KLM KT36hyb Hybrid Yagi antenna.
Due to a strong wind storm in november2013 the director element of my KT34 had disappeared.
The idea to restore the 3band-mono-director (with all new M² straps) with 3 separate ones
switched at once a big lamp in my brain.
Purchasing an original director or an old kt34 was and still is out of practicity.
Otherway I had to throw all the tubes in the trash or selling them as spares.
Maybe getting another old KT34 @LOW_price would give more chances to get the hands on good quality tubes
The 3 elements yagi showed a very bad performance either OnAir and on MiniVna,
no directivity and in some cases worster than my DX88 GP antenna.
During the lowering of the mast I thought:what will happen if I put a mobile director ?
The easiest way was to assemble a 10mt director with plastic tubes holding the electrical wire
and hanging it with a rope ahead of the driven elements.
plus two more cords have been added to keep the director parallel to the driven element
|link to larger pic
gain differences between no dir (yellow box) and with 10mt dir (red box)
Anyway I have been able to carry the mods only because I had the remaining unused parts from the conversion
of the old KT34XA 6elem yagi as you can see and read in another KLM web page of my HowTo.
First of all the prolonging boom element then the new directors.
The 10mt director A came from the old kt34xa , the 15mt director has been assembled from the old 5th-3band director, leaving out all the capacitor tubes.
The new 20mt and later the 5th 10mt directors have been cut from new tubes.
All the mods and adjustements have been made possible by a tiltable mast called the POF_FALCONE
which was built by me to help in rising and lowering the antenna.
See here how it works
During the antenna modifying period, about 3 months, I have raised and lowered the antenna more than 50 times to bring it at about 5 meters from the ground level.
This height has proven reasonably good compromise for all the testings compared to the final height of 10meters above the roof.
Also the unbalanced weight of the whole antenna toward the front with the more hardware added has been balanced putting
into the rear part of the boom almost 7kg of counterweight.
The study of the KT3 yagi without the directors is shown below.
Even if the simulations showed good patterns, on air test showed bad performances of the 3elements yagi
versus my DX88 ground plane.
I started to add new directors at the canonichal spacing of 0.15L, but the results were not good.
Searching the WWW for more infos about the KLM kt3x antenna I found an article of Bill N6MW and his relative MMANA study.
Thanks to this mmana file and after a lot of tweaking I came to the conclusion shown below :
The big deal has been to find the best compromise in the spacings of the new elements to obtain the best band gains vs F/B.
The dimensions of the directors have been replicated to the original lenghts resulting from the previous measurements of the rebuilt M2 antenna.
The original KT34 has a very complex radiating system, many theoretical test have been calculated and transferred to the new antenna.
Every time I moved an element of just 1 centimeter all the patterns moved togheter.
Of course I could not come to any acceptable gain pattern without the MMANA file of Bill N6MW.
After a period of two months (march to may 2014) ON_AIR tests have showen very good performances on 20 and 15 meters bands.
The 10 meter band has not given same good impressions as the lower bands. More tests have to be carried.
In november 2014 after another wind storm and another lexan insulator rupture in the radiating cell (and its substitution)
and with the bad experiences on 10meter band with the 2 directors, whose performances have not given the expected results
I deciced to remove the 10b second director.
Also the elements spacing are slightly different in the 3 directors config compared to the 4 elements.
At once the directivity and gain on the 10mt band rised so far that the difference could be audible at the ears.
Front Gain and F\B ratio showed much more stronger with the single 10mt director.
Of course the whole 10meter performance could be much better with 2 directors, the big problem is moving up&down the yagi from the mast.
Therefore I decided to just remove the second director, which is a much easier solution for me.
Here follows a theoretical comparison table in dbi:
the values for my antenna are calculated at 10meters height, the other values are taken from their own manuals.
In almost two years of use of this hybrid klm yagi antenna, the results are that 20 and 15 meters work very very good
and 10mt still are not so strong in gain as I supposed it should be.
Again the big problem is moving such big antenna up and down the mast and having friends available to help in sending test signals .
The bandwidth on the three bands is very fine and no problem with the resulting SWR:
Further report on the performances of the KT36hybrid solution follow......
mar. dic.2014, gen-apr 2015