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?
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?
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.
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.
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.
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.
At any rate, those are my $0.02 worth.
(Smaller SteppIR going up soon)
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...
Thanks again everyone. Your comments and advice were very helpful in helping me be at peace with my decision.
Ken - NM9P
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.
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: