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Antenna Stacking Test - JBX08WB

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 JBX08WB antennas in this test. These antennas are very similar to the popular JBX21WB tested here, except they are shorter and have only 8 director elements. As seen above, these can be mounted at the end of the boom making for a very neat installation, but a boom support tube is also included. 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

jbx08wb 001.jpg (61182 bytes)

Channel 31

jbx08wb 001.jpg (61182 bytes)

Channel 31

jbx08wb 052.jpg (62754 bytes)

Channel 31

jbx08wb 036.jpg (62553 bytes)

Channel 31

jbx08wb 044.jpg (61884 bytes)

Channel 31

jbx08wb 002.jpg (61300 bytes)

Channel 36

jbx08wb 002.jpg (61300 bytes)

Channel 36

jbx08wb 053.jpg (60729 bytes)

Channel 36

jbx08wb 037.jpg (62772 bytes)

Channel 36

jbx08wb 045.jpg (61535 bytes)

Channel 36

jbx08wb 003.jpg (61357 bytes)

Channel 42

jbx08wb 003.jpg (61357 bytes)

Channel 42

jbx08wb 054.jpg (63832 bytes)

Channel 42

jbx08wb 038.jpg (61303 bytes)

Channel 42

jbx08wb 046.jpg (61227 bytes)

Channel 42

jbx08wb 004.jpg (61002 bytes)

Channel 53

jbx08wb 004.jpg (61002 bytes)

Channel 53

jbx08wb 055.jpg (61480 bytes)

Channel 53

jbx08wb 039.jpg (61594 bytes)

Channel 53

jbx08wb 047.jpg (62219 bytes)

Channel 53

N/A

 

Channel 59

N/A

 

Channel 59

N/A

 

Channel 59

N/A

 

Channel 59

N/A

 

Channel 59

jbx08wb 005.jpg (61457 bytes)

Channel 60

jbx08wb 005.jpg (61457 bytes)

Channel 60

jbx08wb 056.jpg (62049 bytes)

Channel 60

jbx08wb 040.jpg (61216 bytes)

Channel 60

jbx08wb 048.jpg (61820 bytes)

Channel 60

jbx08wb 006.jpg (61474 bytes)

Channel 61

jbx08wb 006.jpg (61474 bytes)

Channel 61

jbx08wb 057.jpg (64265 bytes)

Channel 61

jbx08wb 041.jpg (61611 bytes)

Channel 61

jbx08wb 049.jpg (63060 bytes)

Channel 61

jbx08wb 007.jpg (61015 bytes)

Channel 65

jbx08wb 007.jpg (61015 bytes)

Channel 65

jbx08wb 058.jpg (63059 bytes)

Channel 65

jbx08wb 042.jpg (61509 bytes)

Channel 65

jbx08wb 050.jpg (62453 bytes)

Channel 65

jbx08wb 008.jpg (60716 bytes)

Channel 66

jbx08wb 008.jpg (60716 bytes)

Channel 66

jbx08wb 059.jpg (61230 bytes)

Channel 66

jbx08wb 043.jpg (60544 bytes)

Channel 66

jbx08wb 051.jpg (61276 bytes)

Channel 66


Conclusion:

  • I found the shape of the JBX08WB waveforms to be very similar to the JBX14WB and 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 8 element antenna has less gain than the 21 element. On most channels in my location, the signal was too weak to lock in even though the shape was free from multipath.
  • 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 JBX08WB stacked should work well in areas where signal gain is high (line of site at 15-30 miles), but severe multipath is preventing reliable reception.

 

  


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