Remember that when you side mount the antenna, the directivity will depend on
the spacing from the mast/tower. When 1/4 wavelength away, you will get one
node in the direction of the spacing. At 2/4 wavelength there will be 2 nodes
(right and left). For each additional 1/4 wave spacing you will pick up
another node. The further you go out (or the smaller the mast/tower cross
section), the less distinct the nodes will be.-Mike-
From: Keith Dutson <kdutson@sbcglobal.net>
To: towertalk@contesting.com
Sent: Friday, January 9, 2015 1:02 PM
Subject: Re: [TowerTalk] Repeater Feed Line
Jim,
Thanks for all of the great information, especially references to
hard-to-find parts.
Based on a suggestion from another responder, I have decided to use LDF4-50A
for the entire run from entrance panel to antenna. I already have Andrew N
connectors for that run, plus an N Polyphaser at the entrance panel.
As it turns out, placement of the antenna on the side will add directivity,
and this is a plus, as most users are south of my tower. I would rather use
a dB Products four folded dipole antenna, but have not found one for sale.
73, Keith NM5G
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Brown
Sent: Friday, January 09, 2015 1:11 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Repeater Feed Line
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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