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 36

Channel 42

Channel 53

Channel 59

N/A

Channel 60

Channel 61

Channel 65

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.