1. Main vertical element length, due to using the 1" CP how much shorter will it be compared to the standard formula 234/f.Mhz -5%= 31.75 ft
Try modeling this with the vertical element connected directly to MININEC ground.
That should get you close enough. But because there are always variables (such
as the ground characteristics, stray reactances in the antenna mount and feedopint,
etc.) you still probably want the ability to adjust the length with a telescoping joint.
But an observation: where did the "-5%" come from in your formula? Generally the
formula is simply given as "234/f", which includes a 5% end correction. The standard
formula length is about 33.4', and I wouldn't expect you to end up more than a foot
shorter than that when using 1" pipe.
Here's a reasonable estimate, however: I used W9CF online yagi modeller:
http://fermi.la.asu.edu/w9cf/yagipub/index.htmlto find the resonant length of a 40m dipole (treating it as a single element yagi).
For #10 wire it was 67.5'. For 1" diameter tubing it was 65.75'. The equivalent
half lengths for a ground-mounted vertical would be 33.75' and 32.875' - so not
quite a foot shorter for the fatter element, and still closer to 33' than to 31.75'.
2. What is the appropriate mounting height above ground for the bottom of the vertical element, my tolerances are 2"-30"
If the radials are laying on the ground and connected by a single wire to the
feedpoint, then the length of that wire between the feedpoint and the radials
will add to the effective length of the antenna. Your best options are either to
put the feedpoint as close as possible to the ground (say within 6" or so), or to
angle the wires from the feedpoint down to the ground and then out along
the ground.
3. Should or IS there a way to make the vertical radiating element more efficient and resonate on the bands other than 40m by way of structural design.
--3a. My idea was to add more conductive metal by way of CP couplers along the length of the radiating element placed 1/4w from the bottom of the radiating element in their freq. dependent locations. For lack of better terms I have chosen to name these "Sleeve Traps" . Is this a feasible idea that needs expanded upon or has it already been done??? maybe I have the next "Big Idea" hihihi.
You can certainly get it to work on 15m, with perhaps the addition of some capacity
hats at various locations. That will be as a 3/4 wave mode, which isn't ideal, but isn't
really that much worse than a 1/4 wave in practice. For those two bands you can feed
it directly with coax.
If you look at pictures of the 18HT "Hightower" vertical you'll see that it uses "decoupling
stubs" to enable it to work multiple bands. I think these are 1/4 wave stubs running parallel
to the main radiator, with the base 1/2 wave up from the bottom of the antenna. If so,
the antenna would be operating in 3/4 wave mode on the added bands. In your case this
won't help you on the bands below 15m, but you can try that technique on 12m and 10m.
One problem with using "decoupling sleeves" is that they should be 1/4 wave long at the
resonant frequency, and the ones for adjacent bands will overlap. You might manage
something similar using open stubs of copper pipe running parallel to the main upright,
which would allow multiple ones to overlap, but that still means that your 20m stub
goes all the way to the top of the antenna, and you can't use that method on 30m.
Besides designing the antenna to include traps, two of the better approaches have
been used in commercial antennas:
a) B & W marketed a vertical that used 3 verticals arranged in a triangle (by attaching
them to the outside of slices of large diameter plastic pipe. One worked 40m and 15m
using capacity hats, the second worked 30m and 10m using a similar approach, and the
third was an 80m element with a loading coil that acted as a 20m trap. (Or something
like that -
never let the facts stand in the way of a good story.)
b) The current "Hightower Jr" vertical uses what is basically a 40m vertical up the center
with cross-arms that hold quarter wave wires for most of the higher bands. So, for
example, you can use the main radiator on 40 / 15m, with wires for 10m, 12m, 17m and
20m supported by the crossbars. (The actual antenna also runs a 80m loading stub
around the ends of the crossbars.) All the radiators connect in parallel to the feedpoint,
allowing direct coax feed on all bands.
Another common approach is to use a straight vertical with a remote autotuner at the
base to match it on multiple bands: in this case companies such as S9 make the
antenna slightly short of resonance on 40m so that it doesn't present an unacceptably
high impedance on 20m and 10m.
If you only want two bands, such as 40m and 20m, then a simple matching network with
a coil and two capacitors at the base will give a low SWR using it as a quarter wave on
40m and a half wave on 20m.
4. Should there be circular radial elements connected and/or included in the design of the ground plane, or at very least a "encircling wire element" that ties all far ends of the 128 GP together.
Shouldn't matter. I'd leave it off. The only such wire I would use is right around the
base to connect all the radial wires to.
--4a I have seen and heard conflicting information on this concerning the received noise level. As in by adding the "encircling element" significantly increased the level of received noise and interference.
If you have enough current flowing at the far end of your radials for that to make a
difference, they aren't long enough.
5. HOW! does one feed such a monster, I would prefer something that did not require adjustment at the antenna and as stated previously I will be using an "L" network turner with built-in balun for balanced feeders and single wire against ground in the shack. What is the most efficient and loss-less method, is their a way other than my considerations below.
The methods I proposed use direct coax feed. I don't think there is any advantage in
using open wire line, but if you want to, I'd put a balun at the base of the antenna and
connect the open wire line to the balanced terminals.
--5a. I have considered the following: 1 ground the vertical element and use a shunt feed that is common on towers for 160m with coax, I believe these require adjustment at the antenna, that is not desirable in this instance
Shunt feed can work well for one band when the antenna is near quarter wave resonance.
It isn't generally a good approach to multiband operation.
. 2 use a shunt coil at the feed point with coax ( my reasoning behind this is to bleed static noise from the antenna by holding it at d.c ground potential )
Not a bad idea to have a shunt coil, or at least a resistor or choke, to ground. If the
input impedance is low on all bands then you can use the shunt coil as part of your
matching network on 40m (which requires a change in the antenna length) but
otherwise you run into problem with the high feedpoint impedance on 20m and 10m.
A 100K 10W wire wound resistor may be a suitable alternative.
While this will drain static
electric charges from the antenna, that isn't the same
as draining static
noise. I don't expect that a DC ground will make any difference
in the receive noise level in most cases. It might eliminate the annoying pops in the
receiver when the static electricity build-up causes the capacitor to arc in your
antenna tuner.
3. using a balanced 450ohm feeder with one side connected to ground.
Generally not a good idea.
4. using a guanella current balun of either 1:1 or 4:1, or less preferred would be a ruthroff voltage balun 1:1 or 4:1 with coax and one side of the balun connected to ground
You have an unbalanced antenna and unbalanced feedline - why would you want a
balun there?
If you are feeding a fixed-length vertical (generally chosen so it is NOT resonant on
any operating frequency) then in some cases a 4 : 1 UN-UN (unbalanced to unbalanced)
may reduce the losses due to high SWR on some bands. (That doesn't mean that the
losses are
LOW, just that they aren't quite as high as they might otherwise be.)
5. using 50ohm coax with a "coaxial common mode choke" aka The famous ugly balun...
You're confusing two different concepts.
With the large radial system you are proposing you shouldn't have much problem
with common mode current, but there might be a little bit due to direct pickup
on the coax. In that case a "coaxial common mode choke" aka "CURRENT BALUN"
may be helpful.
This can take the form of a coil of coax, but winding a shorter length of coax
on a high permeability ferrite core will usually give better results over a wider
bandwidth. Of course, this works best when the antenna presents a low SWR
to 50 ohms on most bands of operation.
There are a few additional points to consider. First, as you make the antenna
longer the efficiency will improve on 80m and 40m, even if the antenna is no
longer resonant. On the other hand, performance drops off when an antenna
is functionally longer than 5/8 to 3/4 wavelength, which limits the range of
frequencies over which a continuous conductor will work well, even without
regarding the impedance match.
