> krw
att.bizzzzzzzzzz> wrote:>>> krw
att.bizzzzzzzzzz> wrote:>>>>> Foxtrot wrote:
>>>>>>
>>>>> ... snip ...
>>>>>>
>>>>>> Is there is a greaterlikelihood of hum if I connect a "2 wire"
>>>>>> phone extension by using one wire from a twisted pair and taking
>>>>>> the second wire from a different twisted pair?
>>>>>
>>>>> Yes. The idea of twisted pairs is that an interference appears on
>>>>> both lines, and thus tends to cancel itself. Separating the lines
>>>>> makes it easy for unequal induction.
>>>>
>>>>Twisting also makes the loop area low (average over a long stretch
>>>>is nil). Separating them makes a large loop, increasing the size of
>>>>the antenna.
>>>
>>> That is not a valid analysis. It is a transmission
>>> line, not an antenna.
>>
>>It sure as hell is. Open up the loop and it makes a *wonderful*
>>antenna.
>
> It's a "wonderful" antenna regardless. But it's a
> single conductor long wire antenna. Changing the
> spacing is merely changing the effective diameter of the
> single conductor. To get any other effect requires
> spacing that is significant in terms of wavelength
> (greater than perhaps 1/8th of a wavelength, for
> example).
Absolute nonsense.
>>> Consider that the effect, both for relatively small
>>> gauge cables, such as the ubiquitous 26 gauge used
>>> today, is *exactly* the same as the effect on the open
>>> wire lines used in the 30's and 40's with several inches
>>> of separate between a pair of much larger copperclad
>>> steel wires. And while the twist on some cable is
>>> measured per inch, on typical telephone cable it is
>>> measured in many inches per twist, and on those old open
>>> wire lines it was in hundreds of yards per twist.
>>
>>...and open-wire transmission lines won't pick up stray noise?
>
> It picks up as much, or as little, as unshielded twisted
> pair of smaller gauge and closer spacing. That's the
> point... there isn't any difference. In either case
> what you have is a single conductor longwire antenna, not
> a loop antenna, until the spacing is a significant fraction
> of a wavelength.
Bullsnit. Try reading your EE100 text again.
--
Keith
