On 29 May 1998 10:34:51 -0500 "Ted Boerkamp"
<Ted.Boerkamp.0136422@nt.com> writes:
>i am putting up a 48ft self support tower...on top
>will go a TH7 tribander...i wish to run one feedline from
>shack to a RCS-4 antenna relay box...at top i will string wire
>antennas to cover 40,80,160...so will make up jumpers to go
>from RCS-4 up to these antennas...total length of feedline
>from shack (just outside the wall-jumper required to go inside)
>to bottom of relay box is abt 160-170ft.
>i also want to put up an omni directional VHF antenna (for cluster
>connect/bbs etc) on a side arm up abt 45ft. cable run to be abt
>same length as HF run....now the questions....
>1. What cable should i be looking at for both the HF and VHF feedlines
> based on the lengths?? Can i use 75 ohm CATV in both cases?
According to the program TL, here are the losses in 170 ft of
some different types of cable: (best viewed with a fixed font, such
as Courier)
28.5 MHz 146 MHz
3/4 inch CATV .6dB 1.54dB
1/2 inch CATV .77 1.89
9913 1.18 2.7
RG-213 2.03 5.26
Looks to me like 9913 or 1/2 inch CATV would be good choices for
both runs.
>2. If u use 75 ohm cable, will i need transformers of any type to
>match
> the 75 to 50 ohm loads??
Linear transformers for 146 Mhz would be easy, but probably not
really necessary. For HF, if you choose a length that is 3/2
wavelengths on 7.06Mhz (approx 169 ft. Cut to exact length with
an antenna analyzer), you will minimize swr on 40 thru 10. Even
this step is usually not necessary (unless you are using an
Alpha 87, or a solid-state rig with no tuner).
>3. Should the jumpers at both ends of the runs also be 75 ohm
>(assuming
> 75 ohm CATV is used) or can i get away with rg213 jumpers??
RG-213 is fine.
>4. Does anyone have the attenuation specs for 75 ohm CATV for various
> frequencies??
See above, or download the TL program from the ARRL server.
Dave Hachadorian, K6LL
Yuma, AZ
K6LL@juno.com
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