WHAT HAVE RADIO WAVES EVER DONE FOR US?
Well radio waves have carried Terry Wogan, Tony
Chris Tarrant and Coronation Street to us - riding on the wave, that's
waves are part of the Electromagnetic
Spectrum. All waves of the electromagnetic spectrum
travel at the same speed of 300,000 kms per second in space. Note
that sound waves are NOT part of the electromagnetic spectrum.
The electromagnetic spectrum stretches
from radio waves at the lowest frequencies (longest wavelengths) at one
end (the relatively harmless end) through Infra Red (heat) waves,
visible light waves all the way up to Gamma Rays at the very shortest
wavelengths (highest frequencies) - the harmful end of the
spectrum. Gamma rays are harmful to human tissue and are produced
by events including the detonation of atomic bombs and from celestial
objects such as quasars.
||7.8µm - 3.9µm
|3Hz - 30GHz
THz - 10 THz
A Representation of the Whole of the Electromagnetic Spectrum
will concentrate on the relatively harmless end of the electromagnetic
spectrum - Radio Waves - which include Radio, Television and mobile
THE RADIO PORTION OF THE ELECTROMAGNETIC
Very Low Frequency
Very High Frequency
Ultra High Frequency
3kHz - 30kHz
30kHz to 300kHz
300kHz - 3.0 MHz
3.0MHz - 30MHz
30MHz - 300 MHz
300MHz - 3.0GHz
3.0GHz - 30GHz
types of use:
A Representation of
the RADIO portion The
The receiving device has to tune into the
required transmission and be able to reject all other transmitters
within range. This is done with a Tuned Circuit. The tuned
circuit acts as a Filter, without one all available broadcasts would be
received, which would be very confusing to the listener and quite
useless. The tuned circuit filters out the transmissions
that are not required.
If we look at the humble crystal set it
has a very simple tuned circuit consisting of a coil and a variable
capacitor. The size of the coil and the number of windings of
on it and the value of the variable capacitor determine which part of
the radio spectrum is received. The variable tuning capacitor
provides a convenient means of tuning to the required station.
illustration below shows the circuit diagram and the typical components
used. Once the tuned circuit has selected the frequency of the
required radio station it is passed on to the detector or diode
that will provide audio to the headphones.
Circuit diagram of a
Physical layout of a
In the case of AM radio the radio station firstly produces a radio
frequency carrier (the radio
wave) that is of constant average amplitude, this radio wave is modulated
with, and then carries,
audio frequencies of voice and music etc from the radio studio.
The modulation varies the amplitude of the carrier in response to the
frequency of the music or voices being transmitted - the sounds (audio)
is effectively superimposed onto the transmitted radio wave. This
Amplitude Modulation (AM).
Once the tuned circuit has tuned into the required radio station, if
the signal was fed straight to the earphone nothing would be heard
the earphone could not respond the very fast alternations of the radio
wave. Radio waves can alternate at frequencies of between
approximately 100,000 Hz and 100,000,000,000 Hz, whereas the sound
frequencies that we can hear and that an earphone or loudspeaker can
reproduce generally lie between 20Hz and 20,000Hz - quite a different frequency range!
The earphones have to reproduce the audio
frequencies that have been modulated onto the carrier wave at
transmitter. These audio frequencies are recovered by the electronic circuits of the
listener's radio receiver by using a 'detecto'r, often a Diode. The diode in the crystal set acts as a
rectifier, removing alternate half cycles of the radio carrier, so that
the resulting half waves will be in the same direction and the
detected audio frequencies cause the diaphragm of the earphone or the
cone of a loudspeaker to move in accordance to the average strength of
radio wave shown in the diagram on
the right is travelling from left to right at as constant and unvarying
speed of 300,000 kms (in space). The pattern of a wave is a
constant and repeating cycle.
The wavelength of the radio wave is measured as the distance between
two peaks of the wave. The frequency of a radio wave is measured
as the number of peaks that pass by a specific point (e.g. point X)
every second and is expressed in Hertz (Hz) after Heinrich Hertz.
Since the speed of a radio wave is always the same varying the
wavelength must also vary the frequency. If the wavelength
is increased the number of peaks that can pass point X must be lower so
the frequency of the radio wave will be lower. Conversely if the
wavelength is reduced the number of waves that can pass the single
must increase causing a higher frequency. The calculation to
convert a frequency to a wavelength is:
300,000,000 ÷ frequency (Hz) = wavelength(m)
300,000 ÷ frequency (kHz) = wavelength(m)
300 ÷ frequency (MHz) = wavelength(m)
The other consideration of a radio wave is the amount of energy that it
is carrying, this is the Amplitude, and is the height of the wave, as
seen in the diagram opposite.
Representation of an
unmodulated radio (carrier) wave
A Modulated Carrier
At the transmitter the audio from the
radio studio is modulated
the carrier wave. In the case of an AM radio transmitter the
frequency, and therefore the wavelength, remains constant.
of the sound alters the amplitude of
the radio wave, varying the amount of energy that the wave
carries. The audio signals that we want to hear are carried on
radio wave ready to be detected by the listener's crystal set diode or
detector on their transistor radio.
carrier wave is represented by the black line in the diagram on the
left, while the audio that is carried on it is represented by the red
line - the varying amplitude of the carrier wave.
^top of page
carrier wave of your favourite AM radio station, perhaps 'Classic Old',
is passed through the detector or diode and the resulting audio,
represented by the red line, is removed from the carrier and passed to
the earphones which convert the electrical signal to sound waves that
can then be heard. Magic!
The detected audio wave
|SOUND WAVES ARE
DIFFERENT TO RADIO WAVES
Bear in mind that sound itself is not transferred to our ears (or
to a microphone) by waves in the
electromagnetic spectrum. Sound waves are transferred by
vibrations in a
physical matter such as (normally) air molecules or other substance
perhaps through the vibrations of the molecules in wood, metal or
A high pitched sound has a higher frequency, and therefore shorter
wavelength, than a lower pitched sound which has a lower frequency and
therefore longer wavelength.
Sound waves cannot travel through space. Space is
a vacuum and thus has no physical matter with which to transfer
molecular vibrations. The only way we can hear sound through
if they are first modulated into a radio signal (by a microphone and
radio transmitter (in an environment that has an atmosphere that can
convey the sound to the microphone!)), - the radio signal is
transmitted across space and then received on a radio receiver which
then de-modulates the radio carrier wave so that sound can be
heard from the loudspeaker.
Physical sound waves that can be heard by the human ear are typically
at frequencies in the region of 20 hertz to 20,000 hertz (cycles per
second). The radio portion of the
electromagnetic spectrum (which is quite different to the sound
spectrum) ranges from about 3 hertz to about 300,000,000,000 hertz
(cycles per second); the
whole of the electromagnetic spectrum itself is vastly wider than this,
of course. Any SOUND wave can be piggy-backed onto a radio wave
means of modulation (e.g. Amplitude Modulation (AM), Frequency
Modulation (FM) or Single Side Band (SSB) for example) by using a radio
A READER'S QUESTION!
have just spent the last three hours reading and re reading your
on radio, it is a fantastic documentation and thank you for taking the
time to put together such an informative read.
My reason for emailing you is quite simple I am currently writing an
essay on radio, including both technological and sociological issues
both past and present. I have read your site several times and the main
thing that confuses me is information on broadcasting
frequencies/distances and formats.
I don't understand how they all relate to each other, for example
'Radio Four lost 206m (1457kHz) and 261m (1151 kHz) 'how do they
is the 'meterage', the distance they can transmit or the wavelength or
this the same thing, or is 206M the distance and 1457kHz the wave
length, if so how are these related. Also I presumed LW could be
transmitted further, but its seemed a lot of 'National BBC' programmes
were transmitted on MW, how is this possible. Also how does the power
a transmitter/radio mast come into the equation, does it transmit to
smaller masts which amplify the signal to get the coverage on MW and is
the higher the power the further it can transmit. You also commented on
early stereo transmission how was it possible as both local and
masts where used for each channel how can you tune to two stations at
once. How does FM come in all this as this seems to be the standard and
highest quality radio achievable now as early BBC broadcasts did not
Thank you for your time, I do hope you can help me out on these
questions, maybe I'm being stupid and the answers are just staring me in
I will do my best to answer, Lee:
A radio station is transmitted on a specific frequency within a given
defined 'wave-band'. For the general ANALOGUE broadcasting that
a talking about here, there are three domestic wavebands: 1/ Long
Wave 2/ Medium Wave 3/ VHF.
In Europe the authorities (co-ordinated by the the International
Telecommunications Union [ITU]) have allocated the domestic broadcast
radio stations space within the limited radio frequencies portion of
electromagnetic spectrum as follows:
Long Wave - occupies the part of the electromagnetic
spectrum stretching from a frequency of 148.5 Kilohertz to 283.5
[Note: 1 kilohertz
is one thousand cycles of a radio wave per second - referred to as
kilocycles per second from the 1920s to the 1970s when the term
kilohertz was more widely adopted. kilocycles per second is
abbreviated to kc/s : Remember that a radio wave is an alternating
electrical current constantly cycling from positive to negative and
again, and so on. An oscillation is simply the time it
takes for the voltage of the transmitter to go from + ve to - ve and
back again and is
expressed as the frequency.]
[Martin Watkins adds:- A transmitter is really just a
battery being whirled round and round between its terminals very
and that this can (and was) in the early days achieved by speeded up
Medium Wave - occupies the part of the
electromagnetic spectrum stretching from a frequency of 526.5 kilohertz
(kHz) to 1606.5 kilohertz
VHF (Very High Frequency) (Band II) Broadcast Band stretching
87.5 megahertz (MHz) to 108.0 MHz
[Note: 1 Megahertz
is one million cycles of a radio wave per second, previously referred
as megacycles per second. abbr. mc/s ]
DAB in the UK (Digital
Audio Broadcasting - or plain simple 'Digital Radio') - A small
part of radio spectrum stretching from around 209 MHz to 216 MHz.
Digital radio stations are broadcast is blocks or 'ensembles' called
"Multiplexes". Each single multiplex carries not just one radio
station, but a number of different stations depending on the level of
digital compression used. The higher the compression (i.e lower
bit-rates) the lower the quality of the audio will be, but the larger
the number of stations that can be accommodated into the
multiplex. Many areas in the UK can receive DAB radio and can
typically obtain three multiplexes: BBC National (all the BBC's
radio national stations - including Radio One, Two, Three, Four,
FiveLive, 6-Music, BBC 7, 1-Xtra etc), Commercial national Digital One (Classic,
Virgin, Talk Sport, OneWord, PrimeTime etc etc), Local (BBC Local Radio and
various commercial local stations). Some areas, especially around
London, can receive more local multiplexes or a regional multiplex,
whereas other areas receive fewer multiplexes (e.g. Northern Ireland
to lack of frequencies available). MORE
TELEVISION in the UK -
Currently both analogue 625 line colour broadcasts and digital
terrestrial television (DTT), in the form of "Freeview" and
use frequencies in the UHF (Ultra High Frequency) part of the radio
spectrum between 470MHz and 860MHz (known as Band IV and Band V). In other parts of
Europe and the world, Band I
(approx 46 MHz to 67 MHz) and Band III
(approx 175 to 210 MHz) are still used for television broadcasting.
Beyond The Broadcast Bands
Outside of these defined 'broadcast bands', the frequencies in between
are used for all manner of other communications - e.g. police, fire,
ambulance, boating and shipping, private 2 way radio, amateur radio
The methods of conveying the sound produced by the radio station vary
according to the band in question:
For the Medium Wave and Long Wave bands, it was
decided from the outset of radio broadcasting in the 1920s that the
method of modulating the radio wave would be AMPLITUDE
When the VHF band II was released for broadcasting in
1950's AMPLITUDE MODULATION was experimented with, but it was
decided to use FREQUENCY MODULATION (FM) as FM was found
to be somewhat less susceptible to some forms of interference - too
complex to go into here.
So you see 'FM' is not a 'band' and neither can 'AM' be
described as a 'band' - they are just methods of
the radio station output. FM could be used to broadcast
on Medium Wave or Long Wave (not that anyone would be able to hear it
an existing Medium Wave AM radio!) just as AM could have been used to
broadcast on the VHF broadcast band.
Now we come to the WAVELENGTH question -
A radio wave is an oscillating wave in the radio frequency portion of
the electromagnetic spectrum. The electromagnetic spectrum
stretches from the lowest frequencies at the 'radio' end of the
through the higher frequencies of 'sub-millimeter' ; 'Infra Red' (i.e.
Heat!); Visible Light; Ultra Violet; X-Rays (as used in hospitals) and
harmful 'Gamma Rays' (as emitted by fissile material and atomic bombs)
All these waves have one thing in common, they all travel at 300,000
kilometers per second (in free space) - commonly called the speed of
As all electromagnetic waves oscillate at a certain frequency to form a
wave of a certain length, the Wavelength and the Frequency relationship
is inextricable linked. Since the speed at which the wave travels
is fixed, at 300,000 km per second, if the frequency of the
is varied the only other variable that can change is the wavelength.
(Refer to Mr A Einstein for more detail)
The mathematical relationship between wavelength and
frequency is expressed in this fundamental and very important formula:
Wavelength (in meters) = 300,000 / Frequency (in kHz)
and also to put it another way:
Frequency (in kHz) = 300,000 / Wavelength (in meters)
SO: As the frequency of the wave is increased
the wave length decreases .
If we look again at the broadcast bands we can see the
relationship between frequency and wavelength:
Long Wave: 148.5 kHz to 283.5 kHz or expressed in
wavelengths as 2020 meters to 1058 meters.
Medium Wave: Frequencies from 526.5 kHz to 1606.5
kHz or expressed in wavelengths as 570 meters to 187 meters.
Wavelengths in Meters were always quoted by radio stations and marked
on radio dials until the 1980s when frequencies were more generally
adopted as the method of expressing where the particular station
appeared on the radio dial.
VHF radio has always used mc/s or MHz to express the position on the
dial, but just for clarification here are the meter values too!
VHF: Frequencies from 87.5 MHz to 108.0
MHz could be expressed as 3.428 meters to 2.778 meters (but
in reality the expression of meters is never used on air).
Now look at a practical example:
Many years ago Radio Four lost the use of 1457 kHz
frequency. But when that happened radios were marked in
Meters, so what was the wavelength of that transmission?
Take 300,000 and divide it by 1457 and you will get an
answer of 205.90 Meters.
This is rounded up for simplicity when being quoted on the air by
presenters as 206m . Simple!
The fact that a radio station, such as BBC Radio Four from the 198 kHz
Droitwich transmitter has such a very long wavelength means that for
each cycle of oscillation of the radio wave it must travel 1515 Meters.
Compare that to Capital Gold Radio on 1548 kHz medium wave this has a
much shorter wavelength, and the wave only travels 194 meters per cycle.
Very simply put, for a given and equal transmitter power, for each
cycle of the radio wave the BBC Radio Four 1515 m transmission covers a
much bigger area than the shorter wavelengths used by Capital Gold
on 194 m. Shorter wavelengths are absorbed and attenuated
(reduced in intensity) more quickly and therefore cannot cover such a
large area for a given transmitter power.
This effect explains why BBC Radio Four only requires 3 main long wave
transmitters on 198 kHz to cover virtually the whole of the UK, while
BBC Radio Five Live needs 10 main medium wave transmitters to obtain
near national coverage.* The
longer waves of BBC Radio Four at 1515 meters are absorbed and
attenuated to a much lesser degree than those of BBC Radio Five Live
using medium wavelengths, which are absorbed to a greater degree which
causes the signal to fall off more rapidly with distance from the
adds: It's not an exact analogy, but the bass drum of a brass band
playing in the distance will be heard more clearly than the piccolos or
fluegel horn. As I say it's not an exact analogy with LW/MW
attenuation, but HF sounds are screened by obstacles more than LF,
explained at least in part by their wavelength, and by absorption in
[ * BBC
Radio Four also uses 9 filler transmitters on medium wave, while BBC
Radio Five Live also uses an additional 13 medium wave filler
Certainly the relationship
between power and distance is important. The more energy that is
put into the radio wave the further away it will provide an effective
listenable signal. This in exactly the same way as using a higher
power light bulb will be more more effective and be seen further away
compared to a lower wattage bulb. (Of course light is part of the
electromagnetic spectrum to which radio waves belong). A 150
light bulb will, for example, be much brighter and therefore be seen
further away than a 25 Watt bulb.
It is also interesting to note that doubling the transmitter power does
not double the distance that the transmitter will cover. To
the signal strength at the listener's radio receiver aerial a power
increase of 4 would be needed!
For a radio aerial (either transmitting or receiving) to have maximum
effect it must be of a resonant length compared to the radio frequency
that it is transmitting (or receiving, of course). For a long
station a very tall aerial is required to be able to resonate
effectively at those wavelengths. Long Wave = long wavelength =
long or tall aerial.
For medium wave the wavelengths are obviously shorter than long wave so
a shorter aerial is required.
Many medium and long wave stations simply use a tall metal mast as the
aerial, the height of which will vary depending upon the wavelength of
the service being transmitted, but will be many tens of meters in
For VHF (or if you must call it FM) broadcasting the aerials are going
to be much smaller, only a few meters across, and these will be
to the top a tall masts or towers to gain height advantage.
In the early days the BBC experimented with Stereo broadcasts.
Stereo requires two AUDIO
channels; (simply put) one to carry the sounds from the right hand
microphone channel and the other transmitter to carry the sounds from
the left hand microphone channel.
The only way to do this in the 1920's was to use two radio transmitters
on separate frequencies. In this early stereophonic experiment
right hand audio channel was transmitted over the BBC long wave
transmitter, which covered most of the country, while the left hand
channel was simultaneously transmitted over the BBC's numerous local
medium wave transmitters.
For listeners lucky enough to have two radios, they could tune one into
long wave and place it on the right of the room while the other was
tuned to medium wave and placed on the left hand side of the
By sitting in between the two radios the listener could get a sense of
the space and ambiance and stereo sound-stage that we all take for
In the 1960's stereophonic transmissions were introduced to the VHF
(FM) radio services of the BBC. This time, however a new system
had been developed, called the Zenith GE Pilot Tone system
(developed by General Electric of America) that did not require a
separate transmitter and radio for each audio channel. The new
system used the existing VHF frequency of the BBC station and added
(Coded) in the extra components in the form of a 'multiplex' on top of
the existing radio signal. The idea was that the system would be
compatible with existing mono radio sets, which would continue to
receive the programmes unaffected and as normal in mono of course, but
new radio receivers would be available that were fitted with the
Decoders required to extract the multiplexed stereo components
and reproduce a stereo signal that would be fed to twin speakers via a
stereo hi-fi amplifier. The Zenith GE Pilot Tone System is still
used today on the VHF/FM band. Incidentally the Pilot Tone is an
almost inaudible audio tone of 19kHz that is transmitted along
with the sound of the radio station, when a suitably equipped radio
'hears' this tone, it switches on the stereo decoder circuit so that
stereo programme can be resolved and heard.
(Incidentally, the 19kHz audio tone should then be stripped from the
recovered audio by a special and very steep audio filter before it
reaches the audio amplifier stage, however some poorly designed (read
cheap) radio tuners do not do this effectively and people with very
acute hearing can sometimes still hear the high pitched whistle!)
Hope this answers your question in some small way.
I'm a faculty member
in the MIS department at Temple University (Philadelphia, Pa.).
One of the courses I teach is the introduction to networking.
You're page on radio info is great! I may direct some of my
students to this page to get a better understanding of the various uses
of each range of frequencies in the RF spectrum.
Here is one additional
question for you. Do you know where I can find information
regarding the RF spectrum that explains other things about the various
bands such as the type of range you can expect from each band, the data
rates you might expect, the things that cause the most interference,
Thank you for your-mail and your kind comments. I don't pretend to be a
radio engineer, or particular expert, but I have presented the
information on my website as useful material that I have previously
researched and used in my own hobby of radio. I hoped that others would
find this useful, as I have done, and I am glad that you have too,
As for your other questions, I don't immediately have a reference that
may answer them. However I do have a number of friends 'in the know, so
I will ask them for you.
In simple terms, for local ground wave contacts, the longer the
wavelength (the lower the frequency) the further the signal will travel
- for an antenna of given efficiency. In Europe we still use Long Waves
(150 kHz to 300 kHz) for the transmission of AM radio stations. This
means that during daylight in ground-wave conditions (night-time is
different due to sky-wave reflections) long wave stations in France and
Germany are quite audible here in the UK. Also the 198 kHz
transmissions from the BBC are very popular across north west Europe.
This means that the whole of the UK can be covered with just three long
wave transmitters using a single frequency (albeit that a few
additional medium wave transmitters a required to fill in the 'mush
zones' where the co-channel transmissions overlap and interact).
Contrast this with the national medium wave (medium frequency, AM,
500kHz to1700 kHz) network that requires perhaps a couple of dozen
transmitter to cover the UK and the or more, and the VHF (very high
frequency 'FM', 88 MHz to 108 MHz) network that requires hundreds of
transmitters to cover the UK (this is because VHF and UHF radio waves
are very much line-of-sight. Medium wave and long wave signals tend to
hug the earth more - following its curvature.)
If we have a look a high frequencies (HF, short waves) then these are
locally quite short range, useful for short range local contacts like
CB radio, so it may seem odd that short waves are so popular for
international 'world band' broadcasting. However short waves are
readily reflected off the ionosphere in the earth's upper atmosphere.
In fact short wave can travel all the way around the earth by multiple
bounces off the ionosphere and the earth's surface.
Medium wave radio waves are also subject to a similar effect during the
hours of darkness when the ionosphere is able to reflect them,
therefore allowing MW signals to travel a greater distance. VHF and UHF
can also be reflected great distances but under a different and
unpredictable effect known as "Sporadic E" - reflections off the E
layer of the atmosphere.
A consideration for general domestic use is aerial efficiency.
The longer the wavelength the longer the aerial required to work
efficiently. As a rule of thumb a 1/4 wave aerial is a fair compromise
for a reasonable efficient aerial system. This means that for a VHF
(FM) transmitter using, say, 98 MHz a 1/4 wave ground-plane aerial
would be about 0.76 meters long. That's quite easy to accommodate. If
you decided to use, say, 1000 kilohertz medium wave, then your 1/4 wave
monopole radiator would be 75 meters high. If you decided to use a long
wave transmission on 200 kilohertz, then your 1/4 wave monopole
radiator would be 375 meters high! (In practice professional broadcast
transmission engineers use clever techniques such as loading a shorter
aerial so that it appears electrically longer to the transmitter. One
must also bear in mind that even though a VHF aerial, used for FM
radio, is quite small, it must be mounted very high up so that it has a
good 'view' of the horizon. So the masts used for both medium wave and
VHF broadcasting might very end up being of very similar height
Aerial efficiency can play an important part in local communications.
Here in Europe we can use (as I do myself) Citizens Band (CB)
Radio at 27 MHz (high frequency, short waves), or PMR 446 (446 MHz,
UHF) walkie talkies for short range two way communications. A CB radio
uses a 4 watt transmitter and a PMR 446 radio uses a 0.5 watt
transmitter. Given an efficient matched aerial of correct length (about
3 meters long for CB and 16 centimeters long for PMR446) CB Radio can
cover about 5 miles and PMR446 about 1 or 1.5 miles. However when using
hand held walkie-talkies with a need to use small easy to handle
aerials it may be found that PMR446 has as good, if not better range
than a CB Radio. This is because the aerial on a PMR446 radio is
very short anyway and thus easy to handle and will be the correct
length for good efficiency. However an aerial on a CB radio would need
to be a couple of meters long for proper efficiency - not conducive to
easy handling (!) - so often a short "Rubber Duck" aerial might be used
that is only a foot or so long. This reduces transmit and receive
efficiency considerably, so much so that it may be that the 0.5 watt
transmitter used by the PMR446 radio into an aerial of the correct
length will be much more effective than a CB radio using 4 watts into
an antenna of the incorrect length.
As for frequency, it is my understanding that the higher the frequency,
i.e .increased cycles per second, the rate at which data packets can be
transmitted can be increased. I imagine that this is why ultra high
frequencies of 2400 and 5000 MHz are used for wireless routers and
access points used in Wi-Fi networks.
I hope this is of interest.
I will try to come back to you with more as I have it.
I have been reading your
wonderfully informative web site about radio. To the layman like me you
have really opened the subject up and educated me- that's got to be an
Anyway, I am wondering if
you can help me with a query. I am a falconer in the UK and I use radio
tracking equipment to recover my hawk if ever it is temporarily lost
from view. The telemetry systems available in the UK operate on either
173.225 MHz, 216 MHz or 433MHz. As far as I am aware the only legal
telemetry frequencies for this kind of use in the UK operate on the
173.225 and 433 MHz frequencies which means that 216 MHz is illegal.
However, because telemetry in falconry is a fairly recent innovation
the first equipment available was on 173.225. This had a drawback
because the antennas on the transmitters were a bit too long and when
attached to the hawk would on occasion snag on wire fences or other
obstacles pulling feathers out or worse still electrocuting the hawk if
it landed on a power pole. When equipment on 216 became available
shortly afterwards (late 1980's) many falconers switched to because the
antennas were shorter and to protect their valuable hawks. Most did
this oblivious (or dismissive) of the law. Since then manufacturers
have begun offering equipment on 433 MHz but it has been slow to catch
on particularly as so many had already got receivers and transmitters
on the two other frequencies. A situation has now developed with
the potential advancement of digital radio and there is a rumour in the
falconry world that DAB may soon begin transmitting on 216MHz.
Falconers with 216 equipment are worried understandably because they
may have to fork out for new receivers and transmitters - the former
are about £400 each and the transmitters about £100.
Firstly do you know if DAB will be transmitted on 216MHz and if so will
it affect the falconers analogue receivers? The obvious answer is that
falconers on 216 should switch to legal frequencies I know but for now
any help you could offer would be really helpful.
Thank you for your e-mail and your kind comments. You raise some interesting issues.
The reason that the use of 216 MHz (or any other un-authorised
frequency) is illegal is that the particular frequency in question will
have bee marked by the government and Ofcom for a specific use, either
now or in the future.
The illegal use of such frequency by low powered transponders may
not currently cause undue interference to legitimate and licensed
users, especially if the frequency allocation is used by only a small
number of legal transmitters.
However 216 MHz has always fallen inside the legitimate 174 to 230 MHz
'sub-band' allocated by Ofcom to DAB radio. Ofcom are now in the
process of expanding this band further, and as part of that process a
new national network of about 170 high power DAB transmitters is due to
be installed from next year (2008) onwards. This will use Block 11A -
i.e. 216.978 MHz - in the DAB sub-band within VHF Band III.
Although I don't think that there is an allocation as yet, there is the
possibility that Block 10D may also be used at some time, this is at a
frequency of 215.072 MHz - just on the other side of 216 MHz.
I cannot say for certain if these DAB allocations will cause the users
of illegal transponders problems, but I would think that there may be a
chance that their reception would be 'wiped out'. Digital transmissions
would appear simply sound like the "Hiss" of a de-tuned radio, so it's
difficult to tell if you are receiving anything on an analogue radio.
However these DAB signals will be quite strong and may be enough to
make the very weak signals from the transponders un-readable.
All I can advise is be prepared for the worse. See what happens.
At least the legal 433 MHz equipment will use even smaller aerials!
I hope that helps.
Your response has been the most detailed and factual yet. This
information is exactly the news I was searching for. I am so very
grateful. The only thing is, now that I am equipped with this knowledge
I now have more work to do!
Once again so many thanks.
PS. Still not had a reply from Ofcom on any of these topics.
HF Series Receivers
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