[time-nuts] Aerial coax downlead placement

[W7SLS]

Hi Peter,

>> you should
> 
> never drop the coax down the middle of your support-pole, as the conducting
> pole will mess up the characteristics of the cable by affecting the
> currents in the outer braid.

Well, that is true for ’twin-lead’ (“TV antenna wire”), but is not an issue for coax.
(You _don’t_ want signals on the outside of the coax anyway :)

Depending on what meets your budget for time, $, esthetics, and specifics of that installation,
one or more of these might help:

	- attach the coax to the mast with tie-wraps (loosely, so as not to ‘pinch’ the coax)

	- as above, use “20 cm” of “14 AWG” insulated solid conductor instead of zip ties

	- electric tape is tempting, but will degrade (UV), and can cause the mast to rust 

	- other ideas from group

Also, depending on how much lightning / storms you get locally, add suitable lightning arresting equipment

Good luck,

Scott
W7SLS



> On Jul 4, 2019, at 1:43 PM, Peter Vince <petervince1952 at gmail.com> wrote:
> 
> Hello all,
> 
>     A new contact, whose background is in computer programming rather than
> RF, is getting into accurate GPS positioning, and has been tapping me for
> any knowledge I might have.  I persuaded him to get the new Ublox F9P
> receiver and also a "proper" dual-band antenna - albeit from China, so
> affordable!  This seems to be going quite well, and he sent a photo today.
> He has mounted said aerial on what looks like a six-foot pole which is
> good, but currently the coax down-lead is just hanging - flopping about in
> the breeze.  Now that is bad for so many reasons :-)  However, I am not
> sure of the best advice to give him.  I'm sure I heard that you should
> never drop the coax down the middle of your support-pole, as the conducting
> pole will mess up the characteristics of the cable by affecting the
> currents in the outer braid.  And so similarly, you presumably don't really
> want to tie-wrap it tightly to the outside of the pole for pretty much the
> same reason.  So my gut instinct would be to put some (half-inch??)
> insulating spacers between the coax and the pole where the tie-wraps go.
> Now when I worked in a TV shop in my youth, they didn't bother with any of
> that - a) they probably didn't know about any such effects, b) they
> certainly couldn't have been bothered, and c) TV signals are strong, so it
> wouldn't have made a significant difference.  GPS signals, however, are NOT
> strong, and need to be treated with much more respect - especially if you
> are after some seriously good positional accuracy.  Is my idea right, or am
> I barking up completely the wrong tree?
> 
>     Thanks in advance,
> 
>          Peter  (London, England)
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