Beginners
guide to Amateur Television (ATV)
Adapted from an original article by club member Calvin M1EPM
This
article is intended as a basic guide for getting
started in ATV, it is also worth having a chat with one of the growing numbers of
ATV enthusiasts within MKARS.
Left
is the clubs ATV station, a fine construction project achieved by Calvin M1EPM
and Steve G6ALU
The three main bands used in the UK are 23cm
(1.3GHz), 13cm (2.4Ghz) and (3cm) 10GHz we are lucky enough to be served by
all three in the MK area. The repeaters are as follows:
GB3TG
3cm repeater sited in Brick hill
GB3TV 23cm sited in Dunstable
GB3MV 23cm sited in Northampton
What
ATV band would suit me?
It
depends on your location, ideally you need line of sight to the repeater for
maximum signal. The first and cheapest
check to determine if your location is suited is by using one of the
computer plotting programs available
on the internet, in their simplest form they show a
cross-section of
the land and in some cases can also calculate signal loss. Such plots can only
be used as a guide as unfortunately, trees and
buildings not shown could stifle the signal. In other cases
paths that are blocked by obstructions may well receive signals reflected off buildings
or trees. It may take some time to familiarise yourself with the use of
plotting software so why not ask around the club for some guidance on this?
Each
band has its own advantages and disadvantages, 10Ghz is quick and easy to get
started using modified satellite equipment but it is line of sight only although
signals can
be reflected or "bounced" off buildings. 2.4GHz is also line of sight
but its attenuation in free air is not so great and power amps for 2.4GHz are
cheaper then 10GHz. The most useful frequency for built up areas is 23cm as it
has less attenuation in free air and can pass through objects (but attenuation
will be high). Tthe final advantage is "fringing" which
is the ability of the signal to bend around
objects and the horizon to a limited degree.
When
testing always try the aerial exactly where it is to be fitted as a difference
of a few feet in any direction (even up or down) can have an enormous effect on
signal levels.
What
equipment do I need?
Equipment used will vary depending on the band
required and how strong the signal is in your area; the following is a guide for
the average set-up.
23cm receive
A complete receiver can be
purchased from
www.13cm.co.uk or If you prefer you can modify an old analogue
satellite receiver. Some of these can be a bit on the deaf side but experiments
done by club members show the Amstrad SRX200 and 400 boxes seem to have
a fair amount of gain. As signals for most people will be very weak a
preamp will be needed (mounted at the mast head), not only will this amplify the
signal but it will also have a good output drive that will overcome coax loss
(remember at these frequencies coax cable can be quite lossy). This can be obtained from Bob Platts or the RSGB Microwave Committee.
There are a few ready made aerials available but for an area of average signal level one can be home brewed
as seen in the picture, this was made by James M0BZF.
13cm
receive Here again a complete receiver can be obtained
from
www.13cm.co.uk
an aerial from Masthead Antennas or Sandpiper and a pre amp from the RSGB
Microwave Committee.
3cm receive Here
an L.N.B. (Low noise block) as used in your satellite dish (but with the local
oscillator retuned) is used with or without a dish depending on signal level. To
down convert the 10GHz signal to 1.3GHz (23cm), so this can be run into a
satellite receiver. The output level of an L.N.B. is quite high so a preamp is
not required.
23cm and 13cm transmit 13cms.co.uk has available
ready made units for both these frequencies but they have Iow output power. You
will almost certainly need a power amplifier, a range of which are available
from G.H. engineering. Remember to keep the coax run from TX / power amp to
aerial as short as possible as it is easy to lose half your signal or more.
3cm
transmit This normally consists of a microwave oscillator
(often a gunn diode in a tuned cavity, such as used in alarm movement detectors)
beaming out a signal, a horn fitted to the front of this will greatly increase
the gain. To modulate this 10GHZ signal the voltage to the unit is modulated
with the video
and sound signals superimposed on it, a kit supplied by Bob Platts or RSGB
Microwave Committee can be used
for this
Camera
and monitor A complete set up Tx and RX should
cost you no more than a normal rig. Obviously you will also need to have a TV
with a video input and some sort of camera, an old camcorder would be best but
you can get colour cameras for as little as £20 from rallies.
What
about coax feeder?
RG58 or RG213 are unsuitable as they are lossy at ATV frequencies -
the
coax to use would be H 1 00, Westflex W 1 03 or better.
What
about plugs and sockets?
Because of the high frequencies involved high quality low loss plug and
sockets are required normally SMA and N type. These tend to be on the pricey
side if purchased new but second hand ones on patch leads can very often be
found at rallies cheaply.
ATV
protocol, how do you make a QSO?
In a QSO the party sending the picture sends his
sound on a sub carrier so his sound will be produced from the television or
monitor. If you
transmit ATV the mode for the log is F3F. The person receiving the picture
"talks back" via normal radio usually on 2M 144.750MHz.
Getting up and running
and then to squeeze the maximum signal out of the set up is
enjoyable, rewarding and at times challenging. ATV QSOs are friendly and
informal. Who was it that said, "A picture is worth a thousand words"?
Where
do I get ATV equipment from?
Below
is a list of suppliers and their web sites, they are some of the more popular
ones but its also worth doing your own search on the internet, check the
rallies, and ask around the club for recommendations.
www.radio-kits.co.uk
Steve G6AlU rx and tx controller, information
on satellite receiver modifications
www.ghengineering.co.uk
GH Engineering (power amps for 13cm and 23cm)
www.homepages.ihug.com.au/~promise/G8OZP
Bob Platts (23cm pre amp with filter)
www.sandpiperaerials.co.uk/
Antennas 13cm and 23cm
www.mastheadantennas.com Masthead antennas
(13cm and 23cm aerials)
www.whwestlake.co.uk
Westlake (coax and connectors)
www.g3wdg.free-online.co.uk
RSGB Microwave committee (13& 23cm preamps no filter fitted)
www.batc.org.uk
B.AT.C. (British amateur television club)
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