I'm a bad article writer, lacking those skills and my English isn't that good to be so eloquent as most writers.
Still testing around, tried a T225-2 Amidon core in 1:9 and 1:4 unun, but the FT 240 - 43 core with 11 bifilar windings with Teflon coated silvered wire still gives the best results.( used in the Airbus planes)
Everyone can use the data and piccies provided in this thread to make something about it if he/she feels it is worth producing it for a club.
This was my "hunt" for a better vertical as the Imax 2000 is, starting point was it had to work well from 20 up to 10 meters, no traps wich add losses and complexity, sturdy to withstand 130+ mile storms, be of reasonable length, manageable on the roof on a concrete chimney, but that also would work on the ground.
That would add 17 and 20 meters to the vertical working better as the Imax 2000.
The choice for an 1:4 unun to keep the swr on the coax feed line low was easy picking, I have been experimenting with that before in my quest for the 160 meter antenna a few years back I wrote about here.
Since I had a lot of titanex tubing around and the Imax top sections as spare I could change the lengths of the vertical from 21 to 31 feet and xperiment here on the ground ( 6 foot off the ground with raised radials) with the effect of the length and bandwith and effect of radiation pattern of the vertical.
I was not trying to re invent the wheel, there is a lot of stuff written about this on the net as I found out in the process, my initial database I referred to was Low band Dxing from ON4UN, the RSGB and ARRL antenna books, as well my own experiences in building verticals over the years.
In my first tests the 31 foot vertical was easy tunable from 40 -6 meters, with the FT 240 -43 core 70 MHz ( we have a band there here) and even 2 meter had usable dips, but the radiation pattern there will be quite weird to say the least.
Since I still have the working Imax 2000 with ground radials on the roof at 35 feet and top on 55 feet over the ground I can compare the vertical with the Imax 2000 with a flip of the Heathkit antenna switch.
The Imax is fed with 50 feet of a LMR400 comparable coax, low loss, the homebrew vertical is fed by 100 foot of RG58U that has about 3dB loss.
So, being higher up, free from the ground clutter and low loss coax compared to a ground mounted between the houses vertical with 3dB loss coax on it.....;)
The Imax is fed with a wideband circuit you can find on the net, andf has a 23 foot radiating element encased in the glass fiber parts.
The radiator of the imax is capacitive coupled and prone to static noise.
The 1:4 unun in the 25 foot new antennas connects the radiator to ground electrically, but I will add 180KOhm resistor of pressed carbon 5 watts over the radiator and ground connection as "just to be sure".
With 11 bifilar windings on the FT 240 - 43 core the 1:4 unun is working fine from 160 meter - 50 MHz as the MFJ 269 alayser showed in tests.
XL at 1.850 is 1.308 KOhm, on 80 already 2.545 KOhm, 7.1 MHz is 5.1 KOhm, 14 MHz is 9.686 KOhm, running up to 29 MHz 20.5 KOhm, 50 MHz is 35.5 KOhm.
These values need to be on the safe side 5 x as high as the feeder impedance, here 50 Ohm.
A T200-2 core needs too much windings, introducing large capacitance over the windings and more then halving the effective signal.
It is ferrite, no iron core, handles 400 watts on 7 to 30 MHz as I tried without the core heating up too much, on 7 MHz the core went luke warm with 400 watts carrier for 10 minutes.
You can for more power glue 2 cores together and lower the windings to 9 or 10 bifilar windings.
The 1:1 choke is also made of an FT 240-43 core with 2 x 5 windings of 50 Ohm coax on it after 5 windings cross over to the other side.
With 2 x 11 windings bifilar the inductance is 112.5 Micro Henry.
The Amidon powdered iron cores handle more power, but need double the windings to get anywhere near a working solution.
Even then the results showed the FT 240 - 43 core to be much more efficient in this contraption.
As choke it is actually quite ideal, one core with 2 x 5 windings will do legal limit but just...
Here 5 mm Teflon coax was used but loose winding RG 58U will work as well, though it will not stand heat as well as Teflon coax.
Cover the FT 240 - 43 cores with glass fiber tape the do conduct and the tape will protect your windings against sharp edges and isolate the core.
Chosing 25 feet is done to keep the length of the antenna as far as possible away from any resonant point on 7 - 29 MHz, be it 1/4 or 1/2 wave or even 5/8 wave.
Next post a few piccies of the 1:4 unun with FT 240 - 43 core Teflon wire and end result antenna.
Alternative feeding is with ladder line to the shack and use a tuner directly or balun and few feet of coax depending on the tuner you have.
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Originally Posted by PA5COR
