SMC Networks HF-150 Operating Manual

1

Getting Started

HF-150

COMMUNICATIONS RECEIVER

OPERATING
MANUAL

South Midlands
Communications Ltd

PR-150

For add selectivity

and rejection of

unwanted signals

AP-150

Digital Audio

Processor for

enhanced audio

output

IF-150

Computer RS232

Serial interface for

ease of control

and auto

frequency

selection

KPAD-2

Keypad for ease of

remote access to

frequency and

mode selection

HF-150 ADD ON ACCESSORIES

HF-150 - Users Manual

3

Getting Started

Contents

Introduction . . . . . . . . . . . . . . . . . . . .4

Getting started

Aerials . . . . . . . . . . . . . . . . . .5

Active Antenna . . . . . . . . . . .7

Connections . . . . . . . . . . . . .8

Types of signal . . . . . . . . . .10

Controls

Front Panel . . . . . . . . . . . . .14

Rear Panel . . . . . . . . . . . . . .16

Operating the HF-150

Volume . . . . . . . . . . . . . . . .18

Modes . . . . . . . . . . . . . . . . .18

Tuning . . . . . . . . . . . . . . . . .19

Keypad . . . . . . . . . . . . . . . .21

Aerial switch . . . . . . . . . . . .23

Memories . . . . . . . . . . . . . .24

Accessory kit . . . . . . . . . . . . . . . . . .25

Care of your receiver . . . . . . . . . . . .26

General notes . . . . . . . . . . . . . . . . . .27

Technical information . . . . . . . . . . .28

(c) 1999 South Midlands Communications Ltd

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Getting Started

The term "Communications Receiver" was originally used in its quite literal
sense to describe a radio receiver which was part of a point to point
communications link. These radio links were normally manned by trained
operators, and Morse Code was the usual method of transmitting information.
Because of the specialist nature of the system and the fact that the operators
were technically trained the communications receiver itself was quite often a
complex piece of equipment.

Over the past twenty or so years, a marked change has taken place in short
wave spectrum occupancy and there has been a considerable increase in
broadcasting, air traffic control, news agency transmissions and so on. The
interest in listening generated by this spread of activity has led to a demand
amongst the general public for receivers which will enable them to keep in
touch with world affairs by short wave radio.

Clearly, these users of receivers are more interested in listening than in the
technicalities of operating the equipment and this in turn has resulted in the
introduction of simpler receivers. However, simplicity of operation has often
been accomplished by a compromise in actual performance, and the results
obtained from some of these simple receivers have been quite disappointing.
As our founder once remarked, "Some receivers are rather like a chocolate
eclair; Wonderful to behold but containing little of substance."

The design and development of the HF-150 was based on

straightforward objectives:­* To obtain sufficient RF performance for the receiver to operate in

crowded short wave bands with many strong signals.
* To combine complete control of a necessarily complex piece of

equipment with easy operation for the user.
* To achieve both the previous objectives within a compact, portable

package at a reasonable price.

We believe that these stated goals have been reached, and that the HF­150 receiver represents a truly new approach to meeting the demands of the
serious short wave listener.

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Getting Started

Aerials and Earths.

Operating the HF-150 is described in the next two sections of this manual, but
you may well ask "What is a suitable aerial?" The receiver has been designed
to work well with a simple long wire aerial, about 10 to 30 metres long. This will
provide good results on most frequencies covered by the set, but if your
interest is in a particular band, such as the 49 metre broadcast band, you may
wish to consider a dipole aerial tuned to that frequency. Do not be dazzled by
the idea of putting up the longest wire in the whole world. This will bring you to
grief, because you will probably overload the input stages of the receiver with
signals from strong broadcast transmitters, with a resultant increase in
background noise.

Where space is at a premium a short wire aerial (a few metres long, maybe
indoors) or a whip aerial can be used. The HF-150 includes a whip antenna
input circuit which optimises its performance with short aerials or in weak signal
areas. However reception, particularly of lower frequencies (long and medium
wave), will be compromised by a short aerial and the receiver will be more
susceptible to locally generated interference.

A good aerial deserves a good earth connection and a ground system
specifically for the receiver is always an advantage. This can be made fairly
simply by driving a metal post into the ground to a depth of about 1 metre and
connecting it to the black ground terminal on the rear panel of the receiver. With
the exception of the 110V model, the mains power supply for the HF-150
provides an earth connection from the receiver to the mains earth system. This
is often adequate for most locations, but in some situations can result in
excessive interference from other mains appliances, which a separate earth
system would avoid.

Long wire aerials should connect to the red terminal on the rear panel of the
HF-150, whereas whips or short wire aerials should connect to the centre of the
co-axial connector - a 4mm plug can be used to connect wires into this - and
the antenna select switch set to the WHIP position. Any aerial systems that
connect to the receiver by co-axial cable (active aerials and dipoles) should use
the co-axial connector with the selector switch in the NORM position.

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Getting Started

The Long wire Aerial.

This is the simplest type of outdoor aerial system, and is very effective for
general short-wave listening. It consists of a single, insulated wire erected with
a horizontal top section and a down lead from one end going to the receiver's
wire aerial input terminal. The wire should be erected as high as possible, and
as far away as possible from other structures or overhead power lines. It can
often be suspended between two buildings or between a building and a tree.
Insulators should be used as shown, and the lead in wire should also be
insulated. The drawing shows a long wire in the form of an "Inverted L," but
many other configurations can be used, such as a slanting wire leading directly
to the receiver.

Other Aerials.

There are several ready-made vertical aerial systems on the market, and they
will provide an easy to erect system occupying very little ground area. They are
normally designed to work over quite a narrow frequency range (typically
amateur radio bands), and for general listening a simple wire will often give
better results.

Active aerials attempt to overcome the problems of very short aerials by placing
a high-impedance amplifier between the antenna and the receiver. The
amplifier must be near to the aerial, so often power is fed to it along the co-axial
cable connecting it to the receiver. The active aerial is very compact, often little
more than a metre long, but a poorly designed active aerial can badly
compromise the receivers performance due to the amplifier overloading in the
presence of many strong broadcast signals.

SMC P2

INSULATORS

LENGTH = 10 to 30m

AERIAL GROUND

RECEIVER
CONNECTIONS

TO AERIAL SOCKET
TO EARTH

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Getting Started

HF-150 MARINE RADIO

IMPORTANT

If you have purchased the Marine Radio version of the HF-150 you should be
aware of the following.

The HF-150 is sent out for normal passive aerial use.
You can use this radio with an active aerial, which will require a 12V DC supply

at the aerial socket.
To make the socket active.
1 Remove the four base fixing screws

2 Remove the bottom cover
3 Connect jumper to bridge the connector at the rear of the PCB.

WARNING: THIS WILL SUPPLY +12VDC TO THE AERIAL SOCKET AND THE
JUMPER SHOULD BE REMOVED FOR NORMAL PASSIVE AERIAL USE

We strongly advise you to label the aerial socket clearly to inform users that
12VDC is present at this outlet.

South Midlands Communications Ltd will accept no responsibility or liabity for
the incorrect use of this feature.

If in doubt consult your dealer.

Suitable Active Aerial

The AA-150M optional accessory is a high performance active antenna which
has been specially designed for the marine version of the HF-150(M).

This aerial has been carefully optimised to match the high performance of the
HF-150M to prevent an overload of signal.

The modification details above will need to be set for use with this aerial.

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Getting Started

Connections.
Power Supply.

The HF-150 receiver can operate from its internal batteries or from an external
DC supply of between 10 and 15 volts. The absolute maximum supply is 16
volts, and if this is exceeded damage may occur to the receiver. The supply
polarity is negative ground only , and although reverse polarity protection is built
in it is wise to ensure that any supply is correctly connected. Be sure that the
receiver power switch is OFF before plugging in or unplugging the power
connector.

In most countries, the HF-150 will be supplied with a small 12 volt regulated
power unit which is designed to operate from the local mains power.
Remember that this supply will be operating all the time that it is connected to
the mains outlet, and it is a wise safety precaution to disconnect it from the
mains supply when the receiver is not in use.

The HF-150M marine receiver is supplied with a 12 volt lead only.
In the United Kingdom the power supply is fitted with a three-core mains lead,

and the earth connection (yellow/green) is connected to the negative (ground)
terminal of the receiver. This provides a reasonable earth connection for the
receiver, but in some cases, where the mains-born interference is prominent, it
will be necessary to provide the receiver with a good RF earth, either in addition
to the mains earth or in some cases instead of it. If the receiver is used with any
other mains power supply it should be able to comply with BSI standards
relating to Class 2 insulation.

Either alkaline-manganese batteries or rechargeable nickel-cadmium batteries
can be fitted to the receiver if it is to be used away from a source of power.
Rechargeable batteries will charge within the set if it is connected to a 12 volt
power source and switched off. For this reason we recommend that non­rechargeable ones are removed from the set if it is used for more than a few
hours on an external supply.

Rechargeable batteries will run the set for three to four hours on a full charge,
and require about 16 hours to charge fully from a 12 volt supply. Charging time
can be longer that this without damaging batteries.

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Getting Started

External Loudspeaker.

A small internal loudspeaker is provided in the HF-150 so that it is self
contained, but although it can provide reasonable all round audio quality,
clearly in the limited space available compromise has to be made. You will find
that if the volume control is set to a high level there may be some audio
feedback caused by vibration induced by the internal loudspeaker. If it is
necessary to operate the receiver at high audio levels, or you want better
quality reproduction the use of an external loudspeaker is recommended.

Because the HF-150 is capable of giving a high quality audio signal, we
suggest you use a good external loudspeaker, a small bookshelf type Hi-Fi unit
is satisfactory. We can provide a suitable unit as an optional accessory with the
correct connecting lead for the HF-150. Any external loudspeaker should have
an impedance of 4 ohms or greater.

Record Output.
Many keen listeners like to tape record any interesting stations they hear, and

a low level audio output has been provided for this purpose.
The REC OUT socket accepts a 3.5mm mono jack plug and provides a level

suitable for feeding into the line input of most tape recorders or amplifier
systems. An attenuating resistor should be added in the lead if feeding directly
into the microphone input of a cassette recorder. The output level at this socket
is not affected by the volume control, so that the loudspeaker can be used to
monitor whilst recording.

The record output can also be used for driving most types of receiver ancillary
equipment such as RTTY, facsimile or Morse decoders. The output level is
about 200m V from a source impedance of 5k ohms.

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Getting Started

Types of Signal.

The HF-150 is equipped to receive most types of transmission likely to be found
within its tuning range, and although most users will be familiar with these, here
are some brief notes on this topic that may be useful to beginners.

AM (Amplitude Modulation).

This was the earliest method used of audio modulation of an RF carrier wave,
and is still almost universally used for long, medium and short wave
broadcasting. An AM signal is fairly easy to tune in, and given a reasonable
signal strength, the receiver may not need to be spot on in frequency. However
when conditions are poor, AM can be difficult to resolve - one particular
problem is frequency selective fading and this is discussed later.

AM Selectivity.

A radio signal occupies a certain portion of the radio spectrum which is known
as its bandwidth. The bandwidth of an AM signal is twice its highest modulation
frequency , and because of this broadcasters are restricted to transmitting audio
frequencies below 5kHz so that they do not occupy too much spectrum. In the
long and medium wave broadcast bands, station frequencies are separated by
9kHz (10kHz in the USA) so there is little or no overlap of adjacent signal
bandwidths. In the short wave bands however, the stations use a nominal 5kHz
spacing, and some broadcasters do not abide by any rules at all, so there is
considerable signal overlap.

The HF-150 is provided with two different AM modes with different filter
bandwidths because of this very problem. If you are receiving a strong signal
in a clear part of the radio spectrum then you can use the standard AM mode
with a 7kHz filter and obtain the best fidelity. The stronger and closer adjacent
stations are, the narrower the filter you will need, and the more muffled the
sound will be because high frequencies are removed. The narrow AM mode
uses a 2.5kHz filter and is necessary in severe conditions, but it is really only
suitable for speech reproduction. When AM mode is chosen you may find that
reception of a station is improved by tuning the receiver slightly above or below
its stated carrier frequency. This is quite a useful technique if there is a strong
adjacent signal that you don't want. As long as the carrier signal is within the
receiver's filter then all will be well, but if you tune too far or select a narrower
filter then the signal will become distorted.

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Getting Started

SSB (Single Sideband).

An AM signal can be considered as a carrier wave combined with two identical
sidebands which contain the modulating audio signal. It is possible to remove
one of the sidebands without losing any vital information, and immediately
halve the bandwidth occupied by the signal. In practice the carrier wave is also
removed (or partially suppressed) to improve transmission efficiency, and the
result is a single sideband transmission.

SSB transmissions are used extensively for voice communication, particularly
to aircraft and shipping, and also by radio amateurs. It is possible to use either
of the two initial sidebands of a signal, so there are two distinct types of SSB
transmission; Upper Sideband (USB) where the sideband frequency is above
the carrier frequency, and Lower Sideband (LSB) where it is below. Nearly all
commercial transmissions are USB, as are amateur transmissions at
frequencies above 10MHz. At frequencies below 10MHz radio amateurs use
LSB by convention.

To receive an SSB transmission, the receiver must reinsert the missing carrier
signal. If this is not done the signal will sound just like Donald Duck - try
listening to an SSB signal in AM mode for this effect. For correct reception the
receiver should be tuned exactly to the carrier frequency, but for speech an
error of 50Hz either way will not be serious. The HF-150 has a very slow tune
rate on its SSB modes to facilitate accurate tuning, but you will need a steady
hand. The pitch of the received voice will change as you tune through the
signal, buy only at one tuning position will it sound like a natural voice. A

2.5kHz bandwidth filter will just accommodate the audio frequencies used for
voice transmission, and this is the filter used for SSB reception.

CW (Continuous Wave, i.e. Morse).

Morse code is usually transmitted by interrupting a single carrier wave, and it
occupies a very narrow bandwidth. In terms of ability to get a message through
under difficult propagation conditions Morse code is one of the most efficient
method, although modern error-correcting digital data systems are also very
good. CW signals are received in the same way as SSB signals, with the carrier
inserted in the receiver producing a beat note with the incoming signal, and
either the LSB or USB modes can be used. Often the one chosen is a matter of
operator preference, or one which best rejects any interfering signals.