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Mt. Wilson Shoot-out

Testing Date: 01/08/02

    This test was done to determine which antenna worked best for receiving digital signals from Mt. Wilson. Out of all the antennas I have tried to date, the JBX21WB and JBX21CD are the only ones that can lock on to the weaker upper range channels (59,65,66) from this location. Most of the others work well for the lower range channels such as 31 and 36. I have never been able to get ABC channel 53 from this location with any antenna, but I'm still trying.

    One big difference in this test, is that weather conditions do not have much of a impact on antenna performance. Since I am only 15 miles from transmitter, there is not much weather along the way. This makes the test conditions more stable and I find that repeated tests usually show similar results. Seasonal changes do have a big impact, the trees have more foliage which can either block good signals or reflect bad ones. This can increase multipath, which can kill the ability of your digital receiver to decode a clean signal.

    I am not using a signal amplifier in this test. After the last test, I forgot to mount the amp on the mast and left it dangling from the coax. This caused the amp to fill with water and short out. I have since found that the amp may have done more harm than good. The signal strength readings are much more stable with less fluctuations, the signal only varies about 1%-2%. When I first began testing antennas I found that I needed a amp to help get the San Diego stations. At that time I was using a CM-4248. Now with these more powerful antennas, amplifiers don't seem necessary. I will be doing a future test soon in which I compare several antennas with and without amps.

The JBX21CD will be tested twice. One test will be with the standard 4-element reflector, the other with the newer 8-element reflector.

The JBX21WB will be tested using the new larger 8-element reflector and the updated balun. Without these new parts the 'WB' could not get 59 or 66 at all.

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

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.

Conclusion:

JBX21 WB

  • The 'WB' is designed to be a wide-band antenna (channels 14-69) and the results show it does pull in the lower channels better than the 'CD', but this comes at the cost of less power in the upper range.

  • The lower channel reception was better than the upper channels. A group 'E' antenna (channels 33-69) might be a better choice for our channel range here in LA. The 'WB' would be good for getting both SD and LA since most SD channels are in the lower range.

JBX21 C/D

  • The 'CD' is a  narrow-band antenna (channels 50-69) and the results show better signal reception on channels 59, 65, and 66 than the 'WB', as to be expected.

  • The larger 8-element reflector decreased the bandwidth as seen by the loss of channel 36 and 66. The signal strength increased a little on channel 59. Since the gains were small, I preferred to use the small reflector so that I could also get 36 and 66.

  • The big advantage with the 'CD' over the 'WB' is its ability to get channels 59 and 66, where the 'WB' could not.

 

  


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