Steve, et al.

I performed the test described below on my 20-15-10-06 BB hex beam. This is one
built using the coaxial cable segments between the element feed points.

While checking return loss over freqeuency and looking for any obvious common
mode current issues, I moved a metal pipe in and around the center mast
structure while grounding it various ways. The good news is I found very few
observable effects while the vertical pipe entered the near-field region of the
center mast and the coaxial feed segments. Not until the pipe was directly next
to the feeder did effects become apparent, albeit very small ones.

As a control, I moved the pipe near and along the elements and saw plenty of
disturbance... as would be expected.

This matches up well with simulations. More tests are in order to ensure common
mode currents are not promoted.

For me at least, this is some seriously good news. Now I have hope I can
Christmas Tree a 2 meter antenna above the hex and still have height available
for more robust lightning tolerance... an important issue at my QTH.

Thanks again Steve for a design that has, at least for the moment, passed
another evolutionary requirement.

John

--- In hex-beam@yahoogroups.com, "John Huggins" <john@...> wrote:
>
>
> I'm about all "theory'ed" out for the moment and a hands on test is in order.
>
> There is a quick test many of us can do pertaining to the coaxial feedline
> version of the hex beam feed system.
>
> With analyzer attached (or better yet a VNA) move a vertical metal mast or
> similar long metal object near and around the vertical feed point and see
> if there is an appreciable effect on analyzer readings.
>
> Next, rub your hand along the coax elements while viewing the analyzer at
> the frequencies of interest. This will, of course, be hard to do without
> your whole body also causing interactions, but the more nimble of us
> should be able to do A/B comparisons with the delta being only hand
> movements.
>
> My hex beam is not in "testing" position so my testing will come later.
> Some of you might be in a better situation to try this sooner.
>
> The goal here is to see how "touchy" the outside of the coax band
> interconnects are in the various bands. If the hand and/or metal cause a
> change, then we have something to think through if we are to use a metal
> mast for the hexbeam.
>
> I suspect, like others, there will be an interaction. However, the truth
> is out there.
>
> John
>
> > Thanks Al,
> >
> >
> >
> > My comment about the similarity between the Yagi and a Hexbeam or an
> > OctoBeam with regard to a parallel coax feed system was made only to
> > suggest
> > that a metal center post probably could be used with minimal effects on
> > the
> > antenna as far as coupling with the elements is concerned. Although
> > considerations for common mode current issues should be considered I think
> > electrical isolation by insulation of the metal center post should solve
> > that problem. I should have mentioned the difference in the orientation
> > of
> > the feeders relative to the beam direction for the antennas though and
> > only
> > thought about that afterward. The Log periodic or Log-Yagi arrangement
> > for
> > example has a feeder system parallel to and within close proximity of a
> > metal boom. This is the specific example I was referring to, and in that
> > case the feeder system is parallel to the direction of radiation, whereas
> > an
> > OctoBeam or Hexbeam has a feed system perpendicular to the direction of
> > radiation.
> >
> >
> >
> > I believe I'll add another project to my list of things to experiment
> > with.
> > Hopefully, I can report good results from an all metal center post
> > implementation.
> >
> >
> >
> > 73!
> >
> > Bill, KO6HL
> >
> > http://www.NorCalMfg.com <http://www.norcalmfg.com/>
> >
> > http://www.OctoBeam.com <http://www.octobeam.com/>
> >
> >
> >
> > _____
> >
> > From: hex-beam@yahoogroups.com [mailto:hex-beam@yahoogroups.com] On Behalf
> > Of k8eur
> > Sent: Friday, August 27, 2010 1:54 PM
> > To: hex-beam@yahoogroups.com
> > Subject: [hex-beam] Re: Contiuous metal mast through hex beam to VHF
> > antennas above hex
> >
> >
> >
> >
> >
> > Bill, the issue here is common mode currents AND coupling of the
> > multiple-tapped coax feeder system of the hexbeam to a metal mast.
> >
> > At that point there is no correlation between coaxial cable taped to the
> > boom of yagi and connected to the single driven element feedpoint ......
> > and
> > the hybrid coaxial feed system connecting 5 driven elements of a hexbeam.
> >
> > The coax ceases being a transmission line at the hexbeam feedpoint. The
> > coupling of mast current to the complex unbalanced coaxial 5-band feeder
> > is
> > where the problem manifests itself. A non-metallic center post is used on
> > the hexbeam to minimize some of these problems. This is another reason why
> > a
> > choke balun always belongs at any antenna feedpoint.
> >
> > We do not dismiss the effects of common mode currents and we do not accept
> > pattern skewing and distortion.
> >
> > The BB hex antenna by G3TXQ is the result of much modeling and testing and
> > we feel that too much tinkering can only result in less performance than
> > Steve's design (and our testing) promises. While unusual, the BB hex is
> > not
> > magic and still follows the laws of physics. I feel we need to understand
> > and obey those laws.
> >
> > That being said, I am sure that any type of array can be built around,
> > above
> > and below any type of antenna and it will produce some kind of acceptable
> > results to the user - but not optimum results.
> >
> > Experimentation is encouraged in amateur radio. It is a valid learning
> > process. Unfortunately, antenna performance is difficult for most to
> > measure
> > in the field. It is important that people like G3TXQ have taken the time
> > to
> > do a lot of the experimentation for us, and then to have shared it all
> > with
> > us!
> >
> > 73,
> >
> > Al - K8EUR
> >
> > --- In hex-beam@yahoogroups.com <mailto:hex-beam%40yahoogroups.com> , "BG"
> > <ko6hl@> wrote:
> >>
> >> Thanks John,
> >>
> >>
> >>
> >> I had not previously considered a length of coax parallel to and in
> > contact
> >> with the boom on a Yagi antenna and the use of a metal center post with
> >> parallel coax feeder to be similar, but in fact they are.
> >>
> >>
> >>
> >> 73!
> >>
> >> Bill, KO6HL
> >>
> >>
> >>
> >> _____
> >>
> >> From: hex-beam@yahoogroups.com <mailto:hex-beam%40yahoogroups.com>
> > [mailto:hex-beam@yahoogroups.com <mailto:hex-beam%40yahoogroups.com> ] On
> > Behalf
> >> Of John Huggins
> >> Sent: Thursday, August 26, 2010 1:08 PM
> >> To: hex-beam@yahoogroups.com <mailto:hex-beam%40yahoogroups.com>
> >> Cc: hex-beam@yahoogroups.com <mailto:hex-beam%40yahoogroups.com>
> >> Subject: Re: [hex-beam] Re: Contiuous metal mast through hex beam to VHF
> >> antennas above hex
> >>
> >>
> >>
> >>
> >>
> >> > John,
> >> >
> >> > The only problems I foresee would be possible interaction with the
> >> > inter-band transmission lines.
> >>
> >> Agreed Steve. Using your HB EZNEC file, the one with inert TLs as
> >> interconnections, I positioned a vertical pipe a bit off center (a few
> >> cm
> >> away from the feed points) and ran the simulations. As logic might
> >> dictate, the orthogonal nature of vertical pipe and horizontal antenna
> >> elements suggest a large conductor running through the middle of the HB
> >> is
> >> not hopelessly ridiculous. Of course, wires sag and angles are often not
> >> quite 90 degrees, but the basics seems to hold up as they have for
> >> decades
> >> with horizontal Yagi-Uda antennas strapped to vertical structures.
> >>
> >> >
> >> > In the case of the Traffie and DXE beams, the transmission lines are
> >> > balanced. I don't know how far the fields extend around those TLs, but
> >> > it's possible there may be some effect from a conductor placed very
> > close
> >> > by.
> >>
> >> Yes... changing the TLs to interconnected parallel lines reveals the
> >> effects of the vertical pipe more dramatically. Keeping the parallel
> >> conductors 10x the wire separation distance is a rule of thumb I have
> >> heard. Of course if the currents are nicely equal and opposite in the
> >> parallel line, things should be better all around.
> >>
> >> >
> >> > It's also possible that running the main coax feedline alongside an
> >> > extended metal Centre Post could provide a common-mode path which
> >> > by-passes any choke.
> >>
> >> Good point and another good reason for the choke to be at the top.
> >>
> >> >
> >> > I've no way of quantifying those effects; my guess is they are
> >> probably
> >> > small.
> >>
> >> Indeed we might be worrying about small percentages. However, the goal
> >> of
> >> making the HB functional in a stacked antenna environment is well worth
> >> the discussion. Thank you as always for the dialog.
> >>
> >> 73
> >> John, kx4o
> >>
> >> >
> >> > 73,
> >> > Steve G3TXQ
> >> >
> >> >
> >> >
> >> >
> >> >
> >> > --- In hex-beam@yahoogroups.com <mailto:hex-beam%40yahoogroups.com>
> > <mailto:hex-beam%40yahoogroups.com> ,
> >> "jhuggins64" <john@> wrote:
> >> >>
> >> >> Steve, Leo and all,
> >> >>
> >> >> All this discussion about high stress points in the hex construction
> >> >> reminds me of a question I have been waiting to ask this group.
> >> >>
> >> >> Are there any pitfalls to using a metal mast, say 15 feet of 1-1/2"
> >> OD,
> >> >> from rotor, through thrust bearing, through hex beam hub, past hex
> >> beam
> >> >> feed system and up to antennas well above the hex?
> >> >>
> >> >>
> >> >> /-/-/-/-/
> >> >> |
> >> >> |
> >> >> | <- Can this mast be all metal top...
> >> >> |
> >> >> |----------|----------|
> >> >> \ | /
> >> >> \--------|--------/
> >> >> \-------|-------/
> >> >> \-----|-----/
> >> >> \---|---/
> >> >> ==> | <- ...to bottom?
> >> >> |
> >> >> /+\
> >> >> | | |
> >> >> | | |
> >> >> | | |
> >> >> |(+)|
> >> >> |===|
> >> >>
> >> >> Thanks.
> >> >> John
> >> >>
> >> >
> >> >
> >> >
> >>
> >>
> >>
> >> No virus found in this incoming message.
> >> Checked by AVG - www.avg.com
> >> Version: 9.0.851 / Virus Database: 271.1.1/3094 - Release Date: 08/25/10
> >> 23:34:00
> >>
> >>
> >>
> >>
> >> [Non-text portions of this message have been removed]
> >>
> >
> >
> >
> > No virus found in this incoming message.
> > Checked by AVG - www.avg.com
> > Version: 9.0.851 / Virus Database: 271.1.1/3097 - Release Date: 08/26/10
> > 23:34:00
> >
> >
> >
> >
> > [Non-text portions of this message have been removed]
> >
> >
>