[kwlug-disc] Home made indoor TV Antenna

Paul Gallaway paul at gallaway.ca
Tue Jul 8 13:01:53 EDT 2014


On Jul 8, 2014, at 11:38 AM, William Park <opengeometry at yahoo.ca> wrote:
> His 8-bay is advertised as 15 degree.  My 4-bay is 45 degree.

Not trying to pile on but I was planning to respond to this too, and
as already pointed out, 8-bay antennas are directional. Here's some
polar plots that show the difference:
8-bay - http://www.hdtvprimer.com/antennas/cm4228.html (Antennas
Direct DB8 is similar)
typical yagi - http://www.hdtvprimer.com/antennas/W9032.html
4-bay - http://www.hdtvprimer.com/antennas/cm4221.html

The yagi may be slightly more directional, but having a slightly wider
(but still very directional) angle helps with tuning a rotor (you can
be slightly less precise in setting the rotor) while still benefiting
from the directional rejection of co-channels/tropo interference. I
think the only yagi in the Antennas Direct line that bests the DB8 in
max gain is the XG91 (almost 8ft long!). The newer designed 8-bay DB8e
has higher peak gain than the XG91 (subjectively at least) across the
four channels given in the polar plots ($200USD MSRP - yikes! That's a
$100 premium over other 8-bay models or yagis for 1-2 dbi gain) .
Here's the yagi 91XG polar plots for UHF channels 14 (470 MHz) to 51 (698 MHz)
https://www.antennasdirect.com/cmss_files/attachmentlibrary/Technical%20Data%20PDF%27s/91XG-TDS.pdf
The DB8e has some strange side lobbing. It can also be configured so
the two 4-bay antennas that comprise it can be pointed in different
directions (each 4-bay panel turning from 0° to 180°).
https://www.antennasdirect.com/cmss_files/attachmentlibrary/Technical%20Data%20PDF%27s/DB8E-TDS.pdf

For comparison the DB4e does not have the strange side lobbing and is
significantly less directional:
https://www.antennasdirect.com/cmss_files/attachmentlibrary/Technical%20Data%20PDF%27s/DB4E-TDS.pdf

I'm not advocating the DB8e over other 8-bay antennas, but on paper,
it provides the most gain from the readily available commercial
options (there may be others that do better). It hasn't been on the
market very long so not a lot of real world performance information
yet so YMMV. For my next antenna I will probably consider making a
dual bay Gray-Hoverman which has a very good cost performance ratio.
For the record, I do not have a rotor. I will one day consider
building a Gray-Hoverman and ideally gang it with the DB8 before the
preamp (to minimize cost) with the hope being that I can pick up one
or two US channels with the 2BGH (two bay Gray-Hoverman) while
maintaining my Toronto reception with the DB8.

~pAul.

all good things, all in good time...





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