The KK4TR/KN4LF ALL-BAND TRANSMIT/RECEIVE "L" ANTENNA


THE KK4TR/KN4LF ALL BAND 160-10 METER "L" ANTENNA & THE CLIPPERTON "L" AMPLIFIER MODIFICATION. SEE DETAILS BELOW.
WITH THIS ANTENNA AND 100-125 WATTS I HAVE WORKED 48 STATES AND 46 COUNTRIES INCLUDING AUSTRALIA, ON 160 METERS IN TWO DX SEASONS. ON 17 METERS I HAVE WORKED ALL 50 STATES AND 107 COUNTRIES, IN ONE DX SEASON. KK4TR HAS WORKED 32 COUNTRIES INCLUDING AUSTRALIA, IN 2 MONTHS ON 160 METERS. NOTE FOR SWL'S- THIS ANTENNA IN IT'S PRESENT FORM AND LENGTH, MAKES AN EXCELLENT RECEIVING ANTENNA ON THE LONGWAVE, MEDIUMWAVE AND SHORTWAVE BANDS. HOWEVER, IT'S LENGTH CAN BE SCALED DOWN WITHOUT COMPRIMISING RECEIVE PERFORMANCE. AVAILABLE IN NEAR FUTURE- Detailed Discussion & Plans For:

  1. KN4LF 160 Meter Indoor Receiving Loop
  2. KK4TR 2 Meter High Gain Beam
  3. 1.28 Wavelength Extended Double Zepp, 3 DBd Gain!
  4. Half Square Antenna, Phased Verticals With 4 DBd Gain!
  5. Broadband Coaxial L (Not Inverted) For 160 Meters, With Dimensions For 80-10 Meters

ALL-BAND "L" ANTENNA DISCUSSION & PLANS

 
  Let me start off by stating that KK4TR and I don't make 
a claim that we have invented a brand new concept in vertical
 antenna design, though some of the combined design aspects 
of the antenna may be unique! We have simply identified the 
basic inherent weaknesses of your average city lot 1/4 wave 
inverted L and have devised methods to overcome these 
weaknesses. This antenna design is not a rival to a 4 
square vertical array but will outperform your average 
backyard 1/4 wave inverted L or dipole by leaps and bounds.

KK4TR and I are not Electrical Engineers, just two voracious readers of every book on antenna theory and design that we can get our hands on, some 50 years old. As avid antenna experimenters, we have put 2 years of field experimentation into this antenna design! Along the way we have come to the conclusion that antenna theory is just that theory, concepts not yet completely proven by controlled scientific experiment and not to be taken as gospel! We have also concluded that alot of sound basic antenna theory and design has been lost to time and/or watered down, to the point that many Amateur Radio Operators are grossly misinformed about the basics.
To be certain, an Electrical Engineer may come along and try to poke holes in some of the following antenna theory and concepts but one thing that can't be disputed is that the antenna is a proven informer! The average city lot backyard 1/4 wave inverted L suffers from several inherent weaknesses, high vertically polarized local noise pickup, absorption and pattern distortion of radiated signal due to surrounding ground clutter, high capacitive coupling signal loss between the antenna and your average poorly conducting soil conditions and low radiation resistance, a measure of antenna efficiency, due to the typically short (25-50 ft) vertical radiating element section of a 1/4 wave inverted L. With much effort the near field transmitted signal losses can be reduced to a point that you improve antenna efficiency to around 50% but the average backyard location makes it impossible to overcome signal losses in the mid field (1000-2000 feet) on 160 meters and signal losses in the far field (around 52,000 feet)(fresnel zone) is out of reach for all Amateur Radio Operators.
The 160 meter linear loaded 1/2 wave L antenna places the highest current point at the top of the support structure gaining the following advantages. The elevated highest current point of the antenna is above the majority of the local vertically polarized noise field. At my QTH my 1/4 wave inverted L noise level was always S9 to +5 over. With my 258 foot 160 meter linear loaded halfwave L, the noise level has been reduced to S2-3. Of course the actual amount of noise reduction will vary from QTH to QTH. Another advantage of elevating the highest current point is, reduced to nearly eliminated radiated signal absorption and pattern distortion, away from omnidirectional. In a sense you can say that the highest current point is getting a better omidirectional look at the radio horizon.
Another advantage of elevating the highest current point, is the reduction of capacitive coupling signal loss between antenna and ground and gaining the advantage of laying down l ess ground radials. Logic dictates that placing distance between the highest current point of the antenna and ground, reduces the coupling losses. The agreed upon standard for number of ground radials for a vertical antenna is 120 1/4 waves but you see a rapidly diminishing point of return after 16-20 1/8 to 1/4 wave radials. An alternative to ground radials is an eleveated counterpoise, which will be covered further into the text.
Radiation resistance, which as stated earlier is a measure of transmitting antenna efficiency is obviously a very important variable, basically the higher value the better. A 1/4 wave inverted L with a vertical section of 50 feet, will have a very low radiation resistance, around 15 ohms (very inefficient), increasing to near a theoretical 36 ohms as you approach a vertical length of 1/4 wave. Take this 36 ohms of radiation resistance and couple it with a poor ground radial system and you still have a very inefficient signal radiator.
There are several methods that can be employed to increase radiation resistance and henceforth transmitting antenna efficiency, excluding the laying out of dozens of ground radials. One is to raise 4 ground radials into an above ground counterpoise system. Four 1/4 wave wires approximately 15 feet off the ground, can rival 120 1/4 wave radials on the ground, as far as transmitted antenna efficiency goes but not necessarily concerning absolute lowest radiation angle. Another is to lengthen the transmitting antenna. As mentioned earlier, in theory the radiation resistance measured at the end feedpoint of a 50 foot vertical section of an inverted L is around 15 0hms, a 1/4 wave linear loaded L is near 30 ohms, a 1/4 wave 36 ohms, a 3/8 wave 300 ohms and a 1/2 wave 1000 ohms, a very efficient figure indeed! Basically as you lengthen the radiating element the radiation resistance increases and it decreases as you shorten it, it also varies with the diameter of the radiator. Antenna input impedance varies according to where you feed it.
So that's it in a nutshell, the 160 meter 1/2 wave "L" overcomes all the inherent weaknesses of the average city lot backyard 1/4 wave inverted "L". Now let's discuss the benefits of using the 160 meter 1/2 wave "L" on 80 through 10 meters, as a multiband antenna. As the length of a transmitting antenna exeeds a fullwave on the operating frequency interesting things begin to happen. Gain starts to increase and the radiation moves inward towards the axis of the transmitting wire, versus the 90 degree broadside you see on a halfwave dipole. As the transmitting antenna continues to become even longer in comparison to the operating frequency, multiple lobes of radiation form on the wire in response to the numerous highest current points that exist. The following table lists by band the number of highest current points on the wire (1/2's), the increase in gain and the radiation angle with respect to the antenna wire axis, with 90 degrees being broadside to the wire and 0 degrees being off the ends.
258 Feet Long Sloping at a 45 degree Angle
    FREQ KC   #1/2 Waves   Gain(dbd)   Rad. Angl
  • 1845      1.01         0.0 @        90
  • 3888      2.14         0.5/1.9*     52
  • 7225      3.99         1.3/3.0 &    35
  • 10115     5.58         2.2         29
  • 14263     7.86         3.0         24
  • 18139     10.00        4.0         21
  • 21338     11.83       4.8         20
  • 24960     13.87        5.6         19
  • 28400     15.73       6.3         18
@- some slight increase in gain over a 1/4 wave. *- collinear antenna, 2 1/2 waves in phase. &- 4 1/2 waves in phase.
Using this antenna on 17 meters I have discovered that it is very user friendly antenna and with minimal time and effort I have been able to work many DX countries.
It is strongly recommended that a parallel network tuner be used to load up the L antenna, as in a sense the tuner is part of the antenna. Also as a tuner will see approximately 10,000 ohms of feedpoint impedance your average store bought T network tuner can't deal with such a high impedance. My tuner consists of one 250pf variable capacitor and a 28uh tapped inductor.

It is also recommended that the parallel network tuner be placed at the antenna end feedpoint, with a high quality run of Belden 9913/RG-8U or Belden 9258/RG-8X coax back to the radio shack. For 80 Through 10 Meter operation, it is recommended that you use 450/600 ohm ladderline from the antenna end feedpoint, to the parallel network tuner in the shack or as KK4TR and I do, forget a feedline altogether and bring the end of the antenna into the shack to the parallel network tuner. We realize that the no feedline concept is taboo in Amateur radio but it's a zero loss, highly efficient method that works very well. Attaching one 1/4 wave radial for 80 through 10 meters, to the ground side of the parallel network tuner and tuning the radials for maximum current with the MFJ-931 Artificial Ground removes 100% of any stray RFI in the shack to zero. I have found a minor amount of shack RFI on 30,12,10 meters using the 258 foot L but have gotten rid of it easily using the above mentioned method. 73 and GUD DX from KN4LF and KK4TR.
L.B. CEBIK, W4RNL says: "Joe, Tell the disbelievers that WWVH uses elevated-feed vertical dipoles--and has had a heck of a signal for many decades. As I noted, you antenna is a form of vertical dipole with horizontal extensions rather than true hats. Hence, it is as good as any other vertical--and against some based fed versions, possibly better. Your ground wires essentially ensure a good rf ground between your gear and the antenna--always a good thing, but not likely to intensify signals. Enjoy the bands. -73- LB, W4RNL"

Article written by KN4LF

THE CLIPPERTON "L" LINEAR AMPLIFIER MODIFICATION

     The Clipperton "L" Linear Amplifier modification is quite an easy and worthwhile task to undertake. For many years these amplifiers have been used very sucessflly by the amteur community on all ham bands 160 thru 10 meters. The most common complaint was that there was not alot of output on the 160 meter band or for that matter some of the other low frequency bands. There were several reasons for this:
  1. The tuned input circuit wasn't very well planned out. It worked quit well with the tube type rigs with their pi-network output circuits. They match the output impedence of the exciter with the input of the amplifier.
  2. With the introduction and popularity of the transistor final rigs all of this changed. Now the name of the game was 50 ohms or reduced output from the exciter. Simple solution was to put a small antenna tuner (MFJ 900, 901 series) or even have an exciter with an auto tuner placed between the exciter and the amplifier. This solved the mismatch problem but it becomes necessary to retuned when the frequency as changed. Power output from the amplifier increases to about 700 watts as opposed to the orginal 200-400 watts before placing the tuner inline.This should take care of the problem most would say but it still falls short of the design perameters 800-1000 watts output!

   After some investigation it appears that the tank circuit on the amplifier had been detuned at the factory by design. It was probably done so the unit could be type accepted by the FCC. When the amp was first designed and built the amateur community was sharing the 160 meter band with many other services. We had severe power limitations and operating restrictions. In some areas very low power other up to 500 watts depending on the time of day. It just wouldn't make good business sense to build a product that would put out 1KW and expect the FCC to say "ok go build it but don't use it on 160 meters at full output". That would be like putting a "fox in the chicken house". Simply put the circuit was detuned to conform wth the rules of the day.
   To fix the problem in the tank circuit I `tried many things but none of them seemed to work to my satisfaction. I finally tried the the simple approach and "It worked". I added a transmitting capacitor(door knob variety) in place of the original value at C-16 on switch S1B(which is at the bottom and left of the switch) and a transmitting cap at C-15( which is just above on the same side) on switch S1B. The first was for 160 meters and the second was for 80 meters. A smaller value will probably be just as good for the 160m value but that is all I had at the time. Both of these values cascade on 160m so instead of the original value you have increased the capacity of the circuit by a great deal.
With these capacitors installed the load control on both 80 and 160 meters worked to abot mid-scale. Before the modification the load control would be turned down to the extreme low end of the tuning range of the variable capacitor(Max Capacity). With these two modifications my output power went from 750 watts peak out to very near 1250 watts on the high voltage tap(SSB). This very close to the design parameters of four 572 B tubes in parallel. I hear "THE FELLAS IN THE BACKROOM" saying right now " Itīs too simple, I donīt believe it, He went about it all wrong, You need to add inductance not capacity". Well all I can say to the disbelievers is that it works come down to 160 meters and listen to me work the DX with the Clipperton "L" amp and the TS 850sat. Iīve included some photos and a hand drawn schematic to show the positioning of the parts. Any other questions just send me an email. Otherwise just have fun operating this piece or resurrected old gear.


Schmatic and Top View Of Amplifier



For further information about anything I have mentioned here please contact me at:
k4tr@bellsouth.net
or

K4TR Antenna Mfg and Sales

Article Written by K4TR



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