JosephKK
yahoo.com> wrote:>On Thu, 06 Mar 2008 15:40:31 -0900, floyd@
apaflo.com (Floyd L.
>Davidson) wrote:
>
>>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.
>
>I have built many twin lead antennas for VHF use. The distinction is
>not so clear as you are advertising.
In fact, it is. What is an folded dipole? As opposed to a loop?
