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## [TowerTalk] CATV length

 To: [TowerTalk] CATV length rthorne@arn.net (Richard Thorne) Sat, 05 Jul 1997 08:40:19 -0700
 ```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 > > -- > FAQ on WWW: http://www.contesting.com/towertalkfaq.html > Submissions: towertalk@contesting.com > Administrative requests: towertalk-REQUEST@contesting.com > Problems: owner-towertalk@contesting.com > Search: http://www.contesting.com/km9p/search.htm 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 -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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