It is commonly called "Drop Wire" and is still available from numerous
places. I once heard that it was 75ohm twinlead but never checked it. I
have used it at numerous locations for dipoles and longwires.
Later,
Kevin C. Kidd, CSRE/AMD
AM Ground Systems Company - WD4RAT
kkidd@kkbc.com -- 866-22-RADIO -- 866-227-2346
www.amgroundsystems.com
On Tue, Mar 25, 2014 at 6:40 PM, Tom Osborne <w7why@frontier.com> wrote:
> Hi Jim
>
> I wonder if we are talking about the same 'twisted pair?'
>
> The wire I was talking about was the old telephone wire they had back in
> the 50's and 60's that came from the pole to the house. I think most of it
> was probably number 12 or so copperweld wire. It had a funny insulation -
> almost like tarred rubber on some of it. 73
>
> Tom W7WHY
>
>
>
>> Perhaps for AWG 16 magnet wire or something.. but for AWG24, it's about
>> 100 ohms (e.g. Cat 5 is specified at 100 +/- 15 ohms)
>>
>> twisted pair is much like any other parallel wire transmission line..
>> Z = 120/sqrt(epsilonr)*acosh(s/d)
>>
>> so to get Z low, you need high epsilon and/or very close spacing.
>> acosh(1) = 0, so there is hope..
>> But acosh(1.1) = 0.433, so air insulation with spacing of 10% of the
>> diameter is 53 ohms.
>>
>>
>> Virtually all of the loss in transmission line
>>
>>> below VHF is due to copper loss, so big copper means low loss, and a
>>> good twist minimizes both radiation and pickup on the feedline from
>>> differential mode current. A good choke is still required to kill common
>>> mode current.
>>>
>>
>>
>>
>> As the Z of the transmission line increases, the dielectric losses
>> increase (because they're tied to voltage) and the ohmic losses decrease
>> (because they're tied to current). Going from 50 to 200 ohm Z increases
>> the dielectric loss by a factor of 4 and decreases the ohmic loss by a
>> factor of 4.
>>
>>
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>>
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