Towertalkians:
As you know,I raised a question about CATV hardline connectors which
prompted other questions about matching 75 ohm to 50 ohms.I am now
trying to calculate the electrical length I need to cut the 75 ohm CATV so
as to eliminate using 5075 ohm transformers.Both towers will accept up to
250 ft of feedline each.The formula I used to calculate electrical wavelength
is:983.6 divided by freq.X velocity factor.The VF I used was 81%.On one of
my towers I have a 3 ele 40 mtr beam,160 inv L,and a 80 mtr inv L.Using the
formula,I came up with the following:
1/2 wave at 1810 = 220.20 ft
1 wave at 3550 = 224.42 ft
2 waves at 7100 = 224.42
Should I cut this feedline at 224.42 ft to operate all the antennas on this
tower?Will that length work OK at the 1810 frequency with acceptable swr?
My second tower has a KT34XA tribander,80 mtr dipole,40 mtr sloper.
I calculate the following lengths:
1 wave at 3550 = 224.42
2 waves at 7100 = 224.42
4 waves at 14100 = 226.00
6 waves at 21100 = 226.50
8 waves at 28.100 = 226.80
The tribander being the most important of the antennas on this tower,should
I cut the feedline at 226.00 to operate all of the antennas on this tower?Will
that length be close enough to be acceptable with the other antennas also?
Both towers have remote antenna switches where the hardline terminates.
My next question is this:I will be needing to run flexible coax to the antennas
from the remote coax switches.Do I run 50 ohm cable or continue with a 75 ohm.
And,depending on which impedence I am told to use, are these additional lengths
to be considered in my total electrical length calculations?
I am sure by now you have figured out that I have very little knowledge on
real technical electronics,but am willing to do my homework.I hope I dont
sound too stupid.I really appreciate all of your peoples expertise on my
project and look forward to your replies.
Thanks and gud DX, 73 de WT9QBob

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