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Antenna Stacking Test - ATF-X300

ATF-X300 Precision Antenna

shown with new style Integrated Stacking Boom

and Compact Vertical Tilter

Description:

The main goal I had when designing this new antenna was to build a smaller antenna that can match the performance of much larger and heavier antennas. I also wanted to design a new simpler stacking boom arrangement to save weight and reduce wind load. I must have tested a hundred different element positions during the initial development to find the optimum reception on all channels. 

 

I first tested each antenna separately. In all my previous tests I tested the single antenna mounted directly to the mast with its standard bracket. When tested in this configuration both antennas tested exactly the same. In this test, I placed the antennas on the stacking boom and ran a test on each antenna. I was surprised to see the difference in reception I got from just a four foot change in lateral position. I also found out that the optimum horizontal angle was different for each antenna. There was a 2-5 degree difference in horizontal angle, so I "toed in" the antennas about 5 degrees, this change gave me a 5% increase in signal.

 

I used a Spectrum Analyzer to check the waveform for each station. The waveforms allow you to measure signal strength in decibels and to see multipath interference in the signal. See below for results and comments.

 

Set up:

I mounted the antennas to my new Integrated Stacking Boom. The boom assembly was then mounted to a ATF-V100 Compact Vertical Tilter for precise positioning. Vertical angle positioning is very critical with stacked antennas, since the vertical beamwidth gets even tighter. The antennas were then connected to the Low-Loss RG-11 feed line through a Antenna Phasing Harness. I set the spacing to 48".

 

Results Definition:

  • XX-XX = Measured signal strength level

  • 0-XX-XX = Signal locks on briefly but keeps dropping out

  • 0-50 = Signal was detected but not able to lock

  • 0 = No signal detected

  • -- = Not tested

Note: Signal level refers to the Dish 6000 indicator which measures the signal quality based on percentage of errors. As long as the indicator stays above 48-50%, the signal will lock. I assume that if you have over 50% errors, the Dish 6000 does not have enough good signal to decode properly. A reading of 100% would indicate no errors in signal. I have found that at 47% I will see pixelation in the picture and below 46% the picture will drop out completely.

Dish 6000 Test

Spectrum Analyzer Waveforms:

Mt. Wilson Stations (15 mile distance)

Antenna A

Antenna B

Stacked A+B

48" spacing

atf-x300_test 002.jpg (60459 bytes)

Channel 31

atf-x300_test 011.jpg (60783 bytes)

Channel 31

atf-x300_test 020.jpg (60687 bytes)

Channel 31

atf-x300_test 003.jpg (60406 bytes)

Channel 36

atf-x300_test 012.jpg (60818 bytes)

Channel 36

atf-x300_test 021.jpg (61742 bytes)

Channel 36

atf-x300_test 004.jpg (60348 bytes)

Channel 42

atf-x300_test 013.jpg (60915 bytes)

Channel 42

atf-x300_test 022.jpg (61123 bytes)

Channel 42

atf-x300_test 005.jpg (59144 bytes)

Channel 53

atf-x300_test 014.jpg (60005 bytes)

Channel 53

atf-x300_test 023.jpg (62009 bytes)

Channel 53

atf-x300_test 006.jpg (59177 bytes)

Channel 59

atf-x300_test 015.jpg (60151 bytes)

Channel 59

atf-x300_test 024.jpg (62775 bytes)

Channel 59

atf-x300_test 007.jpg (61225 bytes)

Channel 60

atf-x300_test 016.jpg (61912 bytes)

Channel 60

atf-x300_test 025.jpg (63213 bytes)

Channel 60

atf-x300_test 008.jpg (60889 bytes)

Channel 61

atf-x300_test 017.jpg (62733 bytes)

Channel 61

atf-x300_test 026.jpg (63780 bytes)

Channel 61

atf-x300_test 009.jpg (61524 bytes)

Channel 65

atf-x300_test 018.jpg (62466 bytes)

Channel 65

atf-x300_test 027.jpg (64826 bytes)

Channel 65

atf-x300_test 010.jpg (61191 bytes)

Channel 66

atf-x300_test 019.jpg (63042 bytes)

Channel 66

atf-x300_test 028.jpg (63688 bytes)

Channel 66

 

Conclusion:

  • As noted above, in all my previous tests, I tested the single antennas mounted directly to the mast in the same lateral location. When I tested the X300 in identical locations, both antennas tested exactly the same with the waveforms appearing the same on each antenna. However, during this test, I placed the antennas on the stacking boom spaced 48" apart and ran a test on each antenna separately. I was surprised to see the difference in reception I got from just a four foot change in lateral position. At first I thought it was because one antenna was shielding the other, so I removed the antenna not being tested and found it was actually the change in lateral position that was accounting for the difference in performance. This is proof that the placement of your antenna on the roof plays a important part in reception, especially in multipath conditions!
  • It is easy to see the level of multipath in the pictures above by the sharp notches and bumps in the waveform. A nice, clean signal should appear as a straight horizontal line. I have found that the flatter this line gets, the higher the signal number gets on the Dish6000 and the better the channel stays locked in. When the notches are deep enough (about 7dB) the signal will not lock in. The stacked antenna arrangement greatly reduces the multipath notches in the signal.
  • Horizontal stacking decreases the vertical beamwidth, this makes the vertical angle of the antennas very important in locking in the weakest stations. Example- It would be very difficult to get channel 53 (ABC) without a vertical tilter. If I change the vertical position of the antenna just one degree either up or down, channel 53 will drop out completely. Fine tuning for strongest signal on 53 is just a matter of +/- 0.5 degree. With channels 36 and 65, the critical angle is +/- 2 degrees and channel 31 is +/- 3 degrees. This angle will change according to weather and time of day.
  • The horizontal tuning angle also decreases. For the weaker stations, just +/- 2 degrees makes a big difference. For the best signal I normally manually enter the angle on the Channel Master rotator, since it moves in 2 degree increments when you push the arrow buttons.
  • Not shown in this test is the reception from San Diego 130 miles away. When the atmospheric conditions are favorable, all San Diego channels come in very strong. Horizontal and vertical angles are not as critical when picking up long distance signals since multipath is rarely a problem, increasing gain yields the best performance with long range reception.
  • I have been running these two X300's now for about two months. They are so far the best performing antennas I have used to date. I can't tell you exactly why that is, since all my development was done through trial and error and not by using a computer program or a laboratory. I did use a spreadsheet for calculating the progressive element spacing. I was able to modify certain variables to alter the spacing characteristics, then I did tests to determine the values which seemed to work best. I then fine-tuned these variables to get the optimum performance.
 

  


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