[TowerTalk] FW: supporting a 40 meter rotatable dipole with trusses

[terry burge]

Thank You Matt,

Your suggestion has sounded the most useful to me. I will say I do hate dealing with Copperweld and have avoided it but we will see. I do have the stuff from the 160 meter coil to turn a hytower into a inv-L which is copperweld. Talk about HARD to cut! More likely I will try to use some kind of wire rope.

I still think the Dacron would work even if I need to go to larger stuff like I used for guy wires on my crankup Rohn 45/25 tower in the past. Stretching could be an issue there. More likely I would double up on the 3/16" Dacron. 

I visualize something like 'H's for a linear loading arrangement but just how much I can only guess. That in combination with a Capacitance Hat/cross piece out beyond the linear loading I think. 

Why am I not trying to do a Moxon? Because whatever I come up with it must be pulled up above my existing Steppir 3 element, then tuned up by tilting vertical to get to the adjustment slip joints. I can't see how that could be done with anything with much of a boom (like a Moxan or 2 element 'shorty-forty). If I could figure that out I would try to put a Waller-Flag above my Steppir. By the way, my steppir has about 30' of boom length and truss.

For the moment I am contemplating how to double up the thicknet of the 1.25" with adding a 1.50" thick wall 0.120" slipped over it. Sounds like I've got some grinding of rivets to do. Is making me wonder about just buying a Cushcraft 40 meter monobander or maybe check out M2 if I think I might break down and spend some cash. JK while I love the look on line at least I think would be too much money. Always looking for something on the used market of course. But then there is the problem that I can't hardly get any large delivery truck into my QTH.

Anyway, I will keep working on this and see what I can come up with. Don't know is the rotatable dipole at about 124' will be an improvement over my 4-Square ground mounted but want to see. Couple of mornings ago around 4:00AM I was having a ball working JA's on 40 meters with great signals both ways. Got reports like 59+20, etc. The 4-Square was really showing it's stuff that morning. Had to check all for directions to make sure I wasn't going to cause any grief to someone when operating.


Thanks to Matt and everyone for the suggestions. Please don't think I'm ignoring or not reading them. Sometimes I just 'don't know what to say' to some of the comments. I'm still learning what many of you have already forgot (hi hi).

Terry
KI7M

> On August 15, 2018 at 6:50 AM Matt 
> 
> 
> Hi Terry,
> 
> If you are going with light elements, as I believe I read in your posts,
> then truss cables can be used to help stabilize the elements both in the
> vertical and horizontal planes.   There is a small diameter Phillystran
> available that works very well for this duty.    Truss cables are typically
> supported from both ends of a horizontal bar mounted above and parallel to
> the boom at each element.   The opposing mechanical loads on the bar from
> both sides of the element help cancel out the bending stresses on the bar.
> Most designs I have seen use a bar length of 24" or more mounted about 6" to
> 12" above the boom.  The cables are attached to the elements about half way
> out from the boom to the element tips.
> 
> As I'm sure you are aware, popular shortening options include capacitance
> hats, linear loading, and base coil loading - in typical order of decreasing
> efficiency.   I believe you will find that about 45' width is a practical
> minimum for a shortened element on 40m.     One interesting option is that
> with linear loading, it's possible to support the elements with metallic
> truss wires which do double duty for electrical loading without adding
> weight to the ends of the elements, but be sure to use wire that won't yield
> (stretch) over time such as Copperweld.   This option will require some
> short segments of non-metallic (typically fiberglass rod) component in the
> element construction at the loading wire attachment points.  The loading
> wires will also need to be electrically isolated from the boom via the truss
> support bar.   Element tuning is accomplished by varying the position of a
> shorting strap placed between the two support wires back on the boom side of
> the arrangement.
> 
> The big tradeoff for shortened 40 is the decrease in performance
> bandwidth...  particularly F/B ratio, which can be rather dramatic if you
> are trying to cover both the CW & phone segments with one antenna.    IMHO,
> the Moxon design provides a much better overall compromise in terms of
> performance bandwidth for a shortened 40 antenna.   There has been a lot of
> discussion on this reflector about this subject in past years so you may
> want to look in the reflector archives for ideas.
> 
> Hope this info is of help and good luck on your project.
> 
> 73
> Matt
> KM5VI
> 
> 
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of terry
> burge
> Sent: Wednesday, August 15, 2018 1:06 AM
> To: towertalk at contesting.com; Grant Saviers <grants2 at pacbell.net>; terry
> burge <ki7m at comcast.net>
> Subject: Re: [TowerTalk] supporting a 40 meter rotatable dipole with trusses
> 
> Well, OK you got me redesigning my little project. Don't know yet how I will
> change it or just start over again. I do have the 1.50" X 0.120 heavy wall
> also 6' long. And I am considering how I could utilize some coils and/or
> capacitance hat arrangements to shorten up the antenna. Closer to what I
> suppose a shorty forty or something like that. One problem is I just haven't
> been up close to a 40 meter beam to get a decent idea what I am really
> dealing with. I know when I tried to raise this one above my head probably a
> good 1/4 to 1/3 of the outer elements were still on the ground. That before
> any kind of serious trussing. Might even go back to the design like in QST
> antenna issue a couple years ago with weighted wires hanging off the ends.
> But I would prefer something more stable than that.
> 
> Terry
> KI7M
> 
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