Hillsborough
Sheffield
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Rowridge TV transmitter (picture MB21)
Fawley (ex) Channel 5 Transmitter, the transmitting arrays are located on the chimney !
This transmitter was switched off on the 25th of March 2009 as part of
preliminary work for the Digital Switchover. (Picture MB21)
It is a fairly frequent problem for those on Rowridge to suffer from co-
interference from the continent, particularly during periods of high pressure.
This is due to picking up continental transmissions if you are situated to the
North or North West of the transmitter with aerials pointing towards the France etc.
External Links
The channel planners were able to fit the Digital MUXES (transmitted at 20kW) within the
A group along with the analogue stations, so an aerial change may not be necessary. Furthermore those in poor reception areas, who may require an
upgrade, 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.
For Rowridge we recommend the DM log for strong signal areas, the Log 40 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
The dimensions and test performance of the aerials can be found on the relevant tables.
Also see Rowridege > Attenuator !
Rowridge transmitter`s channels (post Mar 2009) in relation to the TV band and the gain of the aerials we recommend for it. DM Log Log40 Yagi18A XB10A XB16A
Also see other relevant A group curves and Rowridge > attenuator !
DSO is due to occur in February 2012. Unsurprisingly it has been confirmed by
Ofcom that Rowridge will stay as an A group at DSO.
After DSO Rowridge will transmit its entire digital output in both vertical and horizontal
polarity. Rowridge will be the only main transmitters to do this and it is to help alleviate
co-
horizontally polarised aerial this will give you the option to go vertical which should
decrease the co-
switchover installs, but only for aerials actually fitted after DSO ! Whether HP or VP
is preferable will depend very much on where you live. All 6 MUXES will be transmitted
at 200kW on vertical, but on horizontal only the first 3 (the PSBs) will be at this power.
MUXES 4 to 6 will only be at 50kW, though this is still pretty high power, remember
that they`re only transmitted at 20kW now ! Lower power on these 3 MUXES is to help
prevent co-
There are two interleaved spectrum channels allocated to Rowridge, CH29 and CH30,
which are both within the previously announced post DSO group.
All information sourced from Ofcom.
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.
If it`s a strong or medium reception area he should have fitted a Log Periodic aerial,
but if it`s a weak reception area an A group aerial should have been used instead.
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 6.7 dB more. We had a customer who was shielded from Crystal Palace transmitter by the Arsenal football stadium. He originally had a DAT75 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
Don`t get me wrong, I`m not saying these Tri Booms aren`t working for the particular
installations, but the fact is that on Rowridge the performance difference between one of these huge aerials and a decent Contract 10A would be minimal. The Contract would be about a tenth of the price and have much less wind loading as well ! We don`t actually recommend Contract aerials but our Log40 would perform just as well (over the A group frequencies) as any wideband Tri Boom antenna, yet have much less wind loading, still be
a wideband and have all the advantages that a Log Periodic aerial offers. QED #2
In my opinion if any installer tries to sell you this type of antenna 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) for 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 !
Also check Rowridge`s thirty five smaller relays and the French Transmitters.
The frequencies given are for the analogue channels, for (most) digital MUXES add 3MHz.
Note the gaps in the table below for channels 31 to 35, 37, 39 to 40 and 63 to 68, they`re reserved for “other uses”....
Note, as work takes place on various digital transmitters (to prepare for the DSO) you may
experience problems, e.g. with certain MUXES disappearing. First try rescanning your
TV / set top box (do it manually if possible), but if this fails to work check on Transmitter work
or call the reception advice phone numbers. Also see basic digital fault finding.
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.
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.
Power output is 500kW (erp) analogue and 20kW on all Digital / Freeview output.
The structure is 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 plans were submitted in May 2009 by the site`s owner Arqiva (spelt wrong, and I don`t like them anyway) to replace the existing structure with one 187m tall, to the top of the shroud.
See How High is High ?
Rowridge is horizontally polarised and is an A group for the 4 analogue channels plus all
the digital but post DSO Rowridge will be transmitted vertically and horizontally.
Note that MUX 2 was originally on CH 52 but was restored to the A group in 2007.
Analogue C5 from Fawley was turned off on the 25th of March 2009 as part of the
preliminary work required for Digital Switchover (DSO). C5 is still be available on digital
MUX3 from Rowridge. As part of this switchover process the channel MUX allocations
changed (though not to their “final” post DSO frequencies) and Freeview STBs needed
retuning. All MUXES are still within the A group and therefore (hopefully) receivable without
an aerial upgrade, though there is a chance that pre 1995 A group aerials may be weak on
reception of MUX5.
Due to the Black Art nature of RF (theoretically the MUX reallocation shouldn`t have made
much difference) some people did experience reception problems after the March mini-
Rowridge has thirty five smaller repeaters to increase its signal coverage.
For Rowridge transmitter`s TV frequencies/channels see its Channel Allocation Guides
from 25 Mar 2009 up to DSO and for after the switchover. These also include the same
information for other potentially co-
Hannington, Mendip, Oxford, Salisbury, Stockland Hill and Beacon Hill. This information
can be very useful for identifying possible causes of co-
transmitters which may give a superior signal. They 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-
Ofcom report that Rowridge does not transmit anything to the South, as one would expect !
Above we have two graphics illustrating co-
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 ! 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 unwanted transmitter is to the side of the alignment onto the required TX, the first option is
to try and mount your aerial so it`s shielded from the unwanted transmissions, e.g. down the
side of your house or on the other side of the chimney.
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 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.
If the unwanted transmitter is directly behind 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.
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-
"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.
from France
Above are the French Transmitters that tend to give the most co-
Further details of their frequencies for analogue transmissions and digital transmissions can be found by clicking on the relevant links. Radiation patterns can be found on this site.
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-
Below is a Channel Allocation Guide for the French Transmitters most likely to give
co-
Neufchatel, Abbeville, Lille, Boulogne and Dunkerque. The information was correct as of August 2009 but the transmissions will change as the French switchover occurs between now and the end of 2011. The links to the French sites (above) should be accurate. The proposed frequencies after French DSO are in the bottom table (thanks to Martin Watkins for the research).
If you`ve found this site informative and, hopefully, interesting as well,
How To Combat Co-
Co-
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-
co-
Bear in mind that the nearest country (East) past Belmont is about 200 miles past it ! !
Some think that after DSO (Digital Switchover), when the transmitters power will
be increased significantly, there may be more problems with co-
When UHF TV started in this country the transmission planners did their best to minimise
co-
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-
Differing transmission polarities are also used to try and minimise problems from
co-
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-
Let me be quite honest here, co-
There are three main weapons in the fight against co-
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.....
