[TowerTalk] from towers to shack

[Roger (K8RI) on TT]

On 12/9/2013 8:29 AM, Jorge Diez - CX6VM wrote:
> Thanks to all for the answers, interesting feedback!, thanks!
>
> Seems I will do it as actually, underground.
>
> Cables will not be direct buried, will go through a plastic pipe, so I don´t
> think that would have considerably more capacitance to ground.
>
> Actually I´m afraid I will find some water or humidity inside the pipe and
> along the cables. Will need to improve that, with a deeper channel, drainage
> and a gentle slope to allow water does not stay inside the pipe.
'
It gets rained on outside.  Avoid connections in the conduit. If you 
can't avoid then, just thoroughly waterproof them.  I don't even have 
drains in my conduit. and it's going on 10 years.  The only concern I 
have about water in the conduit is freezing this time of year.  What's 
there is there to stay, and I doubt I could add more. OTOH, all I need 
to do is set up a heat gun (on low) or hair dryer (on high)blowing into 
the conduit from the basement and let run for a few hours to dry it 
out.  All you need is high volume, "warm" air.  You may get a lot of 
condensation at the tower end.

73

Roger (K8RI)


>
> Lighting is something to improve. A project for next year, very expensive
> since I have more than 18 cables (coaxial and control lines) going to the
> shack. It´s obvious that will need a Polyphaser sponsorship at CW5W :-)
>
> Thanks!
>
> Jorge
> CX6VM/CW5W
>
> -----Mensaje original-----
> De: TowerTalk [mailto:towertalk-bounces at contesting.com] En nombre de David
> Robbins
> Enviado el: lunes, 09 de diciembre de 2013 10:58 a.m.
> Para: towertalk at contesting.com
> Asunto: Re: [TowerTalk] from towers to shack
>
>
>>> Consider a direct strike to the tower? The cables being above or
>>> below ground don't materially change the voltage waveform, at least
>>> as selection of the suppression devices are concerned: it's kilovolts
>>> you need to deal with.
>> Cables "tapped" to the tower are coming off a voltage gradient from
>> several
> hundred KV at the top of the tower
>> to zero at ground (if the tower is properly grounded).  At 10 feet on a
>> 100
> foot tower, one had several 10s of KV ..
>> not easily dealt with using simple devices.
> But of course ground is not 'zero' once the current traveling down the tower
> gets to it, the ground potential rises also.  What you need to protect
> against are the signal/power carrying conductors having a different
> potential than the shields of the coax or ground where the equipment is.
>
>>> Conventional transient suppression techniques work for phone and
>>> power lines, which run above ground for miles.
>> Phone and power lines are not connected to lightning rods several times
>> the
> height of the lines.
>
> Most distribution lines are at the TOP of the poles and get hit directly,
> phone lines are usually 3/4's of the way or more up the poles... and even
> more important they are not coaxial lines so the power carrying conductor is
> hit which takes it directly into transformers, switches, and other
> equipment.
> Important Note, it is not the voltage handling capability of arresters that
> matter, when the arrester turns on from a stroke it limits the voltage
> across itself, that is what its purpose is!  It is the current or integrated
> energy handling capability of the arresting device that is important.  How
> you can help it is by keeping all the grounds bonded together, this keeps
> the potential difference between the protected cable and the local ground
> smaller which reduces the amount of current that the arrester must pass to
> equalize the potential between the signal/power lead and ground.
>
> David Robbins K1TTT
> e-mail: mailto:k1ttt at arrl.net
> web: http://wiki.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://k1ttt.net
>
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