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Rowridge TV transmitter, or, to be more accurate, transmitters, because in 2010 a second mast was built in connection with the digital switchover. The new mast (at 187m) high is taller than the old one.              Picture : R Tapper

External Links


Rowridge Page at MB21

Rowridge Page at The Big Tower       

Rowridge Page on Wikipedia


Digital UK Rowridge transmitter

Digital UK details of Meridian transmitters

Ofcom details of Meridian transmitters

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Rowridge transmitter`s channels in relation to the TV band and the gain curves of the aerials we recommend for it.   DM Log    Log36    Yagi18A    XB10A    XB16A


Also see other relevant A group curves and Rowridge co-channel problems.

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Wrong aerial for Rowridge 2 Wrong aerial for Rowridge 1

These are the wrong aerials for Rowridge (or any other A group transmitter).    

(see Rowridge Graph)

Both these aerials are actually on Crystal Palace transmitter but because it`s an A group (just like Rowridge) the article is just as relevant for this page.

The installations were spotted in Purley On Thames, just West of Reading, which is about 40 miles from Crystal Palace. The thing is, they`re the wrong aerials for Crystal Palace, or any A group transmitter come to that.

I`m not familiar with the signal strength in this location (though the one on the left was on

a bleedin` high pole....) but whether it`s a strong or weak area the installer has still fitted

the wrong aerial.

Why ?

Well if it`s a weak reception area an A group aerial should have been used.

On the other hand if it`s a strong or medium reception area he should have

fitted a Log Periodic aerial,


Let`s assume it`s a weak area. I estimate that over the Rowridge frequencies the

aerial on the left would average about 1.5 dB more than a DM Log and the one on the right about 2.0 dB more. But if you`re short of signal a Yagi18A would give about 4.7 dB more, and an XB16A about 6.5 dB more. We had a customer who was shielded from Crystal Palace transmitter by the Arsenal football stadium. He originally had a DAT75 A large wideband Tri Boom aerial) but his pictures were very poor, so he swapped to an XB16A and reported that whilst his signal wasn`t perfect it was much better, “we can actually watch TV now” was his exact comment !  QED #1


Now don`t get me wrong, I`m not saying these wideband aerials aren`t working for these particular installations. Let`s be honest, if it`s a decent signal area they`ll work fine.

But the fact is that on Rowridge there would be a minimal performance difference between one of these huge wideband aerials and a Log36. The latter performs just as well (in the A group) as any wideband Tri Boom antenna, yet has much less wind loading, it`s still a wideband and has all the advantages that a Log Periodic aerial offers.  QED #2


The thing is a Log36 is smaller than a Tri Boom so some installers find it harder to justify their (large ? ) bills.....   Any connection ?  Or am I just getting cynical as I get older ?


In my opinion if any installer tries to sell you this type of Tri Boom aerial for Rowridge

(or any other A group transmitter) you can quote me that he’s fitting the wrong antenna.


Although I think Tri Booms are over rated (particularly for frequencies at the bottom of the band) it`s possibly a little unfair to pick on them because all of the comments in this article apply (to a large extent) to any wideband Yagi type aerial, whether X Beam or not.

But all Tri Booms are wideband so at least I can be sure what I`ve photographed !   


See this customer Aerial Report.

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High gain aerial can reduce co-channel interference Low gain aerials can make co-channel interference worse

Above we have two graphics illustrating co-channel problems. The top one shows the kind of acceptance angle you`d get with a "low  gain" aerial, whereas the bottom one shows the same but with a "high gain" aerial. Note how the the acceptance angle is narrower on the "high gain"  aerial, that`s why it`s a high gain aerial !  (see Polar Response Diagrams).

The reason the high gain aerial is in red is to represent an A group antenna, which is the one you should use with Rowridge, which is an A group TX ! Therefore a Yagi18A, an XB10A or (ultimately) an XB16A would be a good choice.


If the offending transmissions are coming from behind  try using an aerial with a high rejection of signals from the rear, i.e. a Log Periodic or, particularly, a Grid. Alternatively try to site the aerial where it`s shielded from the miscreant transmissions, e.g. down the side of your house or on the other side of the chimney.


If the unwanted transmitter is to the side of the alignment onto the required TX, the first option is to try and resite aerial so it`s shielded from the unwanted transmissions, see above,

The next option is the use of an attenuator to try, in the case of digital, and tip the unwanted transmissions down the cliff edge whilst leaving the wanted ones at the top. The setting of the attenuator may need altering under different weather conditions. Note that an attenuator on its own cannot increase the difference in the signal levels received from each transmitter, it can only reduce both signal levels equally. Thus an attenuator works best in conjunction with  a high gain aerial  (even if already in a strong signal area) to increase the difference in the signal levels from each transmitter. If we say, just for the sake of argument, that the unwanted transmissions are being received at 0dBd (which is not  zero signal remember, it`s just the amount of signal collected by a dipole on its own) the difference between our low and high gain aerials [in the above graphic] would be 12dBd to 6dBd. That is to say that the difference in the signal levels (between the wanted and unwanted transmissions) from the high gain aerial would be 6dB more than from the low gain one. And that`s a big difference.

Most of the above also applies if the rogue transmitter is directly behind your aerial (see section above).

Variable attenuator.

If the transgressing transmitter is directly in line with the wanted one, you`ve got big problems. The only thing you can do is experiment with an attenuator though this is an even longer shot than with an off line pair of transmitters. Remember the setting of it may need altering under different weather conditions.


But, is there a different transmitter you can use !



If the unwanted transmitter is just "off beam" of the wanted one you`ve more of a chance of minimising co-channel then if it`s directly behind.  The use of an attenuator, usually in conjunction with a "high gain" aerial, is the way to go, see above. As the graphics above show a high gain aerial with its narrow beam width is less likely to pick up the unwanted transmissions than a "low gain" aerial with its wider acceptance angle.

You can also try aligning your aerial slightly to one side of the required transmitter in an attempt to avoid the unwanted broadcasts, this has more chance of working if your antenna is a high gain one. If it makes no difference one way, try the other way !  You could even try altering the tilt of the aerial. There`s no particular reason why this should work but RF is a Black Art, if you`re desperate you should try anything. What have you got to lose, apart from your time, or sanity.

As Bill Wright would say, "proceed empirically" a posh way of saying forget theory, it`s what actually works that counts, suck it and see.

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Above are the French Transmitters that tend to give the most co-channel interference problems with UK TV transmitters, as advised by Ofcom.   

Post switchover Rowridge will (uniquely) be transmitting in vertical as well as horizontal polarity in order to lessen the chances of co-channel interference. The aim is to give people the option to use either polarity and therefore take advantage of cross polar rejection to help reject the unwanted transmissions.    

Further details of their frequencies digital transmissions can be found by clicking on the link.

Can`t read French ? Try using Google Translate, French to English obviously !

The numbers in red are other UK transmitters which can also be affected by co-channel interference from French broadcasts :

Transmitters most likely to cause co-channel interference with Rowridge

1   Crystal Palace

2   Bluebell Hill

3   Dover

4   Heathfield

5   Midhurst

6   Hannington

7   Stockland Hill

8   Beacon Hill

9   Caradon Hill

10  Mendip

If you receive your signal from Rowridge and suffer from co-channel interference try polarising your aerial vertically.


Below is a Channel Allocation Guide for the French Transmitters most likely to give co-channel problems with UK broadcasts, namely, Brest, Rennes, Cherbourg, Caen, Le Harvre, Rouen, Neufchatel, Abbeville, Lille, Boulogne and Dunkerque.

The information was correct as of November 2011. The links to the French sites (above) should be accurate.   (Thanks to Martin Watkins for researching the information here).

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How To Combat Co-Channel Interference


Co-Channel interference is when your aerial picks up two transmitters (TXs) both broadcasting on the same frequency and it is never something any aerial installer welcomes.....  The transmissions can both be from within the UK just as much as they can be from abroad, and the latter is what those on Rowridge TX can suffer from, particularly under high pressure conditions, also known as "lift" conditions. In general these conditions have the most effect at lower UHF frequencies so group A will tend to be affected more than group CD. Radio is even more affected because the frequencies are even lower, particularly when one gets down to MW. The map below shows the location of the major sources of co-channel from French transmitters, though there are of course more transmitters further North in Belgium and Holland. Many other locations can suffer from co-channel from continental broadcasts if their aerials face South or East, even homes in Sheffield (which is in the middle of England ! ) can get continental co-channel if they`re aligned onto Belmont, i.e. their aerials face East. Bear in mind that the nearest country (East) past Belmont is about 200 miles past it ! !


When UHF TV started in this country the transmission planners did their best to minimise co-channel interference by assigning different groups to adjacent main transmitters, though, of course, the main reason for this was to allow the use of more efficient grouped aerials. To take Emley Moor (a B group) as an example, the four nearest transmitters were Bilsdale (A group), Waltham (C/D group), Belmont (A group) and Winter Hill (which is admittedly on the other side of the Pennines. a C/D group. If TXs of the same group had overlapping coverage areas then the broadcast frequencies would be chosen to avoid co-channel, see the Channel Allocation Guide.

Differing transmission polarities are also used to try and minimise problems from co-channel, and Rowridge transmits both polarities to give people the option to minimise co-channel.


Bear in mind that a vertically polarised aerial will be more susceptible to picking up off beam transmissions (the main cause of ghosting and co-channel interference) because to a certain extent, to those broadcasts from the side the antenna is effectively a vertical dipole.  


Let me be quite honest here, co-channel interference can be a pig to solve. All the techniques advocated here are correct in theory, but RF is a Black Art. They may work, they may not.....


There are three main weapons in the fight against co-channel, aerial positioning, attenuators and "high gain aerials", particularly (if it`s possible to use one) a grouped aerial . The latter two would usually be utilised, somewhat bizarrely, together. This is because an attenuator on its own cannot increase the difference in the signal levels received from each transmitter, the ratio between the wanted and unwanted signal levels will stay the same. There isn`t much reason, theoretically, why an attenuator would work on its own, but it does work sometimes, and because they`re cheap and easy to try I`d always give it a go. They`re more likely to be effective under "lift" conditions (i.e. high pressure) when the level of all the received signals has risen, and thus it may also be causing cross modulation interference in the tuner (and/or amp). What we`re always trying to do is increase the amount of signal collected from the required transmitter, whilst reducing the amount from the unwanted transmitter. An amplifier is not what`s wanted at all, since it`d amplify both transmitters equally, in fact it would probably make things worse, particularly if the site is in a strong signal area.....

Rowridge Transmitter


OS Grid Ref SZ 447 865


Note, due to the new phenomenon of MUXICAL chairs you may experience problems with certain MUXES disappearing. First try rescanning your TV / set top box, do it manually if possible. If this fails to sort it check on transmitter work or call the reception advice phone numbers.


Also see basic digital fault finding.


Switchover at Rowridge occurred in April 2012)


The wrong aerial for Rowridge

Rowridge transmitter was constructed in 1966 for the broadcast of BBC2 in UHF and BBC1 / ITV were added in 1969. The mast is situated 3 miles SW of Newport on the Isle of Wight, that`s about 15 miles due South of Southampton.

The original structure is a stayed spaceframe mast with a height of 150m (to the top of the shroud covering the transmitters) and it has an average aerial height of 280m. However in 2010 a taller mast (187m to the top of the shroud) was constructed because the older structure was not deemed strong enough to carry all the new digital transmission antennas.


Rowridge transmitters population coverage is around 1.75 million and its broadcasts can be picked up in many areas along the South Coast including Portsmouth, Southampton, Bournemouth, Fareham and Weymouth.


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We are more than willing to give advice to those actually purchasing from us. Could those only seeking information please just find the answer somewhere on this site, or ring an aerial installer local to them, or call the reception advice phone numbers.

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Rowridge transmitters.


Picture

David Foord

The Big Tower


If you`ve found this site informative and, hopefully, interesting as well,

please help us increase the number of people reading it.


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History and general info of Rowridge Transmitter


Rowridge transmitter coverage (area & population)


Digital power output, aerial group and polarisation of Rowridge transmitter


Possible extra (future) channels from Rowridge


Our TV aerial recommendations for Rowridge


Rowridge external links


Pictures of Rowridge transmitter


The wrong aerial for Rowridge


Rowridge`s graph (its transmissions v our aerial recommendations)


Rowridge`s channels/frequencies (including alternative transmitters)


How to combat continental co-channel interference


Details of French transmitters

Subjects are listed on this page in the following order :

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There is one interleaved spectrum channel allocated to Rowridge, CH29, this may be used for a local Southampton TV channel. In addition, there are two planned lower power HD MUXES to be transmitted (in the CH 31 to 37 gap) on CHs 31 and 37. All the aforementioned channels are due to be transmitted horizontally polarised and can be picked up by all A group aerials.

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For Rowridge we recommend the DM log for strong signal areas, the Log36 for medium signal areas, the Yagi18A for outside installs in poor signal areas, the XB10A for loft installations in poor signal areas, and the XB16A for those with the most marginal signals. Unless you have a massive loft we`d normally recommend the XB10A over the XB16A for a loft install due the smaller size of the former aerial, plus the fact it can be end mounted.

The dimensions and test performance of the aerials can be found on the relevant tables.

The channel planners were able to fit all the Digital MUXES within the A group so those in poor reception areas can take advantage of the superior performance of an A group aerial over a wideband. In fact such is the widebands inferiority at the bottom of the band that there is no such thing as a “High Gain” wideband aerial for the A group frequencies and nobody should ever fit a “high gain” wideband on an A group transmitter, e.g Rowridge. If the site is in a poor spot an A group aerial should be used. On the other hand if the signal is strong (or medium) then by definition it doesn`t need a “high gain” antenna anyway !  Under these circumstances a Log Periodic should be fitted instead.

See Rowridge Graph and the wrong aerial for Rowridge.

See this customer Aerial Report.

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Rowridge channel allocation guide


This also channel allocation guide for Rowridge also includes the same information for other potentially co-receivable TXs within the Rowridge coverage area, namely Midhurst, Heathfield, Crystal Palace, Whitehawk Hill (Brighton), Guildford, Hannington, Mendip, Oxford, Salisbury, Stockland Hill and Beacon Hill. The channel allocation guides can be very useful in the diagnosis of co-channel  interference problems and can also be invaluable if you are trying to find a spare channel for a modulated output (e.g. for a Sky box or CCTV system) to be added to your TV setup/distribution system without suffering from co-channel.


Also check Rowridge`s thirty four smaller relays and the French Transmitters.


The frequencies given are for (most) digital MUXES, for analogue channels deduct 3MHz.

It is not unknown for those on Rowridge to suffer co-channel interference from the continent particularly during periods of high pressure (this was the reason that the transmitter was made dual polarity at switchover). If you live to the north or NW of the transmitter your aerial is also pointing at France !

Rowridge is an A group transmitter.

Since DSO Rowridge transmits all its digital output in both horizontal and vertical polarity. Rowridge is the only main transmitter to do this (the other dual polarity transmitters are all relays) and it is to help alleviate co-channel interference with the continent. If you get interference with a horizontally polarised aerial you have the option to go vertical which should decrease the co-channel. In fact vertical polarity is now recommended (by some) for all installs. Whether HP or VP is preferable will depend very much on where you live. All 6 MUXES are transmitted at 200kW on vertical, but on horizontal only the first 3 (the PSBs) are at this power, MUXES 4 to 6 are "only" 50kW, though this is still pretty high power, remember that they were transmitted at 20kW pre DSO ! (This is to avoid co-channel on these 3 MUXES with Crystal Palace). On the other hand, the planned lower power HD MUXES are only being transmitted on horizontal polarity. Furthermore polar plots of aerials are tighter when they`re horizontally polarised.


Ofcom report that, unsurprisingly, Rowridge doesn`t transmit to the South !


Rowridge is a very powerful transmitter, in fact it is the joint most powerful in the country for its vertically polarised output (4th most powerful for its horizontal output). In addition it has thirty four* smaller repeaters to increase its signal coverage.


* Including Whitehawk Hill plus its relays, but only counting dual polarity repeaters as

one transmitter.

The dotted lines are the 2 planned lower power HD MUXES