[TowerTalk] Repeater Feed Line

[Jim Brown]

On Fri,1/9/2015 9:00 AM, Keith Dutson wrote:
> I am planning to put up an antenna on my 150 foot Rohn 45 tower for a 2
> meter repeater.  I have plenty of ½ inch Heliax, but a friend said 7/8 would
> be better, and he has a piece to give me.

You didn't say how long the cable run is. The difference is purely a 
matter of loss, and matters most on RX. Loss data for 1/2-in and 7/8-in 
hard line is easy to find. Google for LDF-4 and LDF-5  data sheets.  
Loss data is also included in N6BV's TLW program, that comes with the 
ARRL Antenna Book. Here are some numbers from TLW. LMR-400, pretty good 
213-size coax, is 1.56 dB/100 ft on 2M; 1/2-in is 1.04 dB/100 ft, 7/8-in 
is 0.46 dB/100 ft.

> He said to put the antenna so that the top of the antenna is below top of the tower, to avoid lightning strikes striking it.

That may or may not be good advice.  In any event, the tower will act as 
a reflector, giving the antenna some directivity. Think about the 
resulting pattern when you decide which side to mount it on.

> I cannot accommodate 7/8 hard line from the antenna to the shack, so am
> planning to run it from near the antenna to near the bottom of the tower.,
> and run jumpers to both the antenna and shack.  I am thinking 213 for
> jumpers.

213-size coax has a lot more loss than 1/2-in or 7/8-in hard line. 
Again, it mostly matters on RX.

>   Also, I am thinking the 7/8 needs to be grounded to the tower at
> both ends.

Feedline on a tower should ALWAYS be bonded to the tower both top and 
bottom for lightning protection.

> I am looking for suggestions/recommendations, and where to find connectors
> and grounding hardware.

Hard line connectors must mechanically fit the particular type of hard 
line that you have. Google the part number to find what connectors are 
designed to fit it. Here are some notes that I made myself when I was 
putting together the feedlines for my HF antennas. They are installed 
using a hacksaw to cut the line, wrenches to mount the connector. and an 
iron to solder the center conductor. Again, google to find instructions, 
which are unique to each connector.

Cablewave FLC78-50-series connectors fit LDF5-50A and will work with 
DBC078F5P. They are
very nice connectors.

  Davis RF carries RFS Cellflex UHF Male and Female connectors for 
LDF4-50A. RF Industries also
makes UHF Male and Female connectors for LDF4-50A.

Surplus Sales of Nebraska sells only surplus/discontinued connectors.

The RF Connection and RF Parts sell both surplus/discontinued connectors 
and new connectors for
current products.

Davis RF and The Antenna Farm sell new connectors for current products.

Always check auction sites for hard to find connectors.

The center conductor of Andrew VXL5-50 has a pronounced interior ridged 
thread.

If you buy used connectors, they often come attached to cable, having 
been cut off with a hacksaw. Study the mounting as you take it apart.

73, Jim K9YC