wired. That is, OR and OR/WH will reject noise, but OR
> and GN will NOT.
>>
>> At audio levels, the shielding from twisting the wires might be
>> helpful.
>
> It is VERY helpful.
>
>>
>> If we're actually using them for Ethernet, then the twisted pairs
>> aren't wires, they're transmission lines.  100 megabit ethernet is
>> running at 100 megahertz.
>
> Right. AND -- they are transmission lines at RF frequencies even when
> the INTENDED signal is AF or even DC.  THAT'S HOW they reject RF and
> AF noise.
>
>>
>> Wire the cable randomly and you don't have twisted pairs
>> (transmission lines) at VHF frequencies (or above).
>
> And you don't have them at AF or HF either.
>
> Bottom line -- CAT5 and similar cables are excellent for control
> wiring and even for RF, but we must  ALWAYS wire them so that every
> circuit uses a pair. Wiring them any other way is a recipe for noise
> and RFI.
>
> 73, Jim K9YC
>>
>> 73 -- Lynn
>>