Another advantage of hardline is the ease of bonding the shield at the
top and bottom of the tower, which is the correct practice for lightning
protection. Since the shield itself is watertight, the Andrew kits have
a copper strap or clip, depending on the design generation, to go around
the bare shield and a pigtail with a 2 hole lug (code required) for
connection to the top and bottom bonding plates. The kits include 3/4"&
2" vinyl tape, the self sealing tape and instructions for a watertight seal.
For braided coax, about the only choice is a thru panel F-F or inline
F-F with a ground screw and then a wire to the tower ground point top
and bottom. In my experience it is hard to get a good seal of PL to SO
joints.
Re the question: Can I ground the shield for various antenna feed
systems? In theory every antenna is balanced so there is no current on
the outside of the shield, so grounding the shield exterior anywhere is
OK. In practice, we insure no shield current with a hi-Z choke as close
as possible to the feedpoint. If there is an induced current on the
cable exterior from the antenna RF field, such as on the rotator
pigtail, we don't want that so top of tower bonding helps. I think
there is also some benefit for all cable runs to be inside the tower as
it is a reasonable Faraday cage at HF. Easy to do for guyed tower, very
difficult for crank ups. Expecting to ground thru rotator bearings isn't
a ground and will likely cause bearing damage (even from rain static),
so bond coax at the tower top, not on the boom. A separate ground wire
around the rotator, mast to tower top ground point is a very good idea.
As you note, Andrew recommends intermediate shield bonding for tall
towers since the inductance of the coax and tower are different. I used
the commercial leg clips and multi cable rubber grommets for support of
the hardline inside the tower and did not intermediate bond for my 142'
tower.
Good practice (and I think code) has the grounding outside of the
entrance to a structure, tied to a ring around the structure or bonded
directly to the tower which has a surround ring to the rod and radial
field. A tower mounted watertight box with an internal grounding plate
is what I have for crank-up towers with RG feeders. Lightning arresters
are mounted on that plate for each coax and control cable run, and
provide the F-F coax connectors and tower bottom shield bonding in a dry
location. I wish I had installed boxes larger than 14 x 16 x 8.
Grant KZ1W
On 9/8/2016 7:51 AM, StellarCAT wrote:
and more than likely ANYTHING you had done to waterproof the
connectors including water proof connectors would have failed with a
direct hit. Just because a connector might be water proof doesn't make
them a magic energy sink capable of thousands of joules... Grounding
the shell at the top and bottom (and middle if over ~75') which is
what I plan on doing is probably the best thing - and I'm sure you had
that as well.
Indeed therein lies a problem - how to do this AND seal it ... at the
base I'll have a box on the tower so that connection is inside (metal
box with a separate connection from the inside to the tower as well).
All of the antennas but one are hairpin matches so it will be DC
grounded through that at the antenna and the 2 switch boxes (stacking
and then antenna select) will accomplish two more grounding points ...
the 4 element Optibeam 40 will need a think through.... and the rotary
80/75 dipole at the top - its hairpin is a coil and is not grounded
... hmmmm....
that brings up a question: Does having a balun at the antenna - assume
a good one - allow one to ground the shield of the coax to the tower
immediately ... i.e. say the DE is out 20' ... there is a balun there
... can one have another connection at the tower and have that
connection shell grounded - does the balun make this possible? I
believe I know the answer (and I'm trying not to get in to the QUALITY
and capability of the balun) ... but would like to hear from the
experts - K9YC?
Gary
K9RX
-----Original Message----- From: Roger (K8RI) on TT
Sent: Wednesday, September 7, 2016 8:24 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] LMR600 male DIN
I've said it many times, I used to feel like you toward connectors,
until a direct lightning strike to the top of my tower removed all of
the weatherproofing and 15 minutes later I had water running out of my
rig onto the desk top. It didn't hurt the rig, but it ruined the desk
top. 40 years total at 3 locations with nary a problem, but one strike
ruined 200 feet of 9913, IIRC 8 connectors, and a desk top
If you are on HF, Unless it is a long line, or you consider the legal
limit as QRP, as far as I can see, there is little to be gained from
using these expensive cables
I found 1/2" Heliax too fragile for kinking, or being stepped on. I gave
away two 100' runs with connectors. and went to LMR600. Now if I could
have found 7/8ths Heliax at a reasonable price, I would have used it for
VHF and UHF. The only time I saw a good price was a pick up load for
the repeater that was free free, but none as an individual.
Total length from my rigs to the top of the tower was 200 feet with
rotator loops and 28' pigtails to the antennas
73
Roger (K8RI)
On 9/7/2016 Wednesday 7:50 PM, Kevin wrote:
I believe it all started with the superiority of heliax/hard-line
from a loss perspective and since UHF type connectors for such cable
are expensive and rare why not use 7/16 DIN, a commercial standard
connector.
On 9/7/2016 10:26 AM, StellarCAT wrote:
Forgive me - I've replied to Gerald's email but this is directed to
the thread in general: WHY all the concern for sealed connectors and
connector types? I've been using UHF for 49 years and the only time
I've had issues with those installed outside it was my fault -
either poor wrap of tape or poor solder job ... I've had cables with
connectors that were out for years with electrical tape wrapped
around them in 2 directions - years later when disassembling them
for a move they were utterly pristine! I don't get it - why so much
discussion?
Gary
K9RX
-----Original Message----- From: TexasRF@aol.com
Sent: Wednesday, September 7, 2016 8:56 AM
To: john@kk9a.com ; towertalk@contesting.com
Subject: Re: [TowerTalk] LMR600 male DIN
John, you bring up a valid concern. I am not aware of any coaxial type
connector that could be considered waterproof. The fundamental
reason is
because the threaded connections do not create a hermetic seal when
they are
screwed together.
There are inevitable air spaces inside the connectors and coaxial
cables.
These air spaces will fill with air. When the air is heated (like
outside
in full sun) it will expand, creating a positive pressure.
Conversely, when
the air cools (like at night), it will create a negative pressure. This
negative pressure will suck tiny amounts of water vapor through the
threads of
the connector.
If enough water vapor is present droplets of water can condense
during the
cooling cycle and over the course of days and weeks can collect
inside the
connector. Once inside, there is no escape and the droplets continue to
collect over time.
If there are rain or dew drops of water on the outside of the cable,
they
can also leak through the threads and collect inside the connector.
Gravity
is not your friend here.
Many commercial applications pressurize all of the cables even if
they are
foam filled types to prevent the problem. You may have noticed many
of the
Heliax type connectors have air fittings; that is why.
73,
Gerald K5GW
Over
In a message dated 9/7/2016 5:37:52 A.M. Central Daylight Time,
john@kk9a.com writes:
Is any TX connector really water proof? Are DIN's being
professionally
installed with no external butyl rubber and tape? On the two outdoor
DINs
that I have, I weather proofed the connection the same way I did
with UHF
and N connectors.
John KK9A
To: towertalk@contesting.com
Subject: Re: [TowerTalk] LMR600 male DIN
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Wed, 7 Sep 2016 01:08:48 -0400
Take care!
According to the Amphenol page N-Type are not water proof/weather
proof.
73
Roger (K8RI)
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