krw
att.bizzzzzzzzzz> wrote:>> 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.
Actually, that's why it works so well as a balanced
transmission line.
>>>> 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.
I'd suggest studying transmission lines and antennas.
Start with Kraus.
