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Re: [TowerTalk] Repeater Feed Line

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Repeater Feed Line
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Fri, 09 Jan 2015 11:11:00 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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
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