1/9/08

The AntennasDirect  DB-8  8-Bay

 

http://www.hdtvprimer.com/ANTENNAS/DB8.jpg

 

http://www.hdtvprimer.com/ANTENNAS/DB8az.gif

http://www.hdtvprimer.com/ANTENNAS/DB8el.gif

 

The performance of this 8-bay roughly equals the Channel Master 4228.  While the smaller screen hurts the DB-8 some, it has a better feed system than the 4228.

 

Note that the gain graphs are the result of simulations, and those simulations did not include the loss in the combiner.  The author has not yet measured this combiner.  Combiners often lose 1 or 2 dB at the highest channels.  (Balun loss also is not included for this or any other antenna.)

 

The right and left dipoles are set farther apart (by 3.4 inches) on the DB-8, compared to the 4228.  This results in larger minor lobes in the azimuth (view from overhead) pattern, but it also narrows the main lobe.  As a result the DB-8 is probably better at rejecting multi-path than the 4228.  The major null is at about 25° for the DB-8, 30° for the 4228.  The following table shows the beam widths (measured to the half-power points):

 

ch 20:       ch 30:       ch 40:       ch 50:       ch 60:       average:     

DB-8            25.3°         23.2°         21.0°         19.0°         17.7°         21.2°

4228            32.2°         26.2°         25.7°         22.3°         19.4°         25.2°

DAT-75       44.3°         39.2°         34.8°         30.5°         26.6°         35.0°

 

This antenna has been optimized for the higher UHF channels while its competitors, the Channel Master 4228 and the Winegard PR-8800, have been optimized for the lower UHF channels.  The DB-8 performance is nearly identical to the XG91, making one wonder why AntennasDirect sells both of these antennas.  After 2/17/09, when the higher UHF channels are gone, the DB-8 will be at a distinct disadvantage when compared to the 4228 or PR-8800.

 

AntennasDirect calls the DB-2, DB-4, and DB-8 “Multi-directional antennas”.  There is good justification for calling the DB-2 and DB-4 multi-directional, but the DB-8 is one of the most directional antennas you can buy.  AntennasDirect is simply flat wrong about this.  You must keep in mind that an 8-bay is very different from its kin.

 

The simulations show a problem at channel 16 for the DB-4 and DB-8.  This is the result of a resonance (large current) in the vertical rods that support the dipoles.  The author has not measured the real antennas to verify that this resonance is not below channel 14.  (The simulation could be slightly off on the frequency of this resonance.)

 

High gain antennas like this one are big, hard to aim, and hard to keep up in bad weather.  The author does not normally recommend this antenna inside 25 miles.  But there are two exceptions to this:

  1. A very high gain antenna might be necessary behind a hill or in a valley.
  2. When an obstruction is causing multi-path, a very directional antenna such as this one can reject signal from the wrong directions.

 

 

 

 

 

 

 

 

This page is part of “An HDTV Primer”, which starts at    www.hdtvprimer.com