Gary,
You're correct that six feet to the first insulator is likely to cause
a resonance in the vicinity of 28 MHz in that set of guys.
However... Frequent energetic guy motion in the wind will damage the
solution you described.
The best approach is to add a new insulator near the tower. Here are
two alternatives to achieve closer spacing:
- install a new insulator with wire clips (e.g., Crosby clips) as
near as possible to the tower. This should get you within perhaps two
feet. But this is lots of work, ugh!
- a better solution is to use an insulator shackle at the top of
each guy. These are over sized shackles commonly used on AM broadcast
and VLF/LF towers to place the first insulator very close to the tower.
Think of it as a large U-bolt shaped shackle, with a curved forged
bolt (instead of a straight bolt) across the the end of the shackle.
The curved bolt passes through the hole in the insulator.
I have some forged insulator shackles in my junk box that I could ship
to you if you want to use that easy solution. These insulator
shackles are 2.5 inches between the legs and 8 inches long (just like a
U-bolt), and made out of 1/2 inch diameter forged steel. Their
strength far exceeds the strength of 1/4 inch EHS. They fit any guy
insulator with diameter of 2.5 inches or less and a hole diameter of
1/2 inch or more. They fit the common "502 johnny ball" insulator
perfectly.
Depending on the design of your tower guy attachment, its likely that you'll
need a smaller 5/16 inch or 3/8 inch standard shackle to attach
the insulator shackle to your tower guy attachment.
73!
Frank
W3LPL
---- Original message ----
>Date: Sat, 10 Feb 2007 08:24:00 -0700
>From: "StellarCAT" <RXDesign@ssvecnet.com>
>Subject: [TowerTalk] Seperation?
>To: "tower" <towertalk@contesting.com>
>
>Steve,
>
>I will be out there helping you with Pauls install - at least
>for a day.... I have my 80 F12 dipole
>(the same one Paul got) separated by 16' from the 20 antenna
>(the one to be worried about
>per Tom) and it works superbly... 6' will probably work fine but
>it is just a quess. I believe Tom
>told me that there are no concerns about how close you space it
>to any 20 antenna - if and only if
>in ALL cases you turn the 80/75 ninety degrees from the 20 no
>matter what spacing - again according
>to Tom.
>
>Also I need to call you soon as I would like you to quote doing
>a change on my tower as well. I went
>with 1/4" EHS with insulators spaced the right distances... I
>believe all works fine with the one
>exception of the attachment to the tower. I have 6' to the first
>insulator BUT I don't think the ARRL
>in publishing their chart for good distances with no interaction
>took into account the fact that it is
>going THROUGH the tower at this point and thus closer to 13.5'
>in length! Anyway I was hoping
>to try to insulate the steel guy from the tower. Using a couple
>or several layers of HD heatshrink or
>something similar. I believe 2 of the 3 guys is all that should
>be needed... and I have 3 guy sets.
>
>regards,
>
>Gary,
>K9RX
>
>Howdy, TowerTalkians --
>
>
>I'm putting a F12 80M dipole above a MonstIR soon. Has anyone
>done this? Did
>you notice any effects - good or bad?
>
> I think we're going to have about 6' of separation and I'm
>wondering if
>that's enough. Tnx.
>
>Cheers,
>Steve K7LXC
>TOWER TECH
>
>
>
>_______________________________________________
>
>
>
>_______________________________________________
>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
|