[TowerTalk] Coax, conduit and toroids

K8RI K8RI-on-TowerTalk at tm.net
Tue Jun 26 17:57:46 PDT 2012

On 6/26/2012 8:30 PM, Rick Kiessig wrote:
> I'm interested in suggestions for how to best segment the coax running
> between my shack and tower-mounted antenna. I'm thinking of something like
> this: (1) from shack to the base of the tower through conduit, tied to
> ground rod via lightning protector, (2) up the tower, (3) from the top of
> the tower to the antenna, tied to #2 using a barrel connector and wrapped
> with weatherproof tape. The runs are fairly short, roughly 20m from the
> shack to the base of the tower and 10m up the tower. Have I missed anything?

Grounding to the tower at the top and bottom is a good idea.

> I'm thinking of using LMR-600 for the first two segments (seems easier to
> handle than Heliax),

It is, but unless you are running QRO and/or UHF it's quite a bit of 

>   and LMR-400UF for #3,

 From personal experience with both LMR 400 and 600 UF the UF versions 
do not stand up well out in the elements.
I use Davis BuryFlex(TM). It's almost as flexible as the UF cables and a 
lot more durable.

>   with UHF-style connectors for

UHF connectors are difficult to find for LMR-600.  Davis was the only 
company I found who would get them for me.  They were a clamp type.
Using UHF connectors and UF cable I'm going to assume you are talking 
about feeding a tribander or something similar.

> each. For my current setup, I ground the coax before it enters the shack.
> The new tower will be right next to the house, so the tower ground and the
> before-entering-the-shack ground will be the same thing.
> What should I do to help ensure that the inside of the conduit stays dry? Is
> applying some sort of weatherproof sealing compound to each end enough?

It's probably impossible to insure it'll stay dry, but a good start   
would be http://www.rogerhalstead.com/ham_files/cablebox.htm
It's how I run the coax from both the shop and house to the tower. Check 
the 3rd and 4th photos from the top and the bottom two rows. This 
presents a good way to terminate the coax out of the weather as well as 
entering the house without damaging concrete.  I really don't worry 
about the conduit staying dry inside unless I have connectors some where 
inside the stuff.  IIRC I included an explanation of what I did as well.

> I'm planning two coax runs and two control cable runs, in two separate
> conduits, coax in one, control in the other. What's a reasonable diameter
> and turning radius for the conduit? The Times Microwave
> specifications/limits are one thing, but I also want to do what I can to
> ease/simplify the process of pulling the coax through the conduit once it
> gets installed.

Use lots of cable pulling soap! Note the last photo in the above link.
I also used two sweep 45s in place of a single 90.
Size wise make the conduit large enough to hold at least twice as much 
as you plan on putting in. That's for ease of pulling and unexpected 
future events.
Also, don't forget to install a pull cable.

> Are there any precautions I should take with regard to running the coax or
> control lines near existing electrical wiring for the house? I'm trying to
> avoid proximity as much as I can, but I'm wondering how far I should go.

I'd keep them at least 3 to 5 feet apart if possible. Farther in very 
dry conditions, but often we have to make do with what we have.  I 
actually have my control wiring and coax in the same conduits.

> Is it a good idea to create a coil of coax in or near the base of the tower,
> run through ferrite toroids? I do this at the base of my vertical, but I'm
> not sure if it's as useful for a horizontal antenna.

I have a one of these current chokes/baluns on each of my sloping 
dipoles. On 75 I still had so much feedback that all the LEDs in the 
shack would light by the time I reached a KW out let alone 1.5 KW. I 
added a second choke in the 75 meter feed line at the tower and it 
cleaned it up to where I can not detect any common mode voltage making 
it back to the shack.  If you need one, use one, if you don't then save 
your money.
>   I am planning to
> continue to use toroids at the shack end of the cable. Should I also run the
> antenna and rotator control cables through toroids at both ends?


Roger (K8RI)

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