Si-tex Navfax200 User's Manual
A
GUIDE TO
S H 0
THE TARGET
r
RT W
RECEIVER
ALAN.
AV
E L I
USING
BY
J.
MULLEY
ST E
HF3
luIQ
N I N G
1
0
The TARGET
30
MHz.
For the beginner, what
The symbol Hz (pronounced Hertz, and named after a famous radio
pioneer) represents one complete electromagnetic wave in a second.
kilohertz (kHz) is one thousand waves per second, and a Megahertz
(MHz),
called the Frequency.
Often a reference is made to a stations wavelength rather than it’s
frequency. High frequency signals have short wavelengths and low
frequency signals have
kHz is given by dividing
a million waves in a second. The number
HF3
receiver covers the entire spectrum from
does
this mean???
of
1
WAVE
IN
1
SECOND
long
wavelengths. The frequency of a signal in
300,000
by the wavelength in metres.
=
1
HERTZ
30
kHz to
waves per second is
A
WAVE
SHORT
HIGH
FREQUENCY
Why are high frequency waves shorter than low frequency
Imagine that you could see a wave travelling past you at the speed of
light. The wavelength would be the distance between two adjacent
If
waves.
more waves in the same space
you increase the frequency of the waves then you would get
MEDIUM
WAVE
so
the wavelength would be shorter.
1
-
-
LONG
LOW
-
WAVE
FREQUENCY
???
Radio waves, light, X rays, are all electromagnetic waves. The only thing
that differentiates them is their frequency.
For convenience the range of frequencies used for radio
communications is split into bands. Frequencies below 100 kHz
'
called Very Low Frequencies (VLF). The Long Wave (LW) covers
frequencies between 100 kHz
covers the frequencies between 300 kHz and 1.6 MHz (1 600 kHz).
All
frequencies between 1.6 MHz and 30 MHz are referred to as Short
(S
Waves
I
-
VLFl
W).
LW
and
300
kHz, whilst the Medium Wave (M
MW
are
sw
W)
I
The
HF3
covers all of these bands in one continuous sweep with steps
of 1 kHz.
those to the right are
e.g.
Turning the tuning knob slowly advances the tuning in 1 kHz steps,
turning a little faster the steps change to 10 kHz,
become 100 kHz,
This makes it quick and simple to hop from one end of the spectrum to
the other.
Numbers to the left of the decimal point are in MHt whilst
in
kHz.
0.198 is expressed as 198 kHz or 0.198 MHz
14.386 is expressed as 14386 kHz or 14.386 MHz
faster still the steps
and a really fast spin will make the steps 1 MHz.
2
GETTING
The
HF3
phono plug. The wire length is
general coverage.
longer wire may pick up more of the desired signal,
much more undesirable signals in the form of interference. The
antenna wire should be strung up as high as possible and as far away
from mains wiring, striplights, televisions, or any other source of
interference (see Page
is the ground terminal. Connect this to something that is well
grounded.
not connect to anything
*Do
not
aid of a qualified Electrician.
STARTED
is supplied with a simple long wire antenna connected to a
30
feet and is a good compromise for
A
shorter wire will be less sensitive and, whilst a
it
may
also
pick up
9).
The shorter black wire from the phono plug
A
cold water pipe or *mains earth is usually adequate.
you
are not certain is earthed.
attempt to connect directly to any Mains Supply without the
Do
Plug the
the antenna and set the attenuator on the rear of the receiver to it’s
normal position. You are now ready to go.
Switch on the receiver by rotating the volume control clockwise. The
display
select mode
modes. Set the Clarify control to it’s central position. Adjust the volume
to a convenient level and use the tuning knob to move up and down
the spectrum and listen to the
To
Tune to the desired frequency and press
becomes the memory location pointer. Select the memory location
using the tuning knob. When the desired location is selected press
MEM,
returned
12
Volt line from the power supply into the receiver, plug in
will
show the frequency and the mode. Set the mode to AM. To
USB,
AM and
LSB
press
AM stations.
MOD.
This rosters through the
Store a Frequency In memory
MEM.
the desired frequency is stored in that location and the receiver
to
normal operation.
The S meter then
3
To
Recall a Frequency from memory
Press
RCL.
The S meter then becomes the memory location pointer.
Select the desired memory location using the tuning knob. When the
desired location is selected press
RCL.
The desired frequency is
recalled and the receiver returned to normal operation.
The
RST
key resets the microprocessor and reverts to memory
position 1.
Tune to 100 kHz
and you will hear a fast ticking noise. These are the
pulses of LORAN C, this is a long range navigation system in use all
over the world.
A
little lower in frequency, between 80 and
90
kHz you
can hear the carriers of the DECCA system. This system was set up in
1944
for the D day landing and has been in continuous maritime use
ever since. Encrypted data is transmitted to military submarines at
VLF.
This covers very great distances. Speech is not transmitted.
The Medium and Long waves are crowded with domestic and foreign
broadcast stations. When tuning a station rotate the tuning knob to
obtain the highest number on the
Tune between
300
and
400
Signal Strength Meter.
kHz for marine and aeronautical beacons.
These are used by shipping and aircraft to get bearings. Each beacon
transmits a Morse code ident of it’s name. The Morse is very
continually repeats,
so
if
you don’t read Morse, you have plenty of time
slow
and
to look it up. The ident letters are often a syllable of the airport or
towns name.
Domestic portable telephones operate at the high frequency end of the
medium wave at about 1.6 MHz.
A
frequencies start.
quick flip round and you’ll find it’s very different
At 1.8 MHz the short wave
than the medium wave band.
The BBC broadcasts it’s World Service on several short
BBC
frequencies. In times of crisis the
World Service has been the
-
wave
source of unbiased news the world over. Most countries have their
own overseas broadcasts. Some follow in the traditions of the BBC,
others simply use the airwaves for blatant propaganda.
4
Many overseas broadcast stations welcome contact with listeners.
This helps them to establish their listener profite and assess their
coverage. The station will usually repay the listener with give
-
away
goodies and a QSL card (from the international Q code meaning
“acknowledge receipt”). Many people make a hobby of collecting QSL
cards from
all
over the world.
Some transmissions will not contain speech or music, they
will
just
consist of warbling tones. These contain some form of data. It may be
a weather chart broadcast to shipping, or a fax or telex to a news
agency. Without a special decoder it cannot be read.
Another form of transmission found on short
(SSB).
-
wave is single side band
To understand what this means it helps to see how it developed. In a
conventional signal a carrier is transmitted. The amplitude (height
of
the wave) of the carrier is modulated with speech, hence the name
“amplitude modulation” (AM).
If
the signal is studied carefully then the
result of the modulation produces a carrier, an upper sideband of
frequencies and a lower sideband of frequencies.
All
this takes up space on the radio spectrum. Now, since the upper
and lower sidebands are mirror images of each other it’s not
necessary to transmit both,
so
one is filtered out in the transmitter. As
no information is provided by the carrier that also can be filtered out
leaving only one of the sidebands. This takes up less space in the
spectrum and, because only wanted information is transmitted, makes
better use
This is single sideband or
of
the power available.
SSB.
The downside of this is, firstly, the
quality of reproduction is not usually as good as AM. For this reason it
is only used for communications and not for broadcast. Secondly, it is
more difficult to recover the original speech than in AM.
When recovering an
SSB
signal, the listener must know which
sideband is being transmitted. Fortunately there is a convention.
Frequencies below 10 MHz
those above 10 MHz
use the upper sideband
exceptions to this convention, e.g.
transmit the lower sideband (LSB), and
(USB).
(There are
the R.A.F. VOLMET on 4717 kHz)
5
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