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@cox.net>
>Subject: Re: [TowerTalk] Insulator Placement - A Releated Thought
>To: "'TowerTalk'" <towertalk@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@contesting.com
>[mailto:towertalk-bounces@contesting.com] On Behalf Of
>donovanf@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@earthlink.net>
>>Subject: [TowerTalk] Insulator Placement Clarification
>>To: TowerTalk <towertalk@contesting.com>
>>
>>Dumb question of the week:
>>What if the antenna is a Log Periodic (10-30 MHz?
>>
>>73, Dick, W1KSZ
>>
>>_______________________________________________
>>
>>
>>
>>_______________________________________________
>>TowerTalk mailing list
>>TowerTalk@contesting.com
>>http://lists.contesting.com/mailman/listinfo/towertalk
>_______________________________________________
>
>
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
>
>_______________________________________________
>
>
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|