[Elecraft] Twisted Pair Wiring and RFI Rejection

[Jim Brown]

On Mon, 30 Aug 2010 23:08:34 -0800, Edward R. Cole wrote:

>I believe Cat-5e is isolated up to 100-KHz.  

In essence, the ability of twisted pair to reject HF noise is directly 
related to the number of twists per inch, and the uniformity of the 
twist. The close spacing of the twist also helps. High quality twisted 
pair like any of the CAT5/6/7 cables continues to reject noise well into 
the VHF range, although the degree of rejection degrades with increasing 
frequency. Noise rejection is also a function of the balance of the 
receiver, and to some extent, the balance of the output stage that 
drives the line. 

CAT5/6/7 cables as a group are constant impedance (100 ohms) and have 
relatively good bandwidth (well into the tens of MHz). Like any 
transmission line, loss increases with frequency. 

73, Jim K9YC