1 Advisory note on broadcasting on the South Coast

1.1 Introduction

2.1 Increase Power

2.2 Using an In-fill transmitter

2.3 In-fill transmitter (the "GROUP H" idea)

2.4 Exchanging Frequencies

2.5 Changing the transmission type

2.6 Educating the Listener

3 Further Information and Clarification

4 References & Bibliography

1 Advisory note on Broadcasting on the South Coast

The reader of this document should be aware that whilst all of these solutions listed below work in practice a number of them are invalidated due to the restrictions on broadcasting on the South Coast. This is related particularly to the interference caused to French based reception but generally reception on the continent as a whole.

The reader should also note that a number of transmitters are set up in a particular fashion to deflect the majority of the power away from the French (and hence also the Southern points of land). In many cases a compromise is reached where the solutions provided may be carried out but not to their full extent. In writing this document I have attempted to provide a number of solutions. This is in the hope that at least one of them will not be blocked by the authorities (U.K or European) and hopefully this will successfully carry out the function for which it is desired to perform – to improve the coverage of Capital Gold. It should be noted that the M.F. (medium Frequency or Medium wave band), has a large number of broadcasters particularly close to one another and as the number of stations steadily increases the problem will only worsen. It was this that coursed the 1978 European frequency reshuffle.

1.1 Introduction

Capital Gold off the Brighton transmitter (located at Southwick) is a 0.5 k W (Estimated Monopole Radiated Power - often abbreviated to EMRP) signal. However at night (but particularly in the winter) the station suffers from co-channel interference and adjacent channel interference from foreign-based transmitters.

Unfortunately this is due to the nature of the movement of the Ionosphere. This has 4 main layers, D, E1, F1 & F2.

"…Because these layers are generated by the sun’s activities the lower layers (of the Ionosphere) are in place only during the day; at night the Ionisation disperses and there are no free electrons"

"…the movement of the Ionosphere can be express using Snell’s law of refraction - n_o sin θ₀ = n1 sin θ₁" ^[1] [page 237/8]

Clearly the interference caused to Capital Gold will also be comparable to the interference Capital Gold itself causes to the other foreign stations in their traditional coverage areas – due to the angle of incidence being the same!

So the solution to this problem is not a simple one – we can not simply add in some additional overseas based transmitters which carry Capital Gold programmes to the area of the U.K that is worst effected by sky wave propagation. Mainly because it only compounds the problem somewhere else but also there is quite a serious phase problem;

"Under selective fading, different frequencies of a signal will arrive at the receiver having undergone different amounts of propagation delay…" ^[1][page 198]

Capital Gold (off 1323kHz – at Southwick) does seem to be the worst effected of all of the stations with transmissions off the Southwick mast. In winter selective fading begins at Hove – just 4 miles from the mast. This increases more and more and throughout Central Brighton itself the signal is unlistenable. Once the viaduct at Brighton is in sight the signal degrades rapidly and this would be a major put off – especially in winter when it is at its worst. It is also a known fact that all M.F based signals do not propagate well into cities anyway. There are also serious phase issues up most of the Lewes Road and generally through winter the sound is quite poor in this area.

Fortunately 945kHz (Bexhill) is O.K in Brighton although suffers phase problems - this too is at times quite badly disrupted by foreign-based transmissions.

Looking at competitors, Virgin uses 1197kHz at a power of 1.1 k W, this signal does not seem to suffer too badly from propagated signals although French and Spanish signals appear to cause problems particularly in Central Brighton and up the Lewes Road which makes it unlistenable in Falmer. Most of this is compounded by the fact that most car receivers (generally) are on the move (!) and at an angle of 45^o! However, this signal seems to get further than 1323kHz before problems arise.

Talk Sport on the other hand uses 1053 kHz but at a power of 2.2kW, Talk Sport has no problems with coverage of Brighton bar a small area around the station where the tracks themselves course electrical interference.

Figures from the radio authority – clearly showing the powers used ^[2]

Therefore it can be deduced that increasing the power well cause an improvement upon the quality of the received signal. A power of approximately 1.3kW would mean coverage for most of Brighton throughout the year. 1.1 kW would work although it may have problems around the Lewes Road area which is a valley. On the side of this valley facing the transmitter is a large hill which leads up to Ditchling Beacon (the highest point in Sussex) this blocks the signal to Lewes Road.

Here an old map of what was BBC Radio Sussex indicates the reception achieved by using 1kW (Shoreham is a less accurate way of describing the site at Southwick). The reader should note that the daytime coverage extends from Lewes to Burgess Hill. This I feel is inaccurate, and that the Capital Gold signal in particular extends further than these points during the daytime. Since 1485kHz is further up the band than 1323kHz, the propagation at the top end of MF is not as good as it is at the lower end hence the higher ERMP but for pretty much the same result.

It should be noted that all transmissions from Southwick have to cross a power transmission line (providing electricity) – this weakens the signal strength. A number of hills in the region also affect the strength of the signal.

[3]

A coefficient could be used to multiply the statistical data achieved to get a more accurate figure of reception at the various points – but this would be pointless because many receiver designers have improved their products and hence are more sensitive and selective nowadays!

It would be nice to have radios available at price of around £100 or less which have Q factor (also known as quality factor) of around 9. However, many for that price have a Q factor of close to 30 and also suffer from poor receiver design where the Intermediate Frequency (I.F), are badly chosen.

This is the most obvious solution to the problem, although due to restrictions may not be suitable.

2.2 Using an In-fill transmitter (on a new frequency)

If it is not possible to increase the power it may be possible to use an in-fill transmitter on the worst affected parts, ideally this transmitter should use another frequency (although that does not have to be the case – see below!).

Using a new location would not be an advisable issue since a new Medium Wave site cost over £100,000!! – So therefore a current transmitter must be used and an additional aerial added to it. There are no other Amplitude Modulating transmitters available in Brighton – the next nearest is Duxhurst or Bexhill. Duxhurst is an option but means a very large over lap especially with 1548 (London), 1323 (Brighton) and this new Duxhurst frequency. So a closer transmitter must be found.

There are a number of television transmitters in the areas worst effected which may allow for an aerial to be added (perhaps more of a sloping wire would be a better idea). A prime transmitter for this is the Bevendean Television transmitter that lies above the valley of Moulscoombe and Bevendean an area badly affected after dark.

Another option is using the Whitehawk Hill transmitter and again using a sloping wire.

This however has its problems,

"MF antenna's suspended from a TV mast have never worked. If you have access to a Tektronix VM700, look at the baseband output of any of the TV services from Crystal Palace and you can see carriers at approx 558 kHz, 720 kHz, 1035 kHz which is the MF signal getting into the video circuits on the transmitters CP. All sites which run such MF antennas suspended from a TV mast, reception is usually marginal at best." ^[4]

Hence this would add in a carrier at 1323kHz or another frequency used for the in-fill would cause a signal to get into the video circuits (as in like above). Since Bevendean is a very marginal area for television reception this may not be the best of plans and may push reception down even more for television watchers in the area.

A third idea is to make use of the University of Sussex’s transmitter at Falmer, currently using 1431kHz and a power of just one Watt(!!), to broadcast student radio to the campus. It does however just carry down the Lewes Road and just down to the University of Brighton’s Campus at Moulscoombe, which is about 2 miles away.

Capital Gold could use this mast with a power of say around 40 to 100 Watts since this is close to the area which is worst affected then this is an option. Clearly to broadcast at any of these a licence may be required.

Barring this a sloping wire approach again could be used between the Cockroft building and Watts Building of the University of Brighton – this would be far from ideal though as its right in the middle of the valley!

^[3]

– the Lots Road Power station, used originally for broadcasts of Capital Radio, before the M.F array at Barnet was constructed. The arrow indicates the transmitting wire. Picture © Phillip Rayner.

If it is not possible to have an additional frequency to use as an infill transmitter, Then it may be possible to use an age-old idea dating back to the 2^nd World War. This idea allowed the continuation of radio without making the transmitters themselves a target for the Luftwaffe and its Radio Direction Finding (RDF).

"Group H … consisted of 61 transmitters, with an output of 50-100W in towns having a population of 50,000 or more. All operated on 1474kc/s and were, if possible, built adjacent to a tall structure (water tower, chimney etc) so that conventional masts were rarely used to support the wire aerials." ^[3]

During the war this worked successfully using a very simplistic method of audio tones and mathematics, and with rapco standards these days it may well be possible to be accurate to less than 1Hz!

"The frequencies of all the MF stations had to be maintained within very fine limits to prevent beats with nearby stations. A system of audio tones derived from the group "Master" frequency, was line fed to all the group, multiplied, then compared with the station output. Drives were then adjusted for zero beat. Later, in 1943, a single 1kc/s tone was distributed to all stations from a master crystal oscillator in BH and applied to a CRT for a visual display of the frequency error." ^[3]

(BH being an abbreviation for (BBC) Broadcasting House London.)

– Whilst this worked with 61 transmitters during the war, Capital Group need only need two or three transmitters just enough to cover the target area. So this idea may work – just on a far smaller area.

2.4 Exchanging Frequencies

Exchanging Frequencies may well work for Capital Gold but someone is most certainly going to lose out!, Talk Sport’s 1053Khz frequency carries well all across Brighton, 1485 is OK, although not brilliant, like wise Virgin (on 1197kHz). If one of the other stations are mad enough then Capital could swap its mediocre 1323 frequency for one of the others (1053 would be the best choice). This however is far fetched and is highly unlikely. Especially as the nation-wide stations have these frequencies nationally! Virgin re use 1197, 9 times, and Talk Sport re use 1053, 13 times. Hence interference could result from the other transmitters in the country under skip conditions.

2.5 Changing transmission type

The current system of Amplitude Modulation transmissions is wasteful since a large amount of the power is wasted in the carrier. Single Sideband transmission is a much better way of transmitting the signal.

"SSB has only one Sideband, which is demodulated using a local generated carrier. The effect of selective fading is therefore greatly reduced" ^[1] [p.198]

Also the power is transmitted across less of bandwidth and hence less power is required.

The Motorola QU-AM system could be used but making any changes like this moronic.

2.6 Educating the Listener

No matter how hard any engineer tries to improve the reception and transmission of any Amplitude Modulated broadcast it is a loosing battle, this is especially true with so many restrictions on broadcasting on the South Coast. However, as of January 2004, Digital Radio (DAB), will be present of the Brighton (Whitehawk Hill) mast. This Multiplex will include Capital Gold in stereo; this is advantageous for a number of reasons and listeners where possible should be directed onto this far superior media. As was the case in 1978 when listeners were being directed on VHF (as it was then correctly known). DAB being the next step forward especially as it is not effected at all by night-time interference and coverage should be seamless especially in the Primary protected area. This unfortunately may be the only solution, which is viable.

3. References & Bibliography

The following sources have been used for information regarding this design idea;

• 1 - Telecommunications Engineering Principles, 3^rd edition, Dunlop, J and Smith D.G, Stanley Thomas Publishers, ISBN 0-7487–4044-9

• 2- The Radio authority - http://www.radio.gov.uk

• 3 - Mike Brown’s transmitter gallery at [www.mb21.co.uk]

• Audio & Hifi Handbook, (Revised 3rd Edition), Sinclair, Ian R Sinclair, Newnes Publishing. ISBN 0-7506-4975-5

• The radio now web site
www.radio-now.co.uk]

• Microsoft World Atlas 1998 Edition