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TopBand: Re: Tower used on 160m vs. Packet Node

To: <topband@contesting.com>
Subject: TopBand: Re: Tower used on 160m vs. Packet Node
From: n7cl@mmsi.com (Eric Gustafson)
Date: Fri, 14 Nov 1997 17:06:01 -0700

To: <topband@contesting.com>
>Date: Fri, 14 Nov 1997 08:36:13 -0800
>From: Ron Hill K6UR <k6ur@lightspeed.net>
>
>I am thinking of putting up an inverted L antenna using my 89 ft
>tower however I have a packet node with uhf/vhf antennas in constant
>use. Has anyone experienced problems with RF giving problems of 
>getting into uhf/vhf radio's?
>
>I don't want to go ahead with a 160m antenna project only to find that
>I've blown up 5 packet radio's and my node computer. :(
>
>Ron, K6UR
>

Ron,

You should not have any problems (we call 'em "insurmountable
opportunities" around here) with safely driving that system as a
160 merer antenna so long as:

1.  All of the feedlines (and control lines, etc.) associated
    with the tower are properly routed and bonded.  This means:

    a) Feedlines (and other cable shields) bonded to tower at
       business end and again at the point where the line leaves
       the tower.  This is proper lightning damage control
       protocol in any case.  If the tower was much taller you
       might also want to bond the halfway point as well.  But I
       wouldn't bother with that for 89 feet of tower.

    b) Feedlines and control lines routed down the inside of the
       tower structure.  I'm assuming triangular open tower
       construction like Rohn 25, 45, 55, etc.

    c) Feedlines and control lines exit tower as close to the
       base (low to the ground) as possible.  More than a foot or
       two up is too high.

    e) No unshielded control lines

2.  The ground at the base of the tower is good enough to support
    the vast majority of the 160 meter antenna current.

3.  (Possibly not necessary if condition (2) is well met) All the
    lines mentoned in (1) above decoupled so that the impedance
    (at 1.8 MHz) looking from the tower along these lines to the
    equipment is much higher than the impedance looking from the
    tower into the ground connection.

4.  (Also possibly not necessary but you might want to consider
    depending on how much 1.8 MHz RF power you intend to
    generate)  RF bypass capacitors from individual control wires
    to shield at both ends of cable.  And VHF RF feedlines
    connected to radio equipment through highpass filter(s)

"Feedlines" includes the 160 meter feedline where appropriate.

Hope this is useful.

73,  Eric  N7CL

-- 
------------------------------------------------------
Eric Gustafson  N7CL      | The mountains are high and
6730 S. Old Spanish Trail | the Emperor is far away.
Tucson, AZ 85747-9498     |
                          | You can't work 'em
INTERNET: n7cl@mmsi.com   | if you can't hear 'em.
------------------------------------------------------

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