Horizontal vs. Vertical Stacking Test

Description:
I used two Blake
JBX21WB antennas. To confirm that the antennas were working properly and matched
in performance I tested each antenna separately first. I used a Spectrum
Analyzer to check the waveform for each station. The antennas were very closely
matched.
For horizontally
stacking I mounted the antennas to my
ATF-V100 Vertical Tilter
using a custom made boom assembly.
This boom assembly uses a fiberglass tube to prevent the boom from becoming a
active element in the antenna system. Each antenna mount clamps to the boom and
allows for easy adjustments to the spacing between antennas. I had already
determined in previous tests that 36-44" spacing worked best, so I used 40".
For vertically
stacking I simply mounted both antennas to a common mast. I tested a 32" and 17"
spacing.
See below for
results and my comments following the tests.
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.
**For easier
printing, click on image to bring up a separate page containing just results.
Test#1, Date: 03/03/02

Spectrum Analyzer Waveforms:
(click on image to enlarge)
Mt. Wilson Stations (15 mile distance)
|
Antenna A
|
Antenna B
|
Horizontal Stacked
36" spacing
|
Vertical Stacked
32" spacing
|
Vertical Stacked
17" spacing
|

Channel 31 |

Channel 31 |

Channel 31 |

Channel 31 |

Channel 31 |

Channel 36 |

Channel 36 |

Channel 36 |

Channel 36 |

Channel 36 |

Channel 42 |

Channel 42 |

Channel 42 |

Channel 42 |

Channel 42 |

Channel 53 |

Channel 53 |

Channel 53 |

Channel 53 |

Channel 53 |

Channel 59 |

Channel 59 |

Channel 59 |
N/A
|
N/A
|

Channel 60 |

Channel 60 |

Channel 60 |

Channel 60 |

Channel 60 |

Channel 61 |

Channel 61 |

Channel 61 |

Channel 61 |

Channel 61 |

Channel 65 |

Channel 65 |

Channel 65 |

Channel 65 |

Channel 65 |

Channel 66 |

Channel 66 |

Channel 66 |

Channel 66 |

Channel 66 |
Conclusion:
- The level of multipath can be seen in the waveform pictures. A clean
signal should have a square top with a straight or sloping line. The bumps in
this line drastically reduces the signal levels on the Dish6000'. I have found
that the flatter this line gets, the higher the signal numbers get and the
better the channel stays locked in.
- Channels 31 and 36 are my strongest stations. most every type of antenna
can pick these up. The real test is whether the difficult channels can be
tuned in and locked.
- Horizontal stacking resulted in a flatter signal waveform on all channels.
Horizontal stacking also makes the antenna much more directional. Turning the
horizontal rotator just 2-3 degrees in either direction makes a big difference
on the signal numbers and the shape of the waveform.
- Vertical stacking only seemed to increase the gain on some channels. The
waveform remained about the same shape as when using just one antenna. On some
channels, the multipath got even worse than a single antenna. The beamwidth
was similar to that of a single antenna based on wider rotator tuning angles.
- If multipath is a problem, horizontal stacking is the only way to go.
- If multipath is not a problem, vertical stacking can increase your gain on
weak channels.
|