Antenna Evaluations

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I know this is somewhat off topic, and I don't want to start a big debate, but some of you contesting and DX antenna experts might give me some practical advice...

I just discovered that it is going to be much more expensive to do my antenna system the way I had thought - with a homemade Hazer on Rohn 45G, freestanding at 55 ft. with the T-11 Log Periodic at 58 ft....

It looks like I might  not be able to do the Hazer.  I cannot guy the antenna so I am thinking of putting it on 35 ft. of 45G with 3 ft of mast above the tower, which should be OK except for 100 MPH winds, which would give me more important things to worry about than saving my antenna.

So here is the question.... What DX performance would I be losing with the antenna only at about 38 ft. instead of 58 ft?

I know that all the books say that best performance is at 1 wavelength high which is usually stated as about 65 ft for 20 meters.  But what is going to be my real-world sacrifice?

In any case it will be the best antenna I have ever had in 41 years.  
But I will also be sacrificing some height on hanging my dipoles for 40/80 and my inverted 'L' on 160...

What say you all?
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Ken - NM9P, Elmer

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  • a bit frustrated...

Posted 4 years ago

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Walt - KZ1F

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I covered this before Ken but price out a TX-455, M2-10-3LP7-125 (ruggedized version of the T7. If the antenna was up a little off the top of the tower (55' in the TX-455 case) the hit off of 1 wavelength would be negligible. One thing, however you might want to consider is your HAAT. When I was studying for the exams I took HAAT to be height above trees and hills and sides of building etc, say within 1/8 - 1/4 of a mile. Not so, FCC has a webapp and even though I am at the tallest point for miles in any direction my HAAT is in negative territory as a few miles from here there is a hill 500' above my elevation. That's just one direction. There may be others in the other 3 directions (or 7 depending on your compass rose. One reason I did not go with the Steppir or more directional higher gain antennas is I read where a very high gain antenna in a low HAAT situation actually is detrimental. The T-7 being a little less gain would radiate better in my situation as less energy directed into the side of a hill. As far as at 38', It's all in the radiator. If you lost 2db (about 1/2 an S unit) that is nothing a linear couldn't compensate for. Do you have access to an ARRL antenna guide? Oh, if you don't have icing and/or wind issues ruggedized may add no value for you. In the northeast we get ice, in Virginia, we got ice. My KLM KT34XA would be like a shiny metallic upside down U in February. Last month, my LP was perfectly parallel to the ground. Oh, LP..you have a FLEX right? Or do you actually own the T-11 vs that's your working choice for a yet to be purchased antenna) You may or may not be at the point of not doing a lot of tower climbing but that's an issue as well. For 20m with a 10-30LP, I use a KAT-500 external ATU. Works pretty good I've pushed 600W through it.

Walt
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Ken - NM9P, Elmer

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Thanks, Walt,
I already own the Tower, T-11 (Still in the box) , rotor, coax, lightning arresters, rotor cable, ground rods, etc. 

10 ft. of the 45G is already in the ground (5 ft. of it is out of the concrete), it is mounted in a 5 x 5 x 5.5 ft concrete base.  The base was installed last May, then life happened and the rest of the project got postponed until after winter.  Now it is tower season again in SW Indiana.

Rohn's specs say the 45G can be used as a self-supporting antenna with 9.8 sq. ft. at 35 ft. and wind loads of 90 mph.  Taking into account their CYA factor and the fact that we seldom get winds that high, except for the occasional tornado, I am figuring that I could do OK with the T-11 antenna 3 ft above the tower and a 2 meter 10x10 yagi 6 ft. above that. and still be safe.  (speaking from memory, I am not at the computer with the exact data. 

I cannot guy the tower unless I put a large I-beam on the other side of the driveway so that my van could drive under it.  The property line only extends a couple of feet past the side of the driveway.  If I could be sure that the I-beam approach would be an acceptable guy on that side of the tower, I would put up 55 ft of the 45G and go for as a guyed tower.  Phillystran is not that expensive compared to the rest of my station.  I would only need one set of guys at that height, attached about 80-85% up from the base.

As far as Ice, we seldom get more than 1/4 inch here, and even that only every few years.

I bought the tower used, in good shape.  I got a total of 85 ft.  (one tapered top section, seven to ft. sections, one 5 ft section, and all of the guy braces and arms, rotor plate, and large turn buckles.  I have about $850 in the tower, plus I bought new bolts for 5 sections.

I have thought about shifting the project to a certified 50-55 self supporting tower, but I am not confident that cutting off the Rohn and drilling the base and installing a different tower in the base using some sort of concrete epoxy or other adhesive (as another ham suggested) would meet good engineering standards.  Besides, I made my decision when I bought the Flex-6500 that I would save my $$ for a larger and more expensive tower until I retired in 7-10 years and moved to a permanent home in retirement.  My current home is a parsonage provided by the church that I pastor and the Trustees are kind enough to let me install a moderate tower.

If I had my "Dream Tower" I would be looking at a Heights fold-over with the electric screw mechanism and putting up about 65 ft of it.  They are awesome towers, but you pay dearly for them.  

Ken - NM9P
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Doug Hall

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Ken,

About 10 years ago I was asked almost the very same question by a friend in Salem, VA. He had planned on a 60 ft tower but guying issues made that impractical. He already had a Tennadyne T8 in the box. I put his antenna up 40 feet and he was delighted with the performance. That setup has survived high winds and ice buildup that took down lots of trees in the neighborhood. The tower is still standing and the T8 looks nearly as good as new.

My experience (I'm not a tower professional but I've been climbing and doing tower work for nearly 40 years) is that Rohn's specifications are pretty conservative. I think your plan to use the 45G unguyed is sound, will save you money, and will yield an antenna setup that you'll be pleased with.

73,
Doug K4DSP
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W5XZ - dan

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the penalty will be greater on the lower freq's, ken. (of course)..70' was always magic for 
me, in the past; high enough for a 40m 'shorty forty', good results 20m & up...you sure save
a BUNCH if you commit to guys, ya know...73
(Edited)
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KY6LA - Howard, Elmer

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@Ken

I strongly suggest that you run HFTA for the different bands and different heights before you make any final decisions...

In many terrain situations I have found that lowering the antenna can result in better propagation.

For EXAMPLE at the NX6T contest Station which sits on top of a 950' hill, we found from both HFTA and Contest Results that 20M Propagation to Europe was much better at 45' than at 70' 

So your terrain can make a huge difference.. OTOH you are in Indiana -- IIRC it's pretty flat?
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Ken - NM9P, Elmer

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Indiana is pretty flat in many areas, but we have som hills in southern Indiana. Here it is more like gently rolling hills, but Washington, Indiana is in the river bottoms.

I will look up HFTA. I am not that familiar with it.

Regarding height, I want to be safe, but not paranoid by what can sometimes be manufacturer's overly conservative specs done in the name of CYA, rather than actual engineering. I am not sure how much "fudge factor" Rohn includes in its specs. I would hope that someone here would shout a warning if I am going dangerously high here, or encourage me to go another section higher if I can safely do it.

Ken - NM9P
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W5XZ - dan

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maybe a couple sticks of 55 at the bottom would help?  my last tower, back in the 80's, was all rohn 55; VERY sturdy; ought to be, at 100# / section! JM2C..
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KY6LA - Howard, Elmer

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@Ken

Stu K6TU has an excellent HFTA Based Propagation Service . It will give you the terrain maps for free (that is the hardest part)

If you send my your terrain maps from K6TU, I can run HFTA with various options for you.   Or you can just play with the ones Stu does which are also excellent...

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DrTeeth

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OT: did you see the story of the JA ham with a full sized 3-ele beam for top band?
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KY6LA - Howard, Elmer

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His is bigger than Mine?
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Ken - NM9P, Elmer

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I must think that an array of four good verticals would be as effective and less expensive to engineer at any height that would be effective for DX on 160? But I would LOVE to see it!
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Rob Fissel

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For your viewing please ( I couldn't find the JA one, but I've seen it as well):

https://www.youtube.com/watch?v=XCZcjqltJVA
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KY6LA - Howard, Elmer

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IIRC that is the Radio Arcala Tower that collapsed in the snow and ice

http://www.arrl.org/news/storm-takes-down-amateur-radio-contest-club-towers-in-northern-europe
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Jon - KF2E

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Ken,

I have a three element SteppIR at 32'. It is there because I didn't want to fight with the zoning. I have been delighted with it's performance. It even performs well as a dipole on 40m. Antenna work is all about compromises. Do the best you can and I'm sure you will be amazed at the increase in performance over your wire antennas. I doubt the difference you will see at 38' will be significant.

Jon...kf2e
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KY6LA - Howard, Elmer

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Ken

I have a SteppIR as well.. I have always found that LPA were a compromise at best...

But clearly better than a dipole...
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Ken - NM9P, Elmer

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Yeah, I figure at 5.8 dBd I am losing a little gain in return for lower maintenence and broadbanded response all the way to six meters. This isn't my dream antenna system. I wanted my dream rig first, given my current location.
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Walt - KZ1F

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I was told my LPA was effectively a 3 element mono on 4 bands 17-10. That was one of the decisions I made due to knowing I was getting a flex, and again, the HAAT would actually hurt a 4 or 5 element mono. Howard, being almost at sea level, you have a what, +80' HAAT?
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KY6LA - Howard, Elmer

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Walt

Not so Simple

I am on the side of a mountain...

So I am likely about -400' BELOW AVERAGE Terrain to the East and North

However I am 680' HAAT to the Pacific

My site is perfect for a JIDX Contest or an Asia Pacific Contest as I can usually run 30 minutes longer openings on any band than the rest of the NA Stations in those directions...

My SteppIR MonstIR is 10+ years in the air.. Only real maintenance was once to paint it for UV Marine Paint and once to repair an element because I was remote when I rotated it into a 6M Vertical's Guy Wires and did not look at the camera to see that I had not been raised...

I would take a SteppIR over ANY LPA any day as it is a true monobander at all frequencies...
(Edited)
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Steve Gw0gei

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Ken, I used to run a T8 on a 35ft slimline wind up mast as a mult antenna in my previous contest qth on Anglesey Isle, North Wales. I found it was a great antenna for mult hunting and with the antenna sat at 40ft on top of a stub mast it worked well on 20m into usa/ve and to vk/zl.  I had a th7 and then a 204ba monobander on a 60ft lattice wind up tower as my run antenna and there was never much difference if any between them at 60ft and the t8 at 40ft.

73

Steve gw0gei

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Charles - K5UA

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Hi Ken,
Do not succumb to paraylsis by analysis (as I am often guilty of). Get the LP up at the height you can maintain, afford, and feel comfortable with. Remember, perfection is the enemy of good. You are bleeding fun every day that antenna sits In a box instead of radiating on top your 35 foot tower. On 20 meters you will have a nice single lobe with no high angle radiation. It will amaze you compared to your wire antenna. If I am not mistaken, you are a pastor...... live for today, tomorrow is promised to no one.
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Paul Christensen, W9AC, Elmer

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Recently, N4CC and I went through the exercise of analyzing our compromises.  For 30m-through 10m, we ended up with a Tennadyne T14-HD on a 42 ft boom.  On 40m, we have a M2, full size  4L monobander.

Due to the design of an LPDA, forward gain is mostly consistent across the designed frequency coverage.  In the case of the T14, it is 8.5 dBd.  F/B varies as a function of frequency between 15-25 dB. 

By contrast, the SteppiR MonstIR's gain varies with frequency.  In terms of forward gain, the T14 wins on 30m-20m.  A toss up on 17m, and the MonstIR is slightly better from 15-10m.  In terms of F/B, the MonstIR  12dB -24 dB but SteppIR's metric is F/R not F/B so it's a bit of an apples to oranges comparison.

Both antennas have 42 ft booms.  The MonstIR weighs 90 lbs. more than the T14 and here in FL, is more susceptible to lightning-induced failure than the T14.  Price difference?  About 3X more for the MonstIR.

Now, the MonstIR does have 40m coverage so, in that respect, it's an unfair comparison between types.  If we had only one tower, we probably would have reconsidered the MonstIR, but we are fortunate to have a separate 140 ft tower just for the 40m monobander.

The comparison gets even more interesting with the SteppIR 4L that covers 20m-10m (with optional 30m).  The gain of the T14 is again better 20m-15m. and about even gain above that to 10m  On 30m with the SteppIR add-on kit, the T14 will blow the SteppiR away.  The T14 weighs 45 lbs more than the SteppIR 4L but costs a few hundred $$$ less..

So, lots to consider in the game of compromises.  The SteppIR models have the cool ability to quickly reverse direction that a LPDA cannot do.  

Finally, I do not consider a SteppIR any more of a "monobander" than a LPDA.  If the element spacing was part of the SteppIR design, then we would get much closer to "multi-monoband" performance.  When you look at gain and F/R ratios across bands of the SteppIR models, it's clear of the compromise made and that they do not have multi-monoband performance.  An antenna like a Force12 C3 fits that description much better.

Paul, W9AC


(Edited)
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Stan - VA7NF

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Ken, start with the shorter length but be sure to spread fertilizer and iron pellets around the base.  Water well and you will find your tower grows a 10' section per year without being noticed by the neighbours or parish.  73 - Stan 
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Ken - NM9P, Elmer

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Board of zoning appeals has already approved my antenna up to 70', including any vertical two meter of other antennas on top of the beam.  My snag is the hardware...I have already purchased the 45G and already have the first 5 feet in the concrete.....

If I could figure out a way to guy it safely with a guy going over the driveway high enough to drive my van under, then I would put up about 65 feet of the 45G.  But the left edge of my driveway is about 18 inches from the property line.  I would need to use a steel I-beam or large pipe and attach a guy to that.  I don't think I want to go to all that trouble engineering such an arrangement , getting it approved by the trustees (and perhaps even the zoning board, who approved the height based upon the concept of either guying the tower, or lowering the antenna with a Hazer when the winds came up.)

So it is starting to look like I will just enjoy a great antenna at 38 feet.

Ken - NM9P
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Charles - K5UA

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Hi Ken,

Here are the plots for a typical 20M antenna, a 2 element quad, at 38 feet and 58 feet high.

As I mentioned, the az plots are at the same angle as the angle of maximum radiation, commonly known as the take off angle.  I also included the 3D plots to give you a visual reference of the solid geometry of a radiation pattern from a typical antenna.  I did not have a model of your LP in EZNEC, so the gain figures will be different, but the differentials should be about the same as the plots of this 2 element quad.

It is interesting to note the energy distribution in the forward lobes of the two different heights.  The lower antenna should be less sensitive to high angle signals than the higher antenna.  The gain differential between the two heights in minimal, but the lower lobe of the higher antenna will give it a slight edge in the lower angles that more useful for DX work.

Hope to see you on the air with the new antenna soon.












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Ken - NM9P, Elmer

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Thanks! It almost looks like I would receive less interference from stations close in while working DX... With perhaps 2-3 dB loss at lower angles. Not too bad.
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Charles - K5UA

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That is correct Ken. That lobe at 55 degrees on the 58 foot high antenna would be responding to high angle domestic signals which would be suppressed by the pattern of the 38 foot high antenna, at the expense, of course, a higher overall take off angle and less energy at the extremely low angles. Also, the front to rear of the lower antenna is better than the higher antenna. This means the signal to noise ratio of what you want to hear off the front of the lower antenna will be slightly better than the higher antenna in the receive mode.

All in all, what you give up by installing the lower antenna instead of the higher antenna is so insignificant compared to what you are giving up by leaving the LP in the box and continuing to use the wire antennas.
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Bill N5TU

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This is a reply to Paul, W9AC.  The MonstIR was quite the antenna, but it has been out of production for many years.  (Yes, Howard, KY6LA, has one ...)  The choices for the replacements in that size range are the DB36 and the DB42.  These are also expensive and massive; wind-induced torque seems to be the main problem with these.  (No, I am not an engineer, I am a classical musician, so I am reporting what I read elsewhere.)  NN4ZZ has dealt with these issues, so perhaps he can comment.

At any rate, those are my $0.02 worth.

VY 73,
Bill, N5TU
(Smaller SteppIR going up soon)
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Paul Christensen, W9AC, Elmer

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Bill,

I stand corrected.  The data I referred to above is for the DB42 model, thinking it was essentially the same as the MonstIR.  So, replace that term above with DB42 and hopefully it makes more sense.  Thanks for bringing this to my attention!

Paul, W9AC 


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KY6LA - Howard, Elmer

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My MonstIR only has a 34' boom... vs the 42' boom of the DB-42

But my Elements are 70' vs the much shorter DB-42 trombones
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Al / NN4ZZ

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Hi Bill,
Yes the DB36 and DB42 initially had issues with excessive lateral boom flexing.  The weight and wind load on these big antenna was too much for original boom truss setup.  The original boom truss support and cables only provided vertical support for the boom.  We solved for the TiltPlate by offering an optional lateral support strut.  Later SteppIR came out with an improved boom truss support with a T-Bar on top that solved the problem.  

The new T-Bar boom truss is standard on the DB42 and offered as an option on the DB36.  You can also get a retrofit kit for the older MonstIR antenna.  

More details on the issue, solutions,  and pictures on my web page at:

http://www.nn4zz.com/Lateral%20Strut%20Mount.htm

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com


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KY6LA - Howard, Elmer

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Wind induced torque, Wind Area and Weight are NOT such a big issue if you use intelligent engineering practices.

My MonstIR sits on top of a US Tower MA-850MDP Motorized Tower with a Rotor Base.

Torque:  My MonstIR with  3 - 70' Elements and 1 -35' Element has a very large turning moment.  Yet I have successfully used a Yaesu GX-2800 instead of something like a huge prop pitch motor to turn it for years with no issues whatsoever.  How?  I did not use a tower mounted rotor which is subject to turning stresses but rather I used a turning base to rotate the entire tower.  The rotor base completely eliminates the bending stress on the rotor and adds inertia so that wind moment is reduced. I chose the GX-2800 because it had the Largest Braking Force of any rotor on the market as it is more than capable of holding the MonstIR from moving at 70MPH design speed.

Wind Area:  My MonstIR is rated at 23.9 Sq FT.  My US Tower MA-850MDP is rated at 6.4 Sq Ft at 85' @70 MPH...  I installed a Wind Alarm on the tower to measure wind speed at the top of the tower.  I built an automatic tower retraction system that automatically retracts the tower when the wind speed exceeds 25MPH.   In fact the MA-850 is rated at 24 Sq Ft  @85' at 45 MPH and 24 Sq Ft @58' @70MPH... one just needs to understand the physics of towers at different heights and use the numbers intelligently to have a safe installation.  This only works for motorized retractable towers.  (yes I have backup power for the motors)

Weight:  Mostly effects two numbers - the overturning moment and the lifting motor cable. To counter the overturning moment, I upgraded the tower base design from a 6 Cu Ft of concrete to 10 Cu Ft of Concrete.  To counter the lifting cable stress, I upgraded the cable and hardware from 1/4' Steel to 3/8" Stainless - yes the stainless was not as strong as a 3/8" steel but I live by the ocean where salt in the air destroys ordinary steel..


Basically - intelligent design solves a lot of issues.


Performance...My MonstIR rocks... I regularly am the first to work DX on the Pacific Rim.   The almost instant reversing of the antenna is a major advantage during contesting.  To be working South Americans and then almost instantly Japan at full gain really boosts Q rates.

We currently have a Force 12 C31 at the NX6T Contest Station in addition to the SteppIR's.  Several of us are not particularly impressed with that Yagi compared to the SteppIR's at the site.   Over the years we have had LPA at NX6T but i have always found them to be poor seconds to the SteppIR's   I don't think we have had a Teledyne.


BTW - One of the things I really love about the SteppIR's is their close to 1:1 SWR everywhere.. totally eliminates the need for a turner...or even the ATU in the radio...
(Edited)
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Jon - KF2E

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Howard,

I hope you meant cubic yards of concrete. If it was 10 cubic feet your neighbor better watch out.

Jon...kf2e
(Edited)
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KY6LA - Howard, Elmer

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Yup Yards... Actually it turned out to be closer 12 yards to fill the hole.  - So much for real world vs calculations
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Ken - NM9P, Elmer

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Thank you, everyone who weighed in on my antenna project, both here and those with whom I have talked via private emails. I have decided to yield to my "need for sleeping well" with the antenna on the 35 ft. tower. It will be simpler than messing with winching a hazer up every time I want to operate. The T-11 is a very strong antenna physically, and is very low maintenance if installed well (I already have the Penetrox, and the tape and plugs for the element holes, too.) Current plans call for using Wireman's Ultraflex, LMR-400 equivalent for the LP and the 2 meter antennas, breaking the coax at the base of the tower for lightning arresters at the ground stakes there, and then running about 85 ft and in through a window panel at the shack (spare bedroom) window. I will have another ground outside the window running to a ground bus at the ham desk just inside the window. I will eventually be moving to an AGM battery charged by my AC supply and will slowly implement Howards advice re:eliminating as many wall warts and switching supplies in the house as possible by using analog supplies and power busses to the routers, switches, roku boxes, chargers, etc. I will be keeping my vertical and removing the 10 & 20 meter side elements and trying a 3o meter side element made from wire. the Dipole in the tree may become a dual band parallel inverted 'L' for 160/80, which will also load nicely on 40 meters. Add my homebrew tuned receiving loop for 160/80 meters and I will just about be set.

Thanks again everyone. Your comments and advice were very helpful in helping me be at peace with my decision.

Ken - NM9P
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Bill N5TU

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Enjoy it!  :-)

VY 73,
Bill, N5TU
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Dan -- KC4GO

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Now I'll comment -- Remember getting there is haft the fun. When we go on our RV trips I spend lots of time planning. (even though I wander off course)
So enjoy... I had an AEA Kt34XA up at 70ft on Rohn 25 for about 15 years her in Florida 2 sets of guys going to I-Beam risers for the guys this was do to a small lot. It came down during hurricane Charlie when a neighbors lawn furniture warped itself around the tower and violated the wind load. 
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Paul Christensen, W9AC, Elmer

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Ken,

Using K5UA's antenna heights of 38 ft. and 58 ft., I created a set of terrain radial profiles based on a 3L Yagi placed in your back yard.  Google Earth was used to get LAT/LONG.   This information was uploaded to K6TU's automated terrain profile generator.  The result is a set of terrain profiles spaced every 1 degree between 0-359 degs. This result is then exported to HFTA software.

Two predicted performance graphs are presented.  The first depicts performance at 38 ft above ground.  The second is a prediction of performance at 58 ft. above ground.  Notice that based on natural changes in terrain, EM waves will constructively or destructively add and often over-shadow changes in height alone.    Because of this, the vertical profile graphs for elevated horizontally-polarized antennas as shown in the ARRL Antenna Book and other similar resources, should be viewed with this in mind.

Each chart shows predicted performance over the following terrain radials:

1) 45 degs. (EU)

2) 180 degs. (SA)

3) 330 degs. (JA)

4) FLAT profile in dark blue.  This is the predicted performance if the surrounding terrain was perfectly contoured in all directions out to 14,400 ft. 

The lavender colored bars show statistical arrival angle from EU only in this set of graphs.  The last graph shows the actual geographical terrain profile along each given bearing. Notice that toward EU, you have a big hill about 1 mile away.

Paul, W9AC

The graph below shows a 3L Yagi at 38 ft above ground.


The graph below shows a 3L Yagi at 58 ft above ground.

    

Geographical terrain profiles for all three bearings below:


(Edited)
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Ken - NM9P, Elmer

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Thanks.
If I read this riht, it looks like there is some difference, but nothing drastic.

BTW, if you got my coordinates from Google Earth or maps, they have my house mis-labeled. I am actually about three houses to the east.... The one with the concrete drive and a little pontoon boat pictured in the drive.

The tower is in the backyard, about even with the line of the end of the. house, and about 15 feet back.

I don't know if this would change the calculations much.....
(Edited)
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KY6LA - Howard, Elmer

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It usually needs to move about 50' for the numbers start to get different

BTW...Paul did a great job for you.... You have a big hill to 45 degrees .(Eurpoe?)..but other than that it looks like 38' vs 58' wont make a huge difference...

So you can sleep well with 38'

BTW.. tonite is my DX Dream Nite... 7 hour planned power outage in my entire neighborhood... Batteries are all charged, generators are fueled..All system are tested and ready to go from pure DC


I expect that there will be NO RFI tonite...