Horizontal Pattern Comparison Plots
Vertical Pattern Comparison Plots
Often antenna modelling does not tell the whole story. On the air reception tests allow one to best determine performance under the very varied forms of propagation that are experienced on six meters. To accomplish these tests, I carefully calibrated the R9000 S meter at 1/2 S-Unit points across the full range of S 0.5 (-128 dBm average) to +60/S9 (-36 dBm average) on five separate frequencies: 45.250, 46.170, 48.250, 49.750 and 50.100 mHz. This was required due to the skewed response of the distribution preamp used ( 6dB higher gain and 2.5 dB better noise figure at 45.25 mHz than on 50.100 mHz). The choice of this response is based upon the fact that there will be less limiting external noise contribution on 45.25 mHz due to antenna inefficiency there and the 50.100 preamp performance (and the best place to carefully control excess gain) is more than adequate. Click on the links below to see the results of on the air antenna comparisons. These will be updated as I collect more data.
The chart below shows the real world results
on the air signal measurements. After spending countless hours
between the antennas while recording the data, one thing became
clear: Space Diversity works extremely well using the present
separations! It works so well that it is almost impossible to
determine which antenna is best unless the signal source is relatively
close. There are times when the lower (and lesser gain) antenna
show improvement over the upper by 6 dB or more and vice versa.
suddenly the upper antenna may show 10 dB of gain over the lower.
It is rare to find an instant in time when both antennas recieve the
signal level. All very dynamic and changing constantly!
To depict the actual results in chart form is not easy. I have chosen a method that shows the range of minimum to maximum dB variation over a number of measurements as RED VERTICAL LINES. These represent the improvement of the upper 6M9KHW over the lower 6M1136 (negative values indicate that the lower antenna was better by the amount of dB shown). Within each red vertical line is a blue dot which depicts the MEDIAN value of the spread between minimum and maximum and all blue dots are connected together by a thin blue line in an effort to show a trend if there is one. In some cases, only a single measurement was taken and in these cases only a blue dot indicates the value (min-max not possible with a single measurement). Over time I will take more measurements and update the chart (see update date at the lower right of the chart). At the present time groundwave, tropo and E-Layer (including MS) and F-Layer propagation modes are all "lumped" together in the same chart. However, the different propagation modes are actually separated in a subtle way (multiple data for the same distance) so that in the future it will be easier to chart that particular mode separately should I decide to do so.
EME echo test data are used to determine the vertical antenna pattern and shown in the link below. All echo tests were accomplished at a power output level of 1.5 kW (24 kW ERP) or less. As more test data are added, a clear pattern should emerge allowing me to determine the most effecient vertical lobes. The latest update along with total datapoints is shown in the lower right of the chart. The first echo test was accomplished during moonset on 24 July 2001 with positive results. Probability % is the number of times echos were heard / the total number of tests near that particular elevation. The values are of little use until a significant number of tests are accomplished for each given Lunar elevation (the antenna is fixed on the horizon).
The reader is urged to use extreme caution when making decisions based on these data. It is presented for the sole purpose of sharing my findings. This is a very complex subject!
CHART OF ON THE AIR COMPARISON DATA
6M9KHW EME ECHO TESTS (Used to confirm
CLICK HERE FOR ORIGINAL NORTH ANTENNA & STATION DESCRIPTION (NOW OBSOLETE)
SOME OBSERVATIONS (based on test data and installation):
1- That old Telrex design (regardless of how it was accomplished many years prior) is going to be difficult to match considering boom length, gain, real world performance and survival under a relatively harsh climate. This thing is a heavy beast- a battleship! I am always the skeptic!
2- The lightweight 6M9KHW 50' boom yagi turns with no effort and I have noted very little overshoot using a simple and relatively inexpensive T2X tailtwister rotor (same rotor on Telrex 6M1136 and absolute MINIMUM requirement). Let the antenna come to a full stop and wait a bit before setting the brake. This big "floppy" antenna seems to take up much of the stopping moment of energy simply due to it's "flop". No data under high wind conditions YET but I'm expecting good news. I will be turning this monster into (or away from) the prevailing wind when away, just like I treat the 36' boom 6M1136- just to be safe and present the lowest profile to the wind.
3- Based upon concern expressed by others, I used loc-tite when installing the driven element shorting bars. These "others" have indicated the potential of the set screws loosening over time. A second set of locking (Allen) set screws is another alternative but if this method is used, the first set to go in must be shortened IN HALF! VSWR was PERFECT (after raising) on 50.100 after CENTERING the allen screws 10.5" away from the reference shown in the manual. Do check VSWR on the ground (it won't look great) prior to install. We tested VSWR on saw horses ~ 36" off the ground and saw 10-15% reflected power just to insure no major issues. I trust the M2 documentation on shorting bar adjustment. After the antenna was mounted we saw just a "flicker" of reflected power on a 100W Bird Slug with 100W foward power. Nice (and equal to what we saw on the 6M1136)! Don't try to optimize VSWR on the ground- it's almost impossible with an antenna of this size!
4- I am concerned about boom sag and recovery after heavy ice loading conditions. I pre-stressed the Dacron boom support prior to installation, using the RISER and even went so far as to water (weather) it for two days prior to installation. I like the idea of no metallic objects in close proximity to this high-Q antenna. At initial installation, both ends of this long boom antenna are pointing slightly upward to compensate for initial sag (the setting of the weave). As a precaution, I installed extra long STAINLESS STEEL turnbuckles at the mast to give me about 2" additional adjustment range. The initial installation MUST assume some boom sag and be tight near the open end. I heard the knots (snap) tighten as I pulled in initial slack during the pre-stress! At install, safety wire was used to prevent boom support turnbuckle drift as per the manual.
5- From a (on the air) performance perspective- it does the job well. However, it is almost twice the height of the existing 6M1136 and one would expect better low angle performance due to this factor alone. I will do some pattern tests at a latter date. It's noisey here! On July 24, 2001 I heard my 6m EME echos for the first time.
6- To raise the antenna we built a rope harness. Use the RISER and reduce the boom support rope stress on it so it's not bent! Non-slippable knots around the boom going through the "eyes" of the turnbuckles with the open end parallel to the length of the boom. Form an inverted "V" with the apex approximately 36" above the boom and tie it off so that a loop is available for tie to a gin pole "pull rope". Make sure that the angles of the sides of the rope, going through the "eyes" of the RISER turnbuckles are straight so that the turnbuckle eyes are NOT modifying their angle. All knots will be reachable by the person on the tower. Next, use TWO tag lines tied in close proximity to the harness knots on the boom then "fly" this kite! It takes FOUR people. One on the tower, one on the ground to initially raise this monster off the ground until at the full extension of their arms (then they run to a pre-tensioned gin pole pull rope) and two to hold the two tag lines and guide ("fly") this monster away from guy wires, etc. as it is being raised. The folks holding the two tag lines should be well away from the base of the tower, pulling in an outward direction and each having control of left/right boom drift. Learn to fly before too high. We "flew" this kite into place with 15-20 mph winds without bending a single element on my tower- guyed in three places! Life on a hilltop is never easy.
7- It's 28 July 2001. The 6M9KHW was installed on 6 July 2001 after several days of pre-stressing the Dacron rope boom support. Upon installation, both ends of the boom had a slight upward bend. A few days ago we had heavy rain after a relatively long dry session. Today is the first day I note that the boom appears to be level. Temperatures have varied between +7C - +34C since installation.
8- It's 23 Aug 2001. Today I notice a slight downward droop on the 6M9KHW for the first time which will be corrected tomorrow. This probably means that the slight upward bend at installation, 49 days ago, was inadequate and should have been more profound. Late summer here has been hot and dry.
9- OPERATION UNDER ICING CONDITIONS: On 29 November 2001 I experienced the first ice storm since the 6M9KHW was installed. I am estimating a coating of approximately 1/8" radial ice. Under these conditions, the 6M9KHW was useless showing an almost infinate VSWR and a measured receive reduction in excess of 15 dB. Fortunately, I had the 11 Element Telrex to use. The Telrex was NOT affected by the ice buildup in any way. I was very surprised to experience such severe degradation of the 6M9KHW under these conditions! A few hours later, when all the ice had melted, the 6M9KHW returned to normal.
10- SNOW STATIC COMPARISON: On 13 January 2002, during a period of heavy snow, I measured the background level of received precipitation static. The results were: The 11 Element Telrex measured no perceptable degradation and the 6M9KHW came out with a whopping 18.6 dB of noise over the 11 Element Telrex.
11- T2X Rotor failures!!! After eating up THREE T2X Tailtwister rotors it became obvious that a more rugged rotor was required. All three failures were related to the bearing indicator pot inside the rotor housing. In addition, one of the rotors also had motor problems. A C.A.T.S. RD1800 was installed as a replacement on 29 August 2003.
The stacked 17B2 two meter array with the
antenna at 123' AGL was removed in early June 2001 to make room for the
6M9KHW. It was equipped with a homebrew tower top amplifier and
with 7/8" LDF. This array was very effective for long haul tropo, MS
Es with the added benefit of substantial EME capability.
We "flew" the 6M9KHW to 110' with a rope
and two tag lines (shown to the left). Here, Dave (K1DAM) battles
a breeze to install the first U-bolts on the boom to mast
At this height the 50' long antenna looks small.
Dave is on the way down for a cold "Sam Adams" after a very
day. Many thanks to both Dave and his Dad Mick (W1JJM) for their
assistance on this project! Note the slight uptilt on both ends
the boom. On the left is the 11 Element Telrex located 100' North
and 53' lower (57' AGL) than the 6M9KHW. Both antennas are
depending upon propagation conditions.
This is what the South tower looks like in July 2001
This is a June 2003 close call by a hot air balloon!
CLICK HERE FOR K1SIX HOMEPAGE