Brought to you by PCS Electronics, www.pcs-electronics.com
15
Before you start
It is recommended that you read this section before you power your unit up for the first time. Let us clear up some basics
you should know about. You will also find some useful tips in our guides and forum at
http://www.pcs-electronics.com
.
Here is what you need to get your TV transmitter on the air:
Antenna
Preferred type of antenna is affected by several factors, but mostly by desired radiation pattern, space available and your
budget. If you are located in the middle of the area you want to cover you'll need an omni-directional antenna which
transmits equally in all directions. If you are located at the edge of your desired coverage area you can beam the signal into
the target area with a directional antenna. Directional antennas are also practical for point-to-point communications.
Another thing to consider is that directional antennas usually have much higher gain than omni-directional antennas since
the power which is radiated in all directions with omni antenna is concentrated mainly into one direction with directional
antenna. Antennas with more gain thus have narrower beam. A compromise is usually made depending on budget and
space available, higher gain antennas are often bigger and often more expensive.
Once you’ve chosen and installed your antenna there is another thing to consider. You can read more about it in the next
section (So what is this SWR everyone talks about). Before powering up your transmitter on the air you should tune your
antenna to get minimal SWR. This is typically done by adjusting the position of the antenna and any adjustable pieces. Aim
for 2:1 or less. Use low power into the antenna when tuning it up and making adjustments. If you were using full power and
a bit of the antenna came off in your hand the VSWR could be so bad as to blow the final transistor. For the same reason
check the DC continuity of the antenna with an ohmmeter before plugging it in, to be sure it's what it's meant to be, either a
short circuit or an open one, depending on the antenna type. For instructions regarding construction of antennas please see
our website:
http://www.pcs-electronics.com
(guides section - antennas).
Antenna is a crucial part of the system so take special care. It is usually a good idea to place antenna away from your
transmitter, power supply and audio system. Also any transmitter should be in a metal case which shields circuitry from the
radiation of the antenna. If you cannot meet these requirements, you could experience feedback and other RF problems. We
cannot guarantee proper operation of any transmitter/amplifier unless suitable antenna system is used and transmitters are in
ventilated metal enclosure! This applies to any transmitter. Interestingly, strong RF field can make CD players and other
digital devices go bezerk. Try placing antenna next to yours and see what happens. Most of the modern audio gear is not RF
shielded – reducing costs is unfortunately the mantra today. This is why keeping antenna away from audio gear is a good
idea.
If you are going to place your antenna outside, on your roof, please take care of the grounding. This should be done to
prevent lightning hazard and should be done by a company specializing in lightning protection. You can read more about
lightning protection in the book recommended below or many of the websites (Google up “lightning protection ham radio”
for example) .
I hope this basic introduction will not scare you too much, it should be sufficient for the time being although we encourage
you to explore this exciting subject further with the help of a book such as the ARRL Antenna Book:
http://www.amazon.com/exec/obidos/ASIN/0872598047/mightyspiraterad
Chapter
4
