[Antennas] spencer dipole from Mccoy's book

[Dan Richardson]

At 02:18 PM 1/3/2002 -0800, you wrote:
>OKnow please tell me the difference between window line and open ladder 
>line.   I have wondered about what the rain would do to the line.  So it 
>makes the line "lossyer"?


Window line which is sometimes also called ladder line looks much like flat 
300 Ohm TV ribbon line. The difference being it is wider -a little less 
than one inch wide - and it is covered with the same type of polyvinyl 
plastic, however it has rectangular holes cut in the center, about one and 
one quarter by five eights inches. There are approximately four holes per 
foot resulting in having a cable having about sixty percent plastic and 
forty percent air dielectric. When dry the line will have a little higher 
loss that open line due to fact that the plastic's dielectric loss is 
higher than that of air. What causes the added losses when wet is the 
dielectric loss of the plastic is increased when wet. Additionally, dust or 
any dirt build up on the line will add additional losses too.

Open line, as the name applies, has nothing but air between the conductors. 
In reality there are spacers but they take up a very small portion of 
space. For example, the open line I am using is made of insolated number 
sixteen wire which has one quarter inch diameter by one inch long nylon 
spaces every foot or so. The results in having ninety eight percent of the 
line with an air dielectric. So only about two percent of this dielectric 
is affected when wet compared to about sixty percent of the window line. 
Plus nylon has a lower dielectric loss than polyvinyl.

I hope this helps.

73
Danny, K6MHE