[Elecraft] RE: zip cord as antenna wire

Thu Mar 25 11:44:00 2004

Joe:
   Your best bet would be to use any open wire feed: 300 ohm, 450 ohm, 
or homemade stuff, spaced 4", that is about 600 ohm.  Your next best 
bet would be to use 450 ohm ladder line (the stuff that is fully 
encased, but has a series of holes or windows between the wires).  None 
of these lines will provide a good impedance match at the join with the 
antenna, except on problematic frequencies.  But this doesn't matter 
much at all, since the line losses of such feeds are small.  (True open 
wire feed has less loss than encased "ladder line", which, in turn, has 
less loss than the good ol' 300 ohm TV twin lead).  However, in any 
case, you want to bring the line into a good balanced tuner, a 
transmatch that can convert whatever wild impedance you have at the 
beginning of your feed line (the feed end, opposite the antenna end) to 
the 50 ohms that the coax from your xceiver wants to see.  Good 
balanced tuners are hard to find, but they are not difficult to build.  
B&W coil stock is still available, as are a variety of variable caps 
from such places as Mouser (new) or Antique Electronics (possibly 
used).  For qrp, or even up to 150 watts, receiver type caps work just 
fine.  A number of designs work very well.  Balanced tuners are 
significantly superior in performance and loss to using baluns, which 
are best avoided.  I call my homemade tuner my "Italian Antenna Tuner" 
because it looks like a plate of spaghetti -- but it sure works, and it 
is very flexible.  I can use it to match my 142' cf zepp from 160-10.

best wishes,

dave belsley, w1euy

On Mar 25, 2004, at 10:24 AM, Joe - aa4nn wrote:

> If zip cord or speaker wire is bad for a transmission line, what if I 
> use
> 300 ohm tv lead as the transmission line to a 44 foot center fed 
> dipole?  Is
> 300 ohm any better ?
> de Joe, aa4nn
>
>> I had known that this means that zip cord makes bad transmission line.
>> Does it also imply that it makes bad antenna wire?  That is, does an
>> unzipped cord, single wire, radiate much worse than wires with other
>> kinds of insulation, when used in a tuned dipole?
>
>
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