5
So what is this swr (vswr) everyone talks about?
VSWR is a measure of how well two devices are impedance matched to each other. Typical radio equipment is
designed for 50 ohm load impedance, so we usually use 50 ohm cables and build or buy antennas that are specified
for 50 ohm. While most cables have flat impedance over frequency (they measure 50 ohm at all frequencies you are
likely to use) the same is not true of the antennas. A 1.0:1 VSWR is a perfect match. That means the load impedance
is exactly 50 ohms. A 2.0:1 VSWR is obtained when the load impedance is either 25 ohms or 100 ohms.
Because most transmitters will deliver full power with a load VSWR of up to 2.0:1, this value is usually considered
the limit for acceptable operation. Many prefer to keep their VSWR below that however, but for all practical
purposes, it is unnecessary to spend time or money trying to get much below a VSWR of 1.5:1. The benefits will be
hard to measure and even harder to notice.
On the other hand, coaxial cable losses increase rapidly, for a given frequency of operation, when the antenna VSWR
exceeds 2.0:1. This can even, in some extreme cases, result in the coaxial cable burning, even when running 100 W.
Using a higher grade of cable will definitely improve things, but even high quality coaxial cable becomes very lossy
when VSWR exceeds 3.0:1 at higher HF frequencies (or VHF and higher).
BNC connector
A connector is installed at the ends of coaxial cable and connects to the transmitter and antenna. BNC is a standard
VHF RF connector for low power applications, similar to the one used for Ethernet networks. You might get it along
with your antenna. Try to find a good quality BNC connector as PC network type usually uses cheap plastic instead
of Teflon. The good ones are usually easily recognized by much higher prices. BNC to SO239 converters are
available and will make it possible to connect PL259 (CB type or UHF) connector directly. We recommend you
either stick to BNC or use male BNC to female N type adapter, UHF (SO-239) connectors are generally regarded as
of very poor quality and only suitable for CB.
Power supply
You will need a good regulated 12-15 volt, 3A regulated power supply. You can always use a lead acid car battery
and re-charge it when you are off the air. HAM or CB power supply units do the job nicely in most cases. Poor
power supply can add hum to your signal! This unit gives more output power when you run it at 15V, but we do not
recommend using more than that. This is to protect your output transistor; too much voltage can fry your output
transistor, especially if your antenna is not matched well. You can build your own power supply or get one from our
website. Try our web site for schematics, if you want to make one by yourself.
Audio source with mixer, microphone etc
You need something to drive your transmitter. This will typically be either a computer (just plug the cable into your
sound card outputs, a mixer and a variety of audio sources, such as a microphone, CD player, DAT player, tape deck,
gramophone, MP3 player etc.
USING THE CYB
Basically there are three push-buttons available for the menu system,
UP
,
DOWN
and
MENU
. By pushing
UP
or
DOWN
you get a shift of frequency in corresponding direction. Hold any of these keys for a few seconds and the
jumps will increase to 500 KHz. The new frequency is saved automatically. The third button (
MENU)
gives you an
option to set many of the DSP functions of this unit.
THINGS TO REMEMBER
Please remember to turn off the transmitter when not in use! Remember that anything you broadcast through the
transmitter can be heard by anyone tuning in to that frequency. Although it is unlikely certain weather conditions
may allow the signal to go further than your immediate listening area so please don't broadcast anything you don't
mind anyone else hearing.