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Antenna Stacking Test - JBX14WB

Description:

The main goal of this test is to find a smaller, lighter, and less expensive pair of antennas for horizontal stacking. Since you are picking up some extra gain from stacking, you can afford to lose a little gain on each antenna. I used two Blake JBX14WB antennas in this test. These antennas are very similar to the popular JBX21WB tested here, except they are shorter and have only 14 director elements. To confirm that the antennas were working properly and matched in performance, I first tested each antenna separately. I used a Spectrum Analyzer to check the waveform for each station. See below for results and comments.

 

Set up:

I mounted the antennas to a Dual Antenna Boom Assembly for easy spacing adjustments. 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 started with 24" spacing, then 36" and 44".

 

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.

Test#1


Spectrum Analyzer Waveforms:

Mt. Wilson Stations (15 mile distance)

Antenna A

Antenna B

Stacked A+B

24" spacing

Stacked A+B

36" spacing

Stacked A+B

44" spacing

jbx14wb 017.jpg (61193 bytes)

Channel 31

jbx14wb 025.jpg (61901 bytes)

Channel 31

jbx14wb_ab 001.jpg (63498 bytes)

Channel 31

jbx14wb_ab 008.jpg (63180 bytes)

Channel 31

jbx14wb_ab 017.jpg (64602 bytes)

Channel 31

jbx14wb 018.jpg (63234 bytes)

Channel 36

jbx14wb 026.jpg (64485 bytes)

Channel 36

jbx14wb_ab 002.jpg (63957 bytes)

Channel 36

jbx14wb_ab 009.jpg (61304 bytes)

Channel 36

jbx14wb_ab 018.jpg (64555 bytes)

Channel 36

jbx14wb 019.jpg (61550 bytes)

Channel 42

jbx14wb 027.jpg (62590 bytes)

Channel 42

jbx14wb_ab 003.jpg (63168 bytes)

Channel 42

jbx14wb_ab 010.jpg (63342 bytes)

Channel 42

jbx14wb_ab 019.jpg (62233 bytes)

Channel 42

jbx14wb 020.jpg (61845 bytes)

Channel 53

jbx14wb 028.jpg (61197 bytes)

Channel 53

N/A

 

Channel 53

jbx14wb_ab 011.jpg (61361 bytes)

Channel 53

jbx14wb_ab 020.jpg (65180 bytes)

Channel 53

N/A

 

Channel 59

N/A

 

Channel 59

N/A

 

Channel 59

N/A

 

Channel 59

N/A

 

Channel 59

jbx14wb 021.jpg (61734 bytes)

Channel 60

jbx14wb 029.jpg (61743 bytes)

Channel 60

jbx14wb_ab 004.jpg (62208 bytes)

Channel 60

jbx14wb_ab 012.jpg (62288 bytes)

Channel 60

jbx14wb_ab 022.jpg (65446 bytes)

Channel 60

jbx14wb 022.jpg (61418 bytes)

Channel 61

jbx14wb 030.jpg (62866 bytes)

Channel 61

jbx14wb_ab 005.jpg (61170 bytes)

Channel 61

jbx14wb_ab 013.jpg (63309 bytes)

Channel 61

jbx14wb_ab 023.jpg (64357 bytes)

Channel 61

jbx14wb 023.jpg (63565 bytes)

Channel 65

jbx14wb 031.jpg (62941 bytes)

Channel 65

jbx14wb_ab 006.jpg (62043 bytes)

Channel 65

jbx14wb_ab 015.jpg (61842 bytes)

Channel 65

jbx14wb_ab 024.jpg (65515 bytes)

Channel 65

jbx14wb 024.jpg (61578 bytes)

Channel 66

jbx14wb 032.jpg (62843 bytes)

Channel 66

jbx14wb_ab 007.jpg (63100 bytes)

Channel 66

jbx14wb_ab 016.jpg (63532 bytes)

Channel 66

jbx14wb_ab 025.jpg (65560 bytes)

Channel 66


Conclusion:

  • I found the shape of the JBX14WB waveforms to be very similar to the JBX21WB, the main difference being the gain. The level of gain can be seen in the height of the signal waveform, the large graduation lines represent 10dB. This decrease in gain is to be expected, since the 14 element antenna has less gain than the 21 element.
  • Multipath reduction improves as the antennas are moved farther apart. You can see the level of multipath in the waveform pictures. Channel 42 is a good example to see how the signal line gets flatter as the spacing increases. A clean signal should appear as a straight 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.
  • The wider spacing resulted in greater multipath reduction, but it also makes the antenna more directional. Turning the horizontal rotator just 2 degrees in either direction makes a big difference on the signal numbers and the shape of the waveform, especially on the weakest channels, the stronger channels are not as sensitive. Going beyond 44" spacing, the tuning gets too sensitive, just the wind shaking the antenna around can cause drop outs on weak channels. It is best to experiment with the spacing in your location, but generally you can get away with wider spacing the farther away you are from the transmitters.
  • Horizontal stacking also decreases the vertical beamwidth, this makes the vertical angle of the antennas very important in locking in the weakest stations. I would never be able to get channel 53 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 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 JBX14WB stacked should work well in areas where signal gain is average (line of site at 30-60 miles), but severe multipath is preventing reliable reception.
 

  


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