Australian
TV Band 4 / 5 ( IV / V ) log-periodic yagi
- covering 500 to 850 MHz -
- with VHF add-on elements -
built to use with a USB digital TV tuner stick..
August
2009
----------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------
|
We are starting
to use our camper trailer more for a few breaks away from home and
since I always seem to take the notebook computer with us anyway,
there was a thought about buying a USB tuner stick to plug in and
be able to watch TV - only as necessary, of course. That means that
a single device (i.e the notebook) can take the place of a stand-alone
TV, with or without DVD player for those rainy days, card games
computer, music source, and internet gateway - a saving on space
that is most important when moving around with our camper trailer
and trying to fit all our "extra bits" in..
Accordingly
I went to one of the local computer retailers and bought what turned
out to be an AV Labs AVL680HD high definition digital tuner stick
(for Win XP-SP2 / XP-MCE / Vista only) for about $Aud40 - including
GST. I dutifully powered up the notebook, installed the software
from CD, plugged in the tuner and supplied antenna ( connects via
thin coax and a PAL plug ) and set it scanning for signals. It found
some of the standard definition digital channels on VHF and all
on UHF as well as the local HD ones on UHF.
Of course,
there are many other similar USB TV tuners available cheaply these
days and it is simply a matter of what is available to you - and
whether you want just digital TV or want to include analogue TV
as well (at a higher price). Just remember that analogue TV coverage
in Australia is already starting its phase-out, will be gone by
around 2012/2013, and all analogue programme is already available
on the digital channels anyway..
|
<--
USB 2.0 socket
|
|
<--
PAL female external antenna socket
|
Moving the
supplied small 'modified' whip antenna around made a huge difference
as to what channels could be received. It worked fairly well when
attached to the side of the fridge (using its internal magnetic
base) (thus horizontal polarisation) but standing vertically on
the wooden table was hugely ineffective. Obviously if we were going
to use it at various locations around the countryside, a better
antenna was going to be required. Since most of the places we were
likely to visit would have UHF coverage either from prime transmitters
or via translators, I decided a single broadband antenna covering
500 to 850 MHz was in order, hopefully not so big that it would
be a problem to transport. That would then cover both Band IV and
Band V ( 4 & 5 ) services. The only style that would provide
that sort of bandwith coverage was a log periodic yagi ( or LPY
).
A bit of
Google web searching later producd a LPY calculator (in french)
at http://alain.caupene.club.fr/Log_periodic.htm
and by entering my desired upper and lower frequencies came up with
some dimensions to build from. Please note that the calculated dimensions
are tip-to-tip and the physical construction has to take that into
account. I ended up choosing a 13 element design that required a
boom length of just over 1 metre ( actual 1039mm), longest element
at 300mm, shortest at 177mm, as best suiting my needs. Of course,
others may want smaller or larger variants and the calculator will
allow you to create those. My physical device was going to have
to be robust (to survive the transit and packing phases) and having
materials left over from the 23cm yagi
project made that job easier. The elements were mounted using
the same methodology but being a LPY, two spaced parallel booms
were used.
This page
is not going to be a step-by-step guide to building an identical
antenna - simply a set of photographs with comments and basic dimensions
about how it can be done. They say a picture is worth a thousand
words and there are enough pictures on this web page to nearly write
a small book. Certainly the methodology used in the construction
should be fairly obvious to most who do a little "handy-work"
in their workshops and aren't afraid to cut metal and drill holes.
Main materials
used : 15mm square aluminium tube, 1/4" / 6.2 mm round aluminium
rod.
| Element
Number |
Total
Length (Tip-Tip) mm |
Half
Length Cut (mm) for 15mm mount tube
(2
required each length) |
Spacing
to next element (mm) |
1
(lowest freq) |
300 |
165 |
109 |
| 2 |
287 |
159 |
104 |
| 3 |
275 |
153 |
100 |
| 4 |
263 |
148 |
96 |
| 5 |
252 |
141 |
91 |
| 6 |
241 |
136 |
88 |
| 7 |
231 |
131 |
84 |
| 8 |
221 |
126 |
80 |
| 9 |
211 |
121 |
77 |
| 10 |
202 |
116 |
73 |
| 11 |
193 |
112 |
70 |
| 12 |
185 |
108 |
67 |
13
(highest freq) |
177 |
104 |
Boom =
1039mm + front +rear mount allowances (Allow 1200mm) |
Half Length
Cut (mm) for 15mm mount tube
column is half the length plus the mounting tube external dimension
(i.e. 15mm)
as the rod passes through from side to side & thus still has
the desired length exposed on one side and is flush on the other.
|
Simply mouse
over any image to see a higher detail image.
This is the basic LPY assembled - the front is the narrowest end (LHS
above) and should be pointed towards the TV transmitter site. |
The mounting/spacer blocks are "T" shapes with holes drilled
through the tops of the "T". Note that the elements protrude
from alternate sides of the two booms once assembled : eg bottom,
top, bottom, top... on the LHS of the photo. When you are making it,
the two booms with elements are identical and one is simply "flipped
over" when being attached to the "T" insulator blocks. |
The "T" blocks are used to insulate and separate the two
15mm square boom tubes. The screws and wingnuts are 3/16" whit
and because of clearances to the front-most elements are mounted
from alternate sides. The boom-boom spacing is about 10 - 12mm but
is not super critical.
As noted below,
the material is cut from 12mm kitchen "chopping board"
- very easy to cut with a saw and then drill.
|
|
The rear insulator is another "T" section identical to
the front one. The set of 2 holes in the sides of both boom tubes
allow the assembly to be rear-mounted. The extra holes in the tops
are not required but were drilled when the vertical/horizontal mounting
arrangements were not yet finalised.
|
This set of 2 holes per boom is used for centre-mounting the antenna
and is the normally used position.
The blue permanent marking pen just makes it easier to assemble by
matching up the similar blue marks. |
The element holes are drilled right through the boom tubes at the
spacings given in the table above and then reamed out slightly so
that the element material is a tight fit into the hole on both sides.
The elements are then tapped into place such that the end is flush
with the sidewall of the boom |
This view shows the rear T insulator a little more clearly - with
the two 3/16" wingnuts on the same side - as there is no element
clearance issue |
The mounting block/insulators were cut from a 12mm thick kitchen "chopping
board" drilled as required to suit the 3/16" screw hole
positions in the booms and the 5/16" U-bolt. |
The other side of the mounting block shows the flat washers under
the screw heads and the wingnuts on the U-bolt threads
|
The mounting block/insulator as screwed onto the boom at the centre
mounting position. You will probably note that there is an element
protruding through a hole between the two uppermost screws and that
the very end of the lower element is visible in the hole between the
lower screws. These hole sets allow the same mounting block to be
used at the rear or the centre position. |
.
Opposite side view showing the lower element protruding through
the hole
The extra hole
visible below the protruding element actually lines up with the
U-bolt when set up as vertically polarised - the metal top prong
of a tent pole fits into the hole to help stabilise the assembly.
|
Why use wingnuts
???
The antenna
has to be able to be assembled and then pulled apart - at the beginning
and end of any camping stay - just to save storage space. Wingnuts
make it quick and easy and it is usually easier to see where a wingnut
is when you drop it in the grass (and 'Murphy' says that it will
happen !) .
If your antenna
was for more-or-less permanent mounting, wingnuts are not required
but spring washers and nuts are...
You still
need to use the flat washers as the white chopping board material
is soft-ish.
|
The connection to the tuner card is via the PAL plug (bottom) and
the other end is terminated with an "F" connector that screws
onto the end of the TV balun (top, inside the weather sleeve), which
is fitted with spade lugs to go under the screws at the front of the
LPY. |
This is the entire connection cable - 10 metres of 75 ohm low loss
foam dielectric coaxial cable, PAL-male plug on one end to the balun
with spade lugs on the other |
The spade lugs on the balun are simply placed under the 3/16"
whit screws at the front of the antenna - note that the balun must
be fitted at the front of the LPY(the narrow end) - NOT the rear. |
The mounting pipe is fitted into the U-bolt and the wingnuts tightened.
As shown, the antenna is set up for horizontal polarisation. |
With the 90 degree mount bracket in place, the antenna is now set
up for vertically polarised TV signals. |
This is a top view of the mount when set for vertical polarisation |
This is actually an "underneath view" of the mounting arrangement
for vertical polarisation. The U-bolt is used this way around specifically
so that the centre of gravity of the antenna is closest to the mounting
pipe. |
This is the view from the front of the antenna showing the positions
of the mounting tube, the 90 degree bracket and the various wingnuts |
This right angle piece is used to change the antenna from horizontal
to vertical polarisation. The bolts are also 5/16" whit with
wingnuts and flat washers, to match the threads on the U-bolt.. The
spacing of the 2 sets of 2 holes is also set to exactly match the
U-bolt thread spacing |
To extend the frequency coverage where VHF digital TV is available,
4 extra extensions were made from additional 6mm rod pieces plus the
compressible sleeve part of 1/4" Dynabolts tapped on and then
covered with heat-shrink plastic tubing. |
These VHF extension pieces are fitted onto the end of the two rear-most
elements and provide additional frequency response down in the
150 to 220 MHz range when fitted. |
VHF extension
pieces :
2 at 280mm
2 at 200mm
About 20mm of each length is inside the fixed long section of the
'ex-Dynabolt' joining collar.
The 3-expansion
fingers "collar" pushes-on over the basic element for
15mm.
This gives a
total approximate element length for #13 as 600mm (~150MHz) and
#12 as 750mm (~200MHz) providing basic support for VHF TV channels
5A to 11.
|
Using the antenna
above made a gigantic difference to the received signal level as indicated
by the little bar meter/indicator near the top of the "TV" display
on the notebook. The TV signal would no longer drop out when someone walked
nearby - as it did with the small antenna supplied with the tuner. All
in all, it looks like the results were worth the couple of hours spent
working out how to mount/insulate the booms and creating the "T"
end spacers, cutting the tubing and rod.
Total materials
cost - about $25 - $30.
NOTE
: I tried the USB tuner in the side of my IBM notebook and it worked fine
- BUT plugging it into a USB port on the back made it seem like it was
faulty. Windows XP found it but there were no TV channels found on scan
etc... Back in the side was ok. Obviously some ports on the notebook are
capable of supplying sufficient power to the tuner and some aren't. If
your tuner doesn't work, try another true USB 2.0 port or via an external
2.0 hub with an external power supply before thinking it is faulty..
A web advert
for the USB tuner I purchased :
|
AVLabs
AVL680HD - USB High Definition Digital TV Tuner
With
the AVLabs USB High Definition Digital TV Tuner, you can enjoy watching
or recording digital TV on your computer or laptop anywhere, anytime!
You can watch and record digital TV with the time-shifting function,
you can even pause live TV! With schedule recording you won’t
miss any of your favourite shows.
Supports HDTV
Watch and record digital high definition TV in any country with
digital reception.
Bundled with
HyperMedia Center
The AVL680HD with HyperMediaCenter, a powerful multimedia player
for all purpose. In addition to the basic functions for a multimedia
player, when it is paired with DVB-T Stick Pro it also scans and
recognizes channels automatically, and enables users to preview
9 channels at once. You can also adjust setting such as brightness,
contrast, hue and saturation.
Supports Electronic
Program Guide(EPG), Subtitle
Watch additional information, such as subtitlesand program guides.
3 Easy Steps
to Plug and Play
Just plug the DVB-T Stick Pro into any computer system, follow the
on-screen instructions to install the software application within
minutes you will be watching HDTV.
Features
- Watch free-to-air digital TV and listen to digital radio on your
PC or laptop
- Comes complete with HyperMedia Center, a powerful user friendly
application that allows you to:
- Watch or record digital TV
- Auto channel scan and name recognition
- Multiple channel preview
- Brightness/contrast/saturation/hue adjustment
- Supports HDTV
- Supports EPG and subtitle function (DVB standard)
- Supports time-shifting and scheduled recording function
- Supports still image capture in JPEG or BMP format
- AVL680HD is compatible with Windows XP, Windows Media Center &
Vista
System Requirements
- Pentium-IV 1.6 GHz or higher recommended (recommended 2.8GHz for
HDTV)
- 256MB RAM of system memory or above (recommended 1GB for HDTV)
- One available USB2.0 port
- Graphics card (Must support Microsoft DirectX 9.0C or above)
- Sound card (AC97 compatible sound card)
- 1GB Free HD space
- CD-ROM Drive (For software installation)
- Microsoft DirectX 9.0c• Microsoft Windows XP SP2 / XP MCE
/ Vista
Package Contents
- USB Digital TV Tuner
- Antenna
- Installation quick guide
- Installation CD
- Remote
|
Any
feedback would be appreciated :
Feedback Form
Last
edit
:
25-Mar-2010
|
