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.
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
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 !
Above we have two graphics illustrating co-
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).
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-
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.
If you receive your signal from Rowridge and suffer from co-
Below is a Channel Allocation Guide for the French Transmitters most likely to give
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).
When UHF TV started in this country the transmission planners did their best to minimise
Differing transmission polarities are also used to try and minimise problems from
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-
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)
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.
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.
If you`ve found this site informative and, hopefully, interesting as well,
Subjects are listed on this page in the following order :
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-
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-
On the other hand aerials polar plots are tighter when horizontally polarised.
Rowridge is an A group transmitter.
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.
There is one interleaved spectrum channel allocated to Rowridge, CH29, this may be used for a local Southampton TV channel. It is within the A group but it`ll only be transmitted in vertical polarity (if it`s ever transmitted....). In addition, there may be two more HD MUXES transmitted (in the CH 31 to 37 gap) on CHs 31 and 37. All the aforementioned channels can be picked up by A group aerials.
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 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.
This also channel allocation guide for Rowridge also includes the same information
for other potentially co-
Note the gaps in the table below for channels 31 to 35, 37 and 61 to 68, they`re reserved for “other uses”.......
The frequencies given are for (most) digital MUXES, for analogue channels deduct 3MHz.
It is not unknown for those on Rowridge to suffer co-