Shortwave1.pdf

PART 1 – Choosing A Shortwave Radio

There are many different makes and models of shortwave radios, and they vary

greatly in cost, features, size, complexity, and other factors. There is no one

"right" shortwave radio for everyone. The best shortwave radio for you

depends primarily on your listening interests. However, there are some

features and specifications you should look for in any shortwave radio you

consider. They are:

• Frequency coverage. Shortwave frequencies are usually considered those from the

upper end of the AM broadcasting band, 1700 kHz, up to 30 MHz. The minimum

frequency coverage you should look for is 540 kHz to 30 MHz. Most shortwave radios

sold today also tune down to 150 kHz, covering the longwave band.

• Frequency readout. Most shortwave radios sold today have a digital display showing

the frequency the radio is tuned to. A few radios, usually less expensive models, have an

analog "slide rule" frequency readout that does not indicate the precise frequency the

radio is receiving. It can be very difficult and frustrating to find a station on a specific

frequency without a digital display, so a digital frequency display should be a "must"

for any shortwave radio you’re considering. However, an analog readout shortwave radio

can make a good, inexpensive "spare" radio for traveling, etc.

• Modes. Some shortwave radios tune only AM mode stations, and these can be

satisfactory for listening to most shortwave broadcasting stations. However, SSB is used

by a few broadcasting stations in addition to ham, aeronautical, military, and maritime

communications. A shortwave radio that can receive SSB in addition to AM will greatly

expand your listening options on shortwave.

• Selectivity Options. Selectivity is discussed in more detail below, but you need to

consider how many selectivity bandwidths you can select. Some portable receivers allow

you to choose between "wide" and "narrow" selectivity bandwidths, while some desktop

shortwave radios have as many as five selectivity bandwidths. Narrow selectivity

bandwidths let you reduce interference from stations on adjacent frequencies, although

the audio quality of the desired station will be reduced as the selectivity is narrowed.

• Antenna Connections. Some portable radios come with a built-in telescoping antenna

but have no provision for an external antenna. Other portable shortwave radios have a

jack that let you connect an external antenna. Most tabletop shortwave radios have

connectors for external antennas. These usually include connectors for antennas using 50-

ohm coaxial cables and others for antennas using ordinary insulated "hook-up" wire.

External antennas normally give better reception than built-in antennas , although

built-in antennas are usually satisfactory for listening to major international broadcasting

stations. However, built-in antennas give poor results inside buildings with steel frames,

like a high-rise condominium or apartment buildings. In such cases, the ability to connect

an external antenna (even it is only a few feet of wire outside a window) can make a

significant improvement in reception.

Here are some of the terms you need to understand when buying a shortwave radio.

These terms are used to describe the features and controls found on shortwave radios:

Audio filter. This circuit rejects certain audio frequencies in the audio output of a

receiver. A bandpass filter will pass a certain band of audio frequencies but reject others.

A low pass filter will reject all audio frequencies above a certain frequency. A high pass

filter rejects all audio frequencies below a certain frequency.

Automatic gain control (AGC). This circuit adjusts the gain of the receiver to maintain

a relatively constant level of audio output from the receiver regardless of changes in the

strength of the received signal. Some AGC circuits let you select how fast it reacts to a

change in signal strength, such as a "slow" or "fast" AVC. This circuit is sometimes

called an automatic volume control (AVC).

Beat frequency oscillator (BFO). A circuit that produces an internally-generated carrier

to allow reception of SSB, CW, and FSK signals.

Crystal lattice filter. This device improves selectivity by increasing rejection of signals

on adjacent frequencies.

Digital signal processing (DSP). Circuitry in which analog signals, such as audio or

radio signals, are converted into digital form, manipulated and processed while in digital

form, and then converted back to analog form.

Dynamic range. A measure of the strongest received signal that a receiver can handle

with overloading or distortion. It is measured in decibels. A minimum satisfactory

measurement is 70 dB; over 100 dB is preferred.

Memories. These allow storing of frequencies of favorite stations. Some receivers allow

storing of mode, receiver bandwidth, etc., in addition to frequency.

Noise blanker/limiter. This circuit reduces noise due to electrical equipment, lightning,

neon lights, etc. Noise limiters are simpler circuits that limit the maximum strength of

noise pulses, while more complex noise blankers actually silence the receiver during

noise pulses. While this circuits can help reduce noise, they cannot eliminate noise and

often introduce some audio distortion.

Notch filter. A notch filter removes a very narrow slice from a received signal, either

from the radio frequency itself ("RF notch") or from the audio output ("audio notch") of

the receiver.

Passband tuning. A circuit that allows you to move the selectivity bandwidth above or

below the frequency to which the radio is tuned. This is often helpful in reducing

interference.

Product detector. This is a beat frequency oscillator with enhancements for improved

SSB and CW reception.

RF attenuator. This circuit reduces the sensitivity of the receiver in discrete steps, such

as 10 or 20 decibels.

RF gain. A control that permits the sensitivity of a receiver to be continuously varied.

Scanning. This feature lets the receiver automatically tune through a desired frequency

range, stopping on all frequencies where a signal is present. This feature is sometimes not

too useful on shortwave, since atmospheric noise can also can mimic a radio signal.

Selectivity. The ability of a shortwave radio to reject signals on frequencies adjacent to

the desired station. It is usually expressed as a bandwidth measured at 6 dB rejection

points ("6 dB down" or "-6 dB"). For example, a selectivity specification of "6 kHz at -6

dB" means any signal outside the 6 kHz bandwidth will be reduced in strength by at least

6 dB (in other words, the interfering signal is only one-fourth as strong as it would be

otherwise). Typical good selectivity measurements at 6 dB points are 6 kHz for AM, 2.5

kHz for SSB, and 0.5 kHz for CW.

Sensitivity. The ability of a shortwave radio to respond to weak signals. It is measured in

microvolts (µV). The lower the measurement in microvolts, the fainter the signal the

radio can receive.

Squelch. This quiets the receiver audio until the strength of a received signal exceeds a

desired level.

Synchronous detection. A circuit that replaces the carrier in a received AM signal with

an internally generated replacement to reduce the effects of fading.

Variable bandwidth tuning. This circuit allows the selectivity of a receiver to be

continuously varied.

PART 2 – Choosing A Shortwave Radio

The Basics

1. WHAT IS SHORTWAVE RADIO?

Shortwave Radio is a means of radio broadcast, similar to that of medium wave, but

which travels more reliably for longer distances. It is therefore used as a means of

international broadcasting for a number of purposes. International Broadcasting, as

the name implies is transmitting across borders, although the term usually refers to

speech based 'broadcasters.

2. CAN I RECEIVE SHORTWAVE ON A STANDARD RADIO?

Probably not, although this depends on where you live. Most radios sold in the

Western World now receive just domestic FM, Medium wave and perhaps Longwave

(only FM / AM bands in the Americas.) Shortwave radio is for a more specialized

market, and thus requires a more specialized radio. In some parts of the world

where domestic media is not so saturated with stations, shortwave can often be

found on radios sold.

3. ARE SHORTWAVE RADIOS EXPENSIVE THEN?

Not necessarily. Shortwave radios can be picked up cheaply - under £20 / $30 from

your average high street electrical stores. However, you get what you pay for. If you

wish to hear just powerful shortwave stations from your own continent and a little

beyond, a cheap, analogue tuned radio can be sufficient. However, such radios are

imprecise in their tuning, and if you are searching for more distant and weak

stations, you will find your efforts frustrated and often unsuccessful.

If you want to make the best of the hobby from the outset, but don't yet know

whether you are willing to seriously commit yourself to the shortwave listening, try

out a decent portable. The following radios are often recommended: Sony ICF-

SW7600GR, Grundig Yacht Boy 400, Sangean ATS 909 / Roberts R-861. These can

be picked up for between £100 - £200. It's less than the price of a TV or video, and

has the potential to be far more rewarding. Even if you decide not to stick with

Shortwave listening much, you'll have a great radio for hearing domestic stations

further away and with a stronger signal.

4. WHERE CAN I OBTAIN THESE RADIOS?

Your average high street electrical stores may well have some, but not usually the

better portables listed above, and if they do they're usually considerably more

expensive than you can obtain the radios for from mail order companies. Sony

Centers, or similar retailers of Grundig or Roberts etc. will often stock more

advanced radios, but again these are well above mail order price. Look for a

magazine called 'Popular Communications'. Another good source is Ebay.com. Be

sure you get a retail price from a dealer before bidding on Ebay.

5. SURELY TO HEAR FAR AWAY STATIONS I NEED A HUGE AERIAL?

Happily you can receive many stations on the same telescopic whip, which you use

for FM. In Europe this will pull more or less all-European stations of size, and stations

further away too, depending on your radio. On a £17 SW radio I got from Dixons

(British High street Electrical retailer), I regularly heard KOL Israel and US

Commercial stations, for example. On my quality Sony & Grundig portables I can

hear far more. In addition attaching a wire antenna will improve antenna markedly

for more distant and weak signals, and is often thought essential for those living in

weak signal areas such as Western North America or Australia. These areas simply

are long distances from transmitter sites. Such a wire aerial need not be high tech

and fancy - the 'reel' antenna which accompanies many portable SW radios will

improve things, although a 'long wire' antenna outdoors will do so to an even greater

extent.

6. OK, I'VE GOT A RADIO AND AN AERIAL. WHAT NOW?

You can start tuning away! However there are lots of frequencies and broadcasts out

there. Initially it can be quite rewarding and fun to scan through the frequencies and

see what you come across. However you will eventually want to listen regularly to

favorite stations and in a language you can understand.

The two most 'directories' of sorts for the shortwave bands are 'Passport to World

Band Radio' and 'World Radio Television Handbook'. Theses are published annually,

updating the numerous changes in frequencies and sometimes stations, which occurs

each year. These are both great for getting to grips with what is available, although

Passport features more on programming, WRTH concentrating more on the actual

tuning in of stations

Further resources are available on the internet, although radios don't often like all

the radio frequency noise PCs churn out. Visiting a station's website is the best way

for finding current schedules for individual broadcasters.

7. MOST STATIONS AREN'T IN ENGLISH

Shortwave radio is used by most countries of the world to broadcast to throughout

the world. Dozens of languages are spoken, and similarly, dozens of languages are

broadcast, just one of these being English. That said, English-speaking countries are

certainly not the only states to broadcast in the English language. Most broadcasters

of any size do have an English language service. In addition, broadcasters,

dependant on the mandate of the station, also broadcast other widely spoken

European based languages and some broadcasters in many dozens of regional

languages. Each station broadcasts a different selection of languages based upon the

station's role, location and size.

8. I KEEP SEEING AND HEARING 'UTC' EVERYWHERE. WHAT DOES IT MEAN?

Remember that different countries are in different time zones? When trains first

appeared there was a need for a standardization of time between the cities the trains

ran to. Similarly, when shortwave is broadcast and received in so many different

counties, a time standardization is called for. This it UTC or UT, meaning Coordinated

Universal Time, or just Universal Time. UT is essentially the same as Greenwich

Mean Time, as set in London. From knowing UT you can work out your local time in

relation to it. UT never changes, so in summer and winter it always remains the

same, although your local time may change in relation to it.

So for example: the East Coast of North America operates on 'Eastern Time' in the

winter. This is UTC -5. That is, Eastern time is 5 time zones, and therefore 5 hours

behind Universal Time. In summer the clocks go forward in many countries, and

therefore in the Americas move one hour nearer the standard Universal Time. Then

Eastern Daylight Time becomes only UT -4. During summer *some* shortwave

station change their broadcast hours relative to UT so that their broadcast appears to

be at the same local time, despite your clocks having moved forward. As you can

see, this International Time is a tricky business - but with practice you'll get used to

it.

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