[Ccarc] lightning damage to small fiberglass antennas.

Dave & Rita k9dvl at comcast.net
Wed Jun 27 09:58:27 EDT 2007 

Find out what it will cost to weld a new mount on the water tank and a 
moose type ant. cut to 147 mhz. and when we got the money saved up we 
can do it!!

Phil Snider wrote:
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> Subject:
> [LP/PQ] Digest Number 913
> From:
> LightningProtection at yahoogroups.com
> Date:
> 27 Jun 2007 08:27:39 -0000
> To:
> LightningProtection at yahoogroups.com
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> To:
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>   Messages In This Digest (1 Message)
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> 1.
>     antenna damage from streamers <#1> From: Art Snapper 
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>         antenna damage from streamers
>         <http://groups.yahoo.com/group/LightningProtection/message/1876;_ylc=X3oDMTJwbXN1ZHB2BF9TAzk3MzU5NzE1BGdycElkAzE2NzUwOQRncnBzcElkAzE3MDUwODMyOTEEbXNnSWQDMTg3NgRzZWMDZG1zZwRzbGsDdm1zZwRzdGltZQMxMTgyOTMyODU5>
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>           Posted by: "Art Snapper" art at nk8x.net
>           <mailto:art at nk8x.net?Subject=%20Re%3Aantenna%20damage%20from%20streamers>
>             a_snapper <http://profiles.yahoo.com/a_snapper>
>
>
>             Tue Jun 26, 2007 10:11 am (PST)
>
>     I periodically replace small fiberglass radio antennas that appear
>     to have
>     been damaged by positive streamers (upstroke) associated with nearby
>     lightning strikes. The antennas are approximately 3 feet in
>     length, and
>     installed slightly above single story metal warehouses.
>
>     Does the upstroke radiate from the antenna because of its shape,
>     or is it
>     because it is poorly grounded and reaches a higher potential
>     (during the
>     strike) than the building it is installed on? Or are there other
>     factors
>     involved?
>
>     Often the customer installs their own antenna, therefore I am
>     trying to
>     create some guidelines to reduce the issue in the future.
>
>     I could probably solve the problem by providing a more robust
>     antenna, but I
>     am not certain that is the best course of action.
>
>     Art Snapper
>     State Systems Radio
>
>     ---------------------
>
>     Co-moderator's Comments:
>
>     According to Berger (1967, 1968, 1977), a lightning strike to
>     ground can produce secondary upward streamers from pointed ground
>     objects within a relatively large distance. Of course, the
>     intensity of the streamers and the radius from the strike point
>     within which they occur will increase with increase in magnitude
>     of the downward stroke.
>
>     Upward streamers can occur on "short" objects. For example, Berger
>     (1967, 1968) observed such discharges on the steeple of a small
>     church which was only about 10 m high. However, the intensity of
>     the streamers increases with altitude of the peak of the object.
>     For example, the above church was located on a hill about 250 m
>     above Lake Lugano.
>
>     The damage from secondary upward streamers will be limited unless
>     they are intense enough to reach into the clouds and draw
>     subsequent downward strokes. Based on available field
>     observations, Mousa (1986) estimated that subsequent stroke only
>     occur when altitude of the peak of the ground object is about 300
>     m (1000 ft) or larger.
>
>     Regarding the fiberglass antennas in question, the damage
>     apparently results from being a pointed object, i.e. their shape.
>     Quality of the grounding should have minimal effect, if any, on
>     the observed damage. The best solution appears to be to use more
>     robust antennas, especially at locations where altitude of the
>     site is high.
>
>     Thank you.
>
>     References:
>
>     [1] Berger, K. (June 1967). "Novel Observations on Lightning
>     Discharges: Results of Research on Mount San Salvatore", Journal
>     of the Franklin Institute, Vol. 283, No. 6, pp. 478-525.
>
>     [2] Berger, K. (1968). Discussion of Group 33 on "Lightning and
>     Surges", CIGRE Proceedings, Vol. II, pp. 2, 10-11.
>
>     [3] Berger, K. (1977). "The Earth Flash", Chapter 5 of Golde, R.H.
>     (Editor), Lightning, Vol. 1, Academic Press, London.
>
>     [4] Mousa, A.M. (1968). A Study of the Engineering Model of
>     Lightning Strokes and its Application to Unshielded Transmission
>     Lines", Ph.D. Thesis, University of British Columbia, Vancouver,
>     BC, Canada.
>
>     Abdul M. Mousa, Ph.D., P. Eng., Fellow IEEE
>     abdul_mousa at hotmail.com <mailto:abdul_mousa%40hotmail.com>
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