[TowerTalk] Cage Vertical

[Peter Forbes]

Hi Peter,

I have been reading the discussion regarding cages - very interesting.

What really interests me is your comment about using a SteppIR as top 
loading.

Currently, I am using a 52 foot free standing tower with a 204BA and 5 el 
18-30mhz log periodic and am shunt feeding the tower with an omega match.

All cables, beams, rotator, switching relays etc. run down the centre of the 
tower and exit at the bottom and into a large box which contains all cable 
terminations etc.  as well as the tuning unit for 160mx.

I am currently replacing all this with a SteppIR antenna on top.    So far, 
I have run shielded control cable for the SteppIR underground  (about 90 
feet) to the terminating box where it is terminated, and intended running 
the shielded cable up the tower centre.

What I am wondering, is did you take any extra precautions other than the 
cable shielding to reduce any chance of RF pickup on the SteppIR motors, 
whilst operating shunt feed on 160mx.?

I know that the rotator control leads pick up a small amount of RF, but not 
sufficient to worry me, but was wondering what effect might occur on the 
SteppIR.  I know that simply adding RF capacitor bypassing might cause 
problems to the steppir motor pulses, as might adding toroids for 
suppression.

I have searched the SteppIR archives, but you are the first I have seen who 
has mentioned shunt feeding.

Power level is a solid 400 watts, so there is quite a deal of RF floating 
around.

I would be nterested in your ideas Peter.


Cheers

Peter   VK3QI


----- Original Message ----- 
From: "Peter Chadwick" <g3rzp at g3rzp.wanadoo.co.uk>
To: "Barrie Smith" <barrie at centric.net>; <towertalk at contesting.com>
Sent: Monday, July 18, 2005 6:59 PM
Subject: Re: [TowerTalk] Cage Vertical


> W7ALW said:
>
> >Since I'm planing to shunt feed a 70' tower before this coming fall, I'd
> be
> very interested in discovering good information on the cage-vertical.<
>
>
> I shunt my feed my 62 foot tower (top loaded with a 4 ele Steppir now) on 
> 80
> and 160 with just such a 'wide conductor'. Three wires in the same plane,
> about 8 inches between them. For spreaders, I use copper water pipe - you
> can run the wire  through holes in the pipe, and put on a binding wire.
> Worth soldering the whole lot up though. Although I have used ordinary tin
> lead solder, it eventually degrades, I find, and so now I use silver 
> solder
> to BS1845 grade AG2, also known as Easyflow No2 in the Johnson Mathey 
> range.
> That's a hard solder of 42% silver, 17% copper,16% zinc and 19% cadmium,
> with a solidus temperature of 610C and a liquidus temperature of 620C. You
> need  special flux for it, but that's fairly easy to get from the same
> source as the solder itself, and of course, a propane or butane gas 
> torch -
> it need to get literally red hot. The flux is a powder which you mix with
> water to a paste, and apply liberally. Of course, the metal needs to be 
> well
> cleaned first. I haven't noticed any corrosion after it's been outside,
> although it's worth dropping some cold water on the joint once it's
> solidified to remove any remaining flux. Note that when silver soldering,
> you MUST not have any tin lead solder in contact with it.
>
> I find it works very well. I have no radials at all - just 4 off 4 foot
> earth rods. The ground is thick wet blue clay from about 6 inches down. I
> tried both ground mounted and elevated radials, and found adding them made
> no measurable difference to the feed point impedance, and in neither case
> could I measure any current in them.
>
> However, I've worked such niceties as VK0 Heard Island on 160 with
> it...........a PY in the middle of summer........3B9C of course.
>
> All this was with the top loading consisting of a 205BA at 62 feet, and an
> interleaced 4 ele for 10 and 4 ele for 15 at 68 feet. The Steppir offers
> less loading, and the resonance point is now within 80metres. This means
> that the impedance at the end of the feed line varies wildly enough that I
> need two variables in the L network tuner rather than just one, so a 
> current
> project is rebuilding the remote tuner to handle this - in between foreign
> business trips, which are causing a major delay in the project.
>
> 73
>
> Peter G3RZP
>