[600MRG] Free standing verticals

Thu Feb 8 10:30:20 EST 2018

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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