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Author Topic: 40M vertical, help desperately needed, u may need coffee (just saying)  (Read 2034 times)
KD8TGK
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Posts: 6




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« on: February 12, 2013, 02:45:08 PM »

Hello, KD8TGK, Michael Householder here and I'm new to the forum, and I am desperately seeking help in the construction details of a 40M ground mounted vertical ground plane antenna which I have modeled after AM commercial broadcast standards in the U.S.A.
I do want this to be a multi-band  antenna to cover 40M-10M mainly and if my MFJ differential tuner (mfj-986) can load it on 80m and 6m all the better. Also my output power is 100w MAX!

The Idea henceforth follows as:

Design frequency. 7.000 mhz

1. A 1/4w vertical radiator made from 1" Copper Pipe (CP for short) mounted at the base within 2"-30" above ground, and the mounting height is variable within the measurements, and isolated from ground.
2. The ground component shall consist of 128 1/4w ground radials, laying on the ground, coming straight away from center in the usual X fashion, held in place with landscaping "staples", the wire is AWG20ga solid conductor and yes I have 4,000+ ft of it. In addition to 1- 8ft ground rod driven into the soil at the center of the GP

Now before I start with the problems I am having, I have attempted to use 4nec2, ARRL NECv4.0, MMANA-GAL-basic, and EZNECv5.0demo to model this antenna to no avail, I am completely and utter programming defunct and partly dyslexic when it comes to X,Y,and Z axis which is used for modeling, and for some unknown reason I have other issues with the programming. in addition I have attempted to create this antenna using and mutilating preset antenna examples and I run out of segmenting in EZNECv5.0demo in addition unable to transfer or recreate the design in the other software.

I know this antenna sounds elementary and simple but that is not the case here, several questions have risen, which has led me to join this site and start this topic.

Questions are as follows:

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
2. What is the appropriate mounting height above ground for the bottom of the vertical element, my tolerances are 2"-30"
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.
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.
--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.
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.   
--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 . 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 )  3. using a balanced 450ohm feeder with one side connected to ground. 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  5. using 50ohm coax with a "coaxial common mode choke" aka The famous ugly balun... and im sure this part of this question alone will stir controversy. I have done much exhaustive research on these and their are a few points I would like to state. 1 they are frequency dependent and vary depending upon construction, also as u move out of the "band" of frequency of minimum effective choking impedance (10x-20x original coaxial feed-line impedance) they get very ineffective and allow your feed-line to radiate.

So that's about it. First I would like to thank anyone reading this and for any helpful input. Second if I have stated anything incorrectly or have any wrong information please let me know. I do have an mfj 269 antenna analyzer to aid during installation but my purpose here is to save me time, money, and the headache of stating in the wrong places including the waste of monetary resources while just throwing metal in the air and cutting to fit and still windup unhappy with performance, the rough cost is around $400 in materials alone. And finally please, please dont harass my madness about the 128 ground radials, there is sound reasoning and practice behind this, as anyone that has investigated thoroughly would know. As u decease the number of grounds and when u exceed .4 wave in length as I will be doing on all bands 20m and up, without sufficient number of ground radials, u will greatly vary the angle of radiation, along with decreasing the effectiveness of the plane, in addition to effecting feed-point impedance and over-all performance of the whole antenna system. By having a sufficient number of ground radials IMHO a minimum of 32 or more u can cancel out the negative effect on performance when the plane becomes non-resonate at various frequencies. Unless u live on a big metal plate like we all do when dreaming dreams of antennas! 73's and thanks for all the help. 
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N4JTE
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Posts: 1147




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« Reply #1 on: February 12, 2013, 03:42:21 PM »

No way am I gonna handle all the points you raise but a few can be addressed.
If your radials are on the ground, so should your vertical be, forget the 2in to 30in constraint. just a few inches up at the feedpoint will be the usual approach.
The copper pipe idea is not worth the effort or expense, at 35 ft a wire on a fiberglass pole will be better and more durable.
Making a 40 vertical efficent on the upper bands will need a remote tuner and mucho radials, and will not be something to write home about due to the various patterns developed and of course the major mismatch the tuner is cooking toast with.
You feed a vertical very simply, center conductor to the vertical, coax braid to the common point of all the radials.
Also, lose the modeling approach, I have built many advanced verticals, phased, 4 squares etc. the only thing a modeling program can supply is some inkling of pattern and impedance.
Others will respond with further info but the basics are presented and I suggest you hit some books like the ARRL antenna books etc, open up a whole new world. Build it then see what happens.
Bob
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WB6BYU
Member

Posts: 12982




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« Reply #2 on: February 12, 2013, 04:09:04 PM »

Quote from: KD8TGK

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.html
to 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'.



Quote

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.



Quote

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.



Quote

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.


Quote

--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.



Quote

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.



Quote

--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.


Quote
. 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.




Quote

3. using a balanced 450ohm feeder with one side connected to ground.



Generally not a good idea.


Quote

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.)


Quote

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.
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KB4QAA
Member

Posts: 2241




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« Reply #3 on: February 12, 2013, 05:22:41 PM »

Well, you are nothing if not ambitious and thoughtful!

-The way to provide multiband operation is to add traps.  Or, in other words, buy a vertical from HyGain or Hustler, and make best use of your excellent radial field.

-LaPorte advises against adding cross connections in radial fields to avoid hysteresis currents.

-Every inch you add above the radial field/ground is essentially like adding that length to your antenna and detuning it.

-Ideally the tuner/match should be at the feed point, in order to minimize losses in the coax.  You must look at the numbers and convenience and choose your trade offs.

-Operating an antenna below its' resonant frequency will greatly increase voltages in your tuner.  Just be aware.

-If you are working from formulas, stay with it, e.g. 234/f = length.  Don't go adding/subtracting other random percentages.

-A vertical is a Unbalanced antenna.  Keep things simple and feed it with coax which is also Unbalanced.  If you want to add a 1:1 isolator in the feedline close to the feed point that is fine.  A RF choke for DC grounding the antenna is a good idea to bleed off static electricity, and can make the antenna quieter.

Again, if you want great performance in a multiband vertical buy one of the traditional trapped models.  They will outperform an untrapped 'Plumbers' Special".
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N8NSN
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Posts: 283


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« Reply #4 on: February 12, 2013, 06:01:47 PM »

Looked you up on QRZ for an email address... None there. No worries. Was going to send you 40/80 meter ground plane schematics and photos of it... There will be an article here on eham very soon on it... It works great on 40 & 80 with no tuner and very well on 30 through 17 with a simple tuner... But I intended it for 40 & 75/80... It's a ground plane design, but the feed point is only 8 feet up. Austrailia etc on 40-regularly, all over Europe on 80, regularly.
Low take off angles and efficiency being the keys to DX. Vertical TX antennas very good for that. On 80 a shielded loop RX antenna is a good combo with the vertical TX antenna.  Anywho- hopefully the rditors will post the article soon.

By the way, the suggestion of a fiberglass mast with a wire attached to it is VERY good advise. That's the basis of the build here...

Best luck & 73
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KD8TGK
Member

Posts: 6




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« Reply #5 on: February 12, 2013, 10:41:26 PM »

Thank you N4JTE, for the recommendation of the mounting height. And my reasoning behind the 1" copper pipe for the element is to increase bandwidth. Originally I wanted to use something in the 6"-3" range but am unable to financially. I came up with these number from yagi modeling programs, several said the maximum diameter of a circular conductors is 8" on a 10M beam and more surface area = more bandwidth = more efficiency.

Also thank you WB6BYU, for your exhaustive explanations, very helpful.
So #1 I was under the impression the 234 for a 1/4w and 468 for a 1/2w dipole's and groundplanes was the standard calculation WITHOUT the end-effect reductions. #2-#4 i agree with,
#5 raises more questions
a.1 I agree and understand that,
a.2 gives me an idea, a shunt coil that is  multitapped and switchable at the feedpoint via remotely and utilizing latching relays with one side at ground and taps on 40-30-20-17-15-12-10-6 . I am under the impression that of course it will be resonate on 40m as a 1/4w is its design, in addition to being a 3/4 wave on 15; during operation of these 2 bands then only would i switch the shunt coil out also would i use the same coil tap for both bands or should they each have their own. Now am i correct in saying that 30m would be a 3/8 wave, 20 being a 1/2 wave, and 10 a full wave and 6 around 2 1/4 wave, by definition will these be the hardest bands to manage requiring its own tap for each? can I tap for 27.3 mhz and cover 12 and 10 on one tap, would i need a tap for 17 being so close to 15, what would be a better tune to minimize efficiency losses, tune at the antenna or in the shack , OR both.
a.3 understood but i had to ask
a.4 I see ur point I guess i was trying to make a unbalanced antenna balanced like a dipole by adding so much conductor to the ground plane component
a.5 basically I wanted to keep the feedline's outer skin from radiating and adding to the noise level , probably a coax coil at the feedpoint, and another at the end of the ground feid that way if any does resonate it is used in a fashionable manner
And thank you KB4QAA, because I did forget about the  hysteresis currents.
And finally at the time of this post, thank you  N8NSN, I did update my e-mail on qrz.com and I will check to see if its correct on arrl.org , so u can e-mail me now to send the schematics if u please would. I'm interested in seeing those.
Bye for now 73's KD8TGK
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W5DXP
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« Reply #6 on: February 13, 2013, 05:50:39 AM »

Just a couple of comments: VERT1.EZ that comes with EZNEC is a 40m vertical already designed. Just changing the frequency will allow one to see the radiation pattern and feedpoint impedance on the other bands.

IMO, the best way to feed a single element vertical used for multi-band operation is with an autotuner at the feedpoint. I've done that using an SG-230 on the following antenna for 40m-10m operation and it worked well.

http://www.w5dxp.com/vert4010.htm

A 1/4WL 40m vertical is a little too long for effective 10m operation because the take-off-angle is 36 degrees. For highest gain at lowest take-off-angle, a vertical should not be much more than 5/8WL long, i.e. 600/28.4 MHz = 21 feet for 10m.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W4HIJ
Member

Posts: 367




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« Reply #7 on: February 13, 2013, 01:10:17 PM »

FWIW, I run an S-9 31 ft vertical in an elevated ground plane configuration on 40 meters.  It's fed by coax through an " ugly balun" choke and it has three, quarter wavelength long tuned radials. The base of the antenna is right about 30 ft. of the ground. I have a tuner in the shack that I use to "touch up" the antenna at various points across the 40 meter band. I chose not to ground mount it and run radials because I'm lazy about such things and I didn't see much advantage it making is a so called " multiband antenna". You can get a ground mounted or even an elevated 40 meter vertical to take power on the higher bands with a tuner but my understanding is that the  line loss with coax  is pretty major.  There was an article in QST some years back about a wire ground plane suspended from a tree and fed with window line, I actually built it and fed it with twin lead.  Worked pretty dang well. I often think of changing the current feed arrangement of my S-9 to  window line. Sounds like an ambitious project you have. I'd get away from the copper though, as already mentioned the expense is bad.  Get a 31 FT. Jacktite pole and string a wire inside of it. That's all an S-9 like I have is anyway.
Michael, W4HIJ
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WB6BYU
Member

Posts: 12982




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« Reply #8 on: February 13, 2013, 01:13:07 PM »

Hope you have your coffee at hand...


Quote from: KD8TGK

... my reasoning behind the 1" copper pipe for the element is to increase bandwidth...



You can accomplish the same thing for much lower cost by using two or more
parallel wires spaced 6" or more apart.  (Might not even need that much.)


Quote

... and more surface area = more bandwidth = more efficiency.



Not really.  A fatter element does improve the operating bandwidth, but it isn't the
surface area that matters.  A pair of #14 wires spaced 48" apart has enough
bandwidth for a dipole to cover the whole 80m band, while a single strand of #8
(which has the same surface area) might only give a quarter - or less - of that.

But bandwidth probably is not a concern in this case.  Even using wire antennas
I don't remember ever having to worry about bandwith on 40m or any of the other
HF bands through 12m when using a full-sized antenna.  (160m, 80m, and 10m are
special cases.)  And if you need to use any sort of impedance matching (for example,
to match the high impedance on 20m) that may do more to set the antenna bandwidth
than the element diameter.

In the same way, surface area does reduce the RF resistance, which affects the
efficiency, but the actual difference for most antennas is quite small:  a dipole
might be over 95% efficient when made using #14 wire, and you'd never notice
the difference in radiated power if you eliminated all losses.  There are some
antennas with very low feedpoint impedances, such as the 8JK, some yagis, and
very short/small antennas (such as a mag loop or the DDRR) where conductor
losses can be significant, but that isn't an issue here when the antenna is 1/4 wave
on 40m to start with.



Quote

So #1 I was under the impression the 234 for a 1/4w and 468 for a 1/2w dipole's and groundplanes was the standard calculation WITHOUT the end-effect reductions.



The length of a half wavelength is 492/f.  The 468/f formula (which should only
be considered an estimate anyway) includes the 5% correct for end effect.




Quote

a.2 gives me an idea, a shunt coil that is  multitapped and switchable at the feedpoint via remotely and utilizing latching relays with one side at ground and taps on 40-30-20-17-15-12-10-6 . I am under the impression that of course it will be resonate on 40m as a 1/4w is its design, in addition to being a 3/4 wave on 15; during operation of these 2 bands then only would i switch the shunt coil out also would i use the same coil tap for both bands or should they each have their own. Now am i correct in saying that 30m would be a 3/8 wave, 20 being a 1/2 wave, and 10 a full wave and 6 around 2 1/4 wave, by definition will these be the hardest bands to manage requiring its own tap for each?



First, a shunt coil RAISES the feedpoint impedance.  It comes in handy if your
vertical has a feedpoint impedance of 35 ohms, or a yagi that might be 8 - 20 ohms,
for example.  It doesn't help you at all if you are trying to match 350 ohms, because
that starts out too high, not too low.

Similarly you can't match all bands with just a coil.  Well, I had a Hy-Gain 18V that
tried to do so, but the length was carefully chosen, and it didn't work all that well
on some bands.  

However, your basic approach is taking you in a useful direction.

For any length of radiator, you can determine (by measurement or modelling) the
input impedance on each band, then design a matching network to match that
impedance.  If you can switch the networks (either manually or remotely) then
you can get the antenna to load on each such band.  I like this approach when
I'm using a relatively permanent antenna:  I have a tuner box with a big bandswitch
and select coil and capacitor values to match each band.  Requires a bit of
fussing initially, but after that I can just turn the switch and the antenna is
matched without even transmitting.  (The modern approach, of course, is to
use an auto-tuner instead.)

This will generally require a separate switch position for each band, but you may
be able to double up in some cases (such as 40/15m), while for the wide bands
(160m, 80m, 10m) you may need multiple positions and/or a variable capacitor
or coil of some sort for fine tuning.

The most common matching circuit for such purposes is an "L" network, usually
constructed with a series coil and shunt capacitor (on the input or output), though
there are other options as well.  For example, if you find your vertical is ~35 ohms
on 40m, you can lengthen it until the resistive component reaches 50 ohms, then
add a series capacitor to tune out the inductive reactance that was added by
making it longer to get a good 50 ohm match.

Just because you can match the antenna on all bands doesn't mean that the
radiation pattern will be well suited to your needs, however.  Using your proposed
vertical on 80m will work to some extent, but at lower efficiency and narrower
bandwidth.  Above about 15m or so the angle of radiation will be too high and
most of your radiated power will be lost into space instead of reflected back
from the ionosphere.  Reducing the antenna length to about 20' will improve
performance on 10m, while increasing it to 40' will help on 80m.  You have to
decide, then, which bands are most important to you and size the antenna
accordingly, or use some method (such as traps or decoupling stubs) to change
the effective length of the antenna on different bands.



Quote

a.4 I see ur point I guess i was trying to make a unbalanced antenna balanced like a dipole by adding so much conductor to the ground plane component



That actually makes it more unbalanced.



Quote

a.5 basically I wanted to keep the feedline's outer skin from radiating and adding to the noise level , probably a coax coil at the feedpoint, and another at the end of the ground feid that way if any does resonate it is used in a fashionable manner



Yes, and that's not a bad idea.  My point was that there other types of feedline
chokes besides a coil of coax.  Sometimes simply burying the coax works well enough.

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KD8TGK
Member

Posts: 6




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« Reply #9 on: February 26, 2013, 10:16:05 PM »

Thanks alot for the "spaced wire tip" I have moved the design to be a "caged" radiator 42'ft long, circular in shape with 4 or 8 wires evenly spaced around a 6" circumference and the ground radial component of 120 radials, 50 ohm coax feed, and I'm now working on a manual antenna tuner system (PLEASE SEE: http://www.eham.net/ehamforum/smf/index.php/topic,88372.0.html ) placed at the feed point ( similar to SGC designs ). IMHO I do not think I am going to be able to get around not using a tuner at the feed-point. Using coax is the only practical feed-line to use, and it's not going to be a very efficient all HF band antenna due to coax mismatch losses at the feed-point on non-resonate bands. I feel that my tuner in the shack may be able to load and tune the antenna but losses at the feed-point will severely degrade antenna system performance probably almost to the point of using a dummy-load for DX on odd bands. Thanks everyone for their input and help, and any more would be greatly appreciated !!!!
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WA3SKN
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Posts: 5420




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« Reply #10 on: February 27, 2013, 08:33:55 AM »

OK, you have a good counterpoise... put it to use!
Instead of the "cage" concept, consider using separately cut vertical elements (half a fan dipole) and an auto tuner at the base.  You can make two elements for 40 meters if you want... the high end and the low end.  Since you have a tuner at the base, just use coax feed. The 30-40 ohm feed will be an easy match.
This will keep the signals at low angles.  If you try and load a 40 meter vertical element on 10 meters it will just act as a long wire and the pattern goes straight up, not the best for DX!
And since the coax will always be looking into near 50 ohms you will not have high mismatch losses.
Good luck with the project!
73s.

-Mike.
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WB6BYU
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Posts: 12982




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« Reply #11 on: February 27, 2013, 11:13:10 AM »

Quote from: KD8TGK

Thanks alot for the "spaced wire tip" I have moved the design to be a "caged" radiator 42'ft long, circular in shape with 4 or 8 wires evenly spaced around a 6" circumference...



Probably don't gain much using 8 wires unless you also increase the diameter. 
But I suspect you are near the point of diminishing returns, since your matching
network will determine the operating bandwidth more than the diameter.
The fatter element does, however, reduce the impedance variation around
half wave resonance, so might make it easier to match on 30m and 15m. 
Mechanically, 4 wires with wider spacing may be easier.


Quote

...IMHO I do not think I am going to be able to get around not using a tuner at the feed-point. Using coax is the only practical feed-line to use, and it's not going to be a very efficient all HF band antenna due to coax mismatch losses at the feed-point on non-resonate bands. I feel that my tuner in the shack may be able to load and tune the antenna but losses at the feed-point will severely degrade antenna system performance probably almost to the point of using a dummy-load for DX on odd bands.



Will the losses "severely degrade" your system?  The loss depends on the type
and length of coax you use, the feedpoint impedance and the operating
frequency.  With 100' of RG-213, you could have 6dB of loss on some bands, but
that still gives you more radiated power than many QRP stations who make plenty
of contacts.  It certainly isn't to the point of being a "dummy load" by any means,
even if it is a significant reduction.

That's not to say that you shouldn't consider the remote tuner option - it will
certainly reduce losses on many bands, and would be the appropriate choice if
you are trying to model typical AM BC installations (except that few AM BC
stations use radiators taller than 1/4 wave.)  But losing a few dB isn't as much
of a detriment as some might claim.  In fact, it isn't uncommon for a ham to
have that much loss in their antenna / feed system and not notice it, and they
sometimes even recommend such systems to others.

Remember also that above 20m the radiation pattern isn't optimum for DX for a
42' antenna due to the high angle lobes.  In practice you might only be down
a dB or two compared to a shorter wire, even on 10m, but that is an additional
consideration.

Good luck with your project!
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