[600MRG] For discussion: Re: Top loading a vertical on LF/MF

[John Langridge]

Neil,

Let me relate some personal experience:

my first 80/160 antenna at this location was 45 feet tall with 4 umbrella wires that brought the natural resonance of the vertical to the bottom of the 80m band.  I used a coil on 160.  The ends of umbrella wires were probably 25 feet above the ground.  Those umbrella wires were greater than 45 degrees with respect to the vertical element but without running the numbers again, I don't recall how much.  At the time there was a lot of discussion about this on the topband reflector and the consensus was reached that 45 degrees was the magic number.  Any less than that and you probably had too much cancellation. I will have to check the archives over there to see if I can find the exact references but I'm not sure if there was any hard math associated with those values.  It was likely on air performance that drove a lot of that.

The antenna worked well and certainly much better than if there were no top loading at all.

It was not until I went to truly horizontal toploading wires that I realized just how much better it could be.  It was a big difference on TX, or that was my perception but its always tough to quantify those numbers when conditions  are constantly changing.  "Ground wave" seemed to show a significant increase in performance so it stands to reason that the skywave mode improved as well.  No doubt some cancellation can happen on sloping wires if they are too long or slope too drastically.

SO is the top loading necessary - yeah, I would say anything you can get in the air at the top of the vertical element, there is probably some benefit.  It would be a shame not to have some toploading.  Look at your slope angles... If they are not too drastic, you probably don't have a lot of cancellation to contend with.

After having horizontal T wires for 630m and a "taller" vertical element, I can't imagine going back to sloping wires unless I absolutely had to but I also can't imagine operating without any top loading.  Thats almost like free money.  As ON4UN says in the lowband dx book, its the only lossless loading method (minus conductor losses).

Hopefully that gives you some food for thought.  Figure out the angles and that will help you decide.

73,

John KB5NJD/WG2XIQ




________________________________
 From: Neil Klagge <w0yse.7 at gmail.com>
To: 600mrg at w7ekb.com 
Sent: Wednesday, November 27, 2013 5:18 PM
Subject: [600MRG] For discussion: Re: Top loading a vertical on LF/MF
 

To the 600m gang:
The reason for initiating this discussion is that, for me and perhaps
others, it is not feasible or possible to add top loading wires to a 630m
vertical without sloping the load wires downward a considerable amount.

I know that when an antenna is “folded back on itself” there is
cancellation of some of the radiation from the antenna. This is certainly
the case for top loading wires that reach toward the ground down to less
than half of the height of the vertical section.

The question I find myself asking is this: “Is what I will gain in ERP
worth the effort it takes to add sloping top wires because of the
cancellation that will occur.” I wonder if 1 or 2 dB gain is worth it at
the receiving end.

I would be interested in feedback from those who have any experience with
both situations: Namely, top loaded verticals and “topless” verticals  ;-)

73, Neil Klagge, WG2XSV, W0YSE


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