[TowerTalk] CATV length

[Richard Thorne]

ROBERT SAUVAN wrote:
> 
> 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 50-75 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 WT9Q--Bob
> 
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Also remember if you use the transformers, remote switches like the
RCS-4 (runs control voltage on coax) will not work.  If your using
switches with the extra control voltage line you'll be ok.


-- 
73,
Rich Thorne - WB5M
Amarillo, TX
rthorne@arn.net

--
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