[600MRG] Free standing verticals

Thu Feb 8 13:38:32 EST 2018

		let me add a twist. Consider utility poles. It is not an obvious choice unless you’ve worked with them (I have). They are not that expensive and very wind resistant while capable of carrying a fairly substantial load. A 40 footer typically provides about 34 feet above ground height while a 60 footer can provide 50 feet or more. I have used them in the past and the US military built many 50 watt AM radio stations with those as masts along similar lines of Mr. Smith’s designs.  While not an option for everyone, it is worth consideration in certain situations. 

		Sent from my iPad
	_____________________________
From: Mike Irizarry <michael.irizarry29 at gmail.com>
Sent: Thursday, February 8, 2018 10:50 AM
Subject: Re: [600MRG] Free standing verticals
To: Brian Pease <bpease2 at myfairpoint.net>
Cc:  <600mrg at mailman.qth.net>

Check this design out. You good use a 40 foot fiberglass push up mast to build something similar. Picture is in the link. Looks like 43 foot mast.

Carl E. Smith has now described (IEEE Trans. on Broadcasting, June 1989, pages 237-240) a modified short low-loss AM antenna and explores ways in which the performance of relatively small transmitting or receiving antenna systems can be improved. He writes: "Small AM antennas are useful for standby use when the regular antenna fails for some reason. With some modification of a short tower by using top loading, low-loss loading inductances and an insulated counterpoise, the performance can be made quite acceptable. The counterpoise is connected as shown in the illustration. The inductance +jx4 is tuned so as to maximise the field strength radiated by the antenna into the far field... Top loading raises the current loop on the tower and, by adding a low-loss inductance at the top of the tower, the current loop is raised still higher on the tower. A low-loss inductance at the top of the tower can be achieved by insulating a suitable conductor inside the tower and shorting it to the tower to simulate a short-circulated coaxial line with the open and inner conductor connected to the top loading hat at the top of the tower... At the bottom of the tower, more series inductance can be added by insulating a conductor up inside the tower to a shorting point. It may also be necessary to add a low-loss base loading-coil to resonate the top hat with the counterpoise... The counterpoise potential is adjusted to minimize ground losses."

Dr James F. Corum of Corum & Associates Inc. believes that "The Smith/Musselman low-loss tuned-counterpoise structure is a remarkable addition to the technology of electrically-small antennas... it represents a significant contribution to this branch of antenna engineering. We think that anyone requiring a vertical stub with an abbreviated ground system should seriously consider this technology." It is clear from the paper that results are highly dependent upon correct tuning of the counterpoise system, preferably while observing the far-zone field strength. At the Corum test facility at Windsor, Ohio, a Smith/Musselman radiator resonating on 1330kHz had a tower height of 43ft, a top hat of 24 horizontal radials 50ft long, a counterpoise of 24-50 radials 12ft above ground and soil conductivity of 8 millimhos per metre, producing a field strength at 1 mile of 1.1mV/m with 250mW input with the counterpoise tuned, dropping to 605p.V/m without the tuned counterpoise.
http://www.robkalmeijer.nl/techniek/electronica/electronicabladen/ew_ww/1990/02/page169/index.html

On Thu, Feb 8, 2018 at 9:23 AM, Brian Pease <bpease2 at myfairpoint.net> wrote:
              One cheap method to get some height is to mount a 10-12 ft piece of    Sch 40 large dia PVC pipe on your post with a short adapter or    shimming on top to fit a tall (say 30 ft) lightweight carbon fiber    fishing pole/kite pole on top, which just drops in.  The trick is to    run a wire INSIDE the kite pole attached at the top and run right    out the bottom and through the PVC pipe.  A light horizontal wire    can run to your other pole.  This should be self supporting although    it will bend towards the house.  I think the main problem would be    breaking of the horizontal wire in high winds.  An light guy line    (or wire) run from the top to the neighbor's house might help.
    I also have used electrical tape on each joint when extending the    kite pole to prevent collapsing.
    Depending on soil conditions, I would consider enlarging the bottom    of the post hole and packing in a bag (80 lbs) of mixed QuickCrete.     I installed >20 8 ft sign posts this fall.

    On 2/8/2018 12:10 AM, Ben Gelb wrote:
              Thanks all for the replies.        
                Yard is 30' wide by perhaps 45' deep behind my rental house          in San Francisco. There is one tree of substantial height (the          one thats going away) on one corner of the yard (up against          mine and my neighbor's house on the east side of me). That          currently gives me about 30' of vertical for my inverted L,          and then I have a fiberglass fishing pole supporting the end          of the top-hat about 30' away from the vertical. (this          inverted L is my only transmitting antenna currently, but for          MF and HF - I also have a couple of small receiving loops on a          rotatable base at ground level)        
                With the tree gone will need to provide my own structure,          and I would prefer to avoid a lot of guying if possible, as          there's not a lot of room for it, and it will really consume          the entire yard. I was thinking to sink a 4x4 or 6x6 post into          the ground (i have a post-hole digger) and then maybe attach          some sort of mast to it, hopefully stiff enough to not need          any guying (or at least not much). Alternatively, the DX          Engineering MBVA-5A looks like it might be a reasonable          option, albeit perhaps a bit more expensive than some          home-depot option (ostensibly it doesn't require guying).        
                If I were to kludge up some set of metal pipes and tubes, I          wonder how I might mount it to a wooden post - I'm thinking a          wooden post might not be a great dielectric (tree sure wasn't)          and might lead to some burning. Anybody tackled that problem?        
                I do have some of the 4' military mast sections (mine are          aluminum not fiberglass though) but I think they'll get pretty          floppy over 15-20' or so w/o some guying...        
                Neighbor mentioned being open to draping a wire over his          house if it helped.... but I think more useful would be          expanding the radial field throughout his backyard... haven't          broached that subject. He might be less excited about that.        

        On Wed, Feb 7, 2018 at 5:35 AM, Dave          Riley <dave.riley3 at verizon.net>          wrote:
          Hello Ben,

            Can you give us more info concerning your real estate plot            such as square footage, relationship to power lines,            existing antennas, size and height of your home, any            neighbors who would allow you to span their property, or any            obstructions that would be in the way of an antenna and            lastly what you have for antennas for ham use at this time?

            Are you presently using any sort of loop or probe antenna            for receive?

            All the answers to your quest so far sound workable so maybe            a mix or some kind of a modification could allow you to            enjoy the new band.

            Thanks from DaveR @ aa1a

              On 2/4/2018 7:11 PM, Ben Gelb wrote:
                                                                        My neighbor is taking down my antenna tree ...                  possibly this week :(.

                  Its actually the right thing - the tree is very                  unbalanced and needs to go. But it means my undersized                  antenna will be even smaller (gone) soon...

                  Seems like I may need to try to get something in the                  air that doesn't require a tree or permanent support                  structure. I can probably fashion some kind of                  vertical pole out of cheap materials, but imagine it                  will require a lot of guys to remain vertical - which                  I'd kind of like to avoid since I don't have a lot of                  room for guys.

                  Any suggestions from this group?

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