[NLRS] Is there published data on tree foliage ...

[Doug Reed]

The little bit of reading I've done on the subject says that for DTV,
multipath is the major player, not signal strength, particularly for
those of us so close that the old wet noodle should be enough antenna.
Think back to your analog TV days. How often did you see a "shadow
fringe" along the edge of people or objects on the screen? That shadow
was caused by multipath. The spacing between the object edge and the
shadow edge was the delay time. How "hard" the shadow edge was
indicated how strong the multipath signal was. It was usually annoying
but seldom enough to prevent watching the picture.

But on DTV, strong multipath can cause loss of picture because it
smears the digital data enough that it can't be received and recovered
digitally. But out in the boonies, if you get your antenna up enough
to minimize multipath, your picture will be perfect! I've got a little
7" portable LCD I've been using with its rod antenna and it was lousy,
barely about 8-12 stations and they'd go away when I moved. With even
a minimal UHF antenna I get about 35 stations and the reception is
more "stable".

My reading shows that the 2, 4 and 8 bay bowtie antennas are probably
the best for broadband TV reception at UHF. I found a number of sites
that ran comparisons of various UHF antennas and the bowties were
usually considered the winners. By "winner" I mean a broad, fairly
flat gain curve covering as much of the 450-700MHz UHF band as
possible. You just have to wrap your mind around paying $50 to $150
for a UHF antenna that you can't transmit on.... :-)

<http://www.digitalhome.ca/ota/superantenna/>
A bit of searching turned up this antenna site. The Gray-Hoverman
antenna is frequently talked about on the OTA sites as an excellent
antenna for DTV long range. And as a high gain antenna, it is also a
more directive antenna so multipath should be reduced. If you look at
the G-H and have any of the old Dubus(?) microwave compendiums, the
G-H looks an awful lot like the double diamond and quad diamond UHF
antenna designs. This is a decent antenna that you can build from
scraps or maybe $10-$15 of materials.

The best thing about the G-H antenna is that it is made from two
continuous lengths of wire bent to shape so there are only two
connections (for the 75-ohm transformer) that might get intermittent.
If you lay it out on a board and drive some nails, you can form the
elements as fast as you can stretch, bend, and cut the wire.

The next most popular antenna is a home brew version of the bowtie.
They are really pretty easy to build and they can be as simple to
build or as complex as you want. The two common designs are either the
"cats whisker" bowtie or the flat plate triangle bowtie. The "cats
whisker" is definitely the best version if you will mount it outdoors
since the wire elements have less wind load. For the flat element
design, the problem is making the elements strong enough to survive
wind loading with minimal expense.

As a "proof of concept", I took a large sheet of cardboard to use as
the antenna backer, and cut two identical elements out of tin foil,
taped them to the cardboard, and attached a 75-300 ohm transformer in
the middle at the feed point with screws, nuts, and washers. With that
standing on top of a file cabinet and pointing more-or-less out the
window I get about 35 stations. I basically used the "MCLAPP 9.5"
dimensions" to build a 2-bay flat plate bowtie. My cardboard was too
small to extend it to 4-bay.
<https://sites.google.com/site/maycreates/ota-setup/mclapp-4>
<http://m4antenna.eastmasonvilleweather.com/Drawings/PDF%20Drawings.html>

The basic cardboard sheet bowtie is bi-directional. To make it
unidirectional, just add a reflector about 4"-5" behind the bowties.
Some of the outdoor designs use PVC pipe to make a frame and attach
the elements to the pipe. Some just use a wood 2x4 on edge to mount
the bowties and reflector. I was just going to hang my cardboard
antenna from the rafters in the attic.

<http://www.youtube.com/watch?v=YaYDtOqpTOI>
If you go to YouTube and search for HDTV home made antenna, or bowtie
antenna, or Gray-Hoverman antenna, you will find lots of examples. The
video I most enjoyed was the two 10-year old kids explaining and
building the antenna, that is the level of complexity. :-)  My
cardboard HDTV antenna was zero cost because I had tin foil,
cardboard, tape, and the 75-ohm transformer already.... I just noticed
that one of those cardboard "Project Display Boards" (about 27"x40")
is just about right for a 4-bay bowtie....

If you want to do some more reading, the digitalhome.ca web site
seemed to have the most active Over-The-Air hobby groups. At least I
thought it had the most discussion and lead to the most options.
<http://www.digitalhome.ca/forum/forumdisplay.php?f=81>

If you don't already have an outdoor UHF antenna for your TV set, give
it a try to make your own antenna and see what happens. If it does
improve your reception, then you can decide if your homebrew antenna
is good enough or if you want to buy a similar size or larger
commercial antenna.... But if you are trying to get along without a
real antenna and good coax feedline, you shouldn't be surprised by
crappy results.

Regarding the question was ATSC designed for Over-The-Air or cable-TV,
it is an OTA protocol. Your cable company converts the ATSC signal to
(DVB-C?) QAM format before it is put on the cable. DVB-T and ATSC are
both designed for OTA. DVB-S was optimized for the problems you see
with satellite service and DVB-C likewise optimized for cable TV.

73, Doug Reed, N0NAS.