[TowerTalk] LMR600 male DIN - baluns, coax and grounding immediately

Grant Saviers grants2 at pacbell.net
Thu Sep 8 12:16:20 EDT 2016 

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 at 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 at aol.com
>>> Sent: Wednesday, September 7, 2016 8:56 AM
>>> To: john at kk9a.com ; towertalk at 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 at 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 at contesting.com
>>> Subject:    Re: [TowerTalk] LMR600 male  DIN
>>> From:    "Roger (K8RI) on TT" <K8RI-on-TowerTalk at 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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>>>
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>>>
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>>
>
>

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