[TowerTalk] Insulator Placement - A Releated Thought

Tue Sep 4 20:42:38 EDT 2007

Bob is correct about the diode effects potentially caused by guy wire attachments to towers.  Guy tension helps to reduce the probability of a serious problem, but for multi operator and single operator two transmitter stations the RF noise caused by bad joints is a potentially important issue.

The best solutions are:
   non-conductive guys,
   electrically bonding the guy wire to the tower.
   insulator shackles to place the insulator inches from the tower, or
   placement of the first insulator within a few feet of the tower.

The more guy wires you have, the more likely the RFI problem is.  Perhaps the highest RFI risk is on a vertical radiator where the fields are intense at the guy wire-to-tower interface.

73!
Frank
W3LPL

---- Original message ----
>Date: Wed, 5 Sep 2007 00:18:07 -0000
>From: "W3YY" <w3yy at cox.net>  
>Subject: Re: [TowerTalk] Insulator Placement - A Releated Thought  
>To: "'TowerTalk'" <towertalk at contesting.com>
>
>For the record, regarding the original question, I concur with the
>suggestion to use Phillystran or another non-conductive guy.  There are many
>other good reasons to use non-conductive guys (you can tell I'm a convert),
>but I won't go into that.
>
>FWIW, I think another reason for minimizing the length to the first
>insulator, if you are using conductive guys, is to prevent any non-linear
>diode type effects occuring in the guy to tower connection.  The point at
>which a conductive guy meets a tower is not a hard bonded connection, but is
>rather a small surface to surface connection, e.g., typically a thimble or
>wrapped guy cable against a bolt.  It is prone to developing some kind
>corrosion, after which that joint begins to act like a diode and begins
>rectifying AND CREATING HARMONICS when RF currents pass through it.  The
>only answer is to either keep the lengths of conductive elements on either
>side of the diode short or install a bonding strap across the joint.
>
>It was a long time ago, but I worked in the field as a civilian Navy
>engineer and we had tremendous problems with RF noise created by such
>non-linear joints that seemed to be everywhere topside on typical Navy
>ships.  MIL-STD-1310, at the time and perhaps still today, defined the
>bonding and grounding remedies required.  
>
>To be honest, I've never seen a documented evidence of harmonics being
>created in a ham installation due to this effect.  Maybe the typical tension
>on the guys we use is enough to maintain a linear connection.
>
>Anyway, that's some related food for thought.
>
>73, Bob - W3YY
>      
>
>-----Original Message-----
>From: towertalk-bounces at contesting.com
>[mailto:towertalk-bounces at contesting.com] On Behalf Of
>donovanf at starpower.net
>Sent: Tuesday, September 04, 2007 11:45 PM
>To: TowerTalk
>Subject: Re: [TowerTalk] Insulator Placement Clarification
>
>Dick, 
>
>You question is much more complex than it would appear because of the five
>ham bands covered by a log periodic antenna.  There's no simple answer, and
>an EZNEC model would provide the most accurate understanding of the
>tradeoffs.
>
>The simple answer for a 5 band antenna is to use Phillystran or fiberglas
>for at least the top 40 feet of each guy.   Otherwise, use on
>insulator every 8 feet or so for the top 40 feet of each guy.
>
>73!
>Frank
>W3LPL
>  
>
>
>73! 
>Frank
>W3LPL 
>
>---- Original message ----
>>Date: Tue, 04 Sep 2007 19:26:42 -0400
>>From: "Dick, W1KSZ" <w1ksz at earthlink.net>
>>Subject: [TowerTalk]  Insulator Placement Clarification
>>To: TowerTalk <towertalk at contesting.com>
>>
>>Dumb question of the week:
>>What if the antenna is a Log Periodic (10-30 MHz?
>>
>>73, Dick, W1KSZ
>>
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