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Wrotham (Kent, England) analogue radio transmitter

sa_gmapsGoogle mapsa_bingBing mapsa_gearthGoogle Earthsa_gps51.320,0.288 or 51°19'13"N 0°17'15"E


UK Free TV shows the coverage area for a radio transmitter as a coloured overlay (orange for FM, other colours for DAB) on the grey map. We have computed the coverage by combining the terrain with the official radiation pattern. A single click will select the transmitter to view the coverage for a single site, and a double click goes to a page showing full details. Click on the buttons in the right-hand corner of the map to choose from different frequencies (or multiplexes for DAB).

Are there any planned engineering works or unexpected transmitter faults on the Wrotham (Kent, England) mast?

No problems on any service. BBC


 

Local transmitter maps

Wrotham DAB Wrotham AM/FM

Comments
Wednesday, 11 January 2012
Dave Lindsay
sentiment_very_satisfiedPlatinum

2:25 AM

Why is BBC Radio 1 at half ERP to the other three national BBC stations?

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Dave Lindsay's 5,724 posts GB flag
Monday, 16 January 2012
Briantist
sentiment_very_satisfiedOwner

7:11 AM

Dave Lindsay: As it was the last BBC network to be provided from the transmitter, it is probably at reduced level to protect another transmitter.

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Briantist's 38,914 posts GB flag
Friday, 26 October 2012
R
Rishi
12:11 PM

I want to see where the AF switch happens for a particular station (say Radio for example) between 2 overlapping transmitters (between Manningtree transmitter and Wrotham transmitter for example, as I live in Essex) as I drive along, is there a way to test this switch repetitively?
Thanks.

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Rishi's 1 post GB flag
Friday, 10 January 2014
C
chris
7:17 PM
Broadstairs

I am right in thinking some years ago the ERP from this transmitter was double that of now?

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chris's 16 posts GB flag
chris's: mapC's Freeview map terrainC's terrain plot wavesC's frequency data C's Freeview Detailed Coverage
K
KMJ,Derby
sentiment_satisfiedGold

10:05 PM

chris: According to Information Sheet 0908(20)9402 for Wrotham the erp is 250kW for Radios 2/3/4 and 125kW for Radio1. This is the combined power for mixed polarisation, so a dipole would effectively only see half that amount in whatever plane it was positioned. I wonder if the powers given now take that fact into account.

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KMJ,Derby's 1,811 posts GB flag
Saturday, 11 January 2014
C
chris
1:43 PM
Broadstairs

KMJ
Could well explain it.
Chris

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chris's 16 posts GB flag
chris's: mapC's Freeview map terrainC's terrain plot wavesC's frequency data C's Freeview Detailed Coverage
K
KMJ,Derby
sentiment_satisfiedGold

6:28 PM

chris: The original VHF/FM transmitters were set up to transmit Radios 2/3/4 with horizontal polarisation. It was intended at that time for listeners to use fixed receivers connected to an outdoor aerial. From memory each service then had an erp of 120kW. In due course, in order to improve reception in cars, the Wrotham site was re-engineered with a new mast, antenna and transmitters.so that from December 1981 an additional vertical component of equal magnitude to the horizontal component was added to the signal. So now have 125kW horizontal plus 125kW vertical. This effectively doubled the transmitter power, hence the mention of "250kW Mixed polarisation" in transmitter listings. A listener using their existing horizontal aerial therefore received a signal of similar strength to the one they had before the alterations, whereas a listener with a vertical aerial would now also have a similar signal, when previously there would have been little or no reception - at least that is the theory, although in practice reflections from hills and buildings come into play.

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KMJ,Derby's 1,811 posts GB flag
K
KMJ,Derby
sentiment_satisfiedGold

6:34 PM

Briantist: Has Ofcom changed the way transmitter powers are quoted in documents?

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KMJ,Derby's 1,811 posts GB flag
A
Alex
11:05 PM

KMJ,Derby: Not as far as I know. What makes you ask?

NB with V and H transmissions of the same strength, a dipole receive antenna at 45 degrees across the direction of signal will actually get about 1.4X the signal it would get when perfectly vertical or horizontal.

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Alex's 4 posts GB flag
Sunday, 12 January 2014
R
Richard Davis
sentiment_satisfiedBronze

8:22 PM

What Alex says would be true if the horizontal and vertical components of the signal were transmitted exactly in phase with each other. In that situation, the net result is a signal which is "slant polarised", ie.its plane of polarisation is at 45 degrees, and so you'll get the strongest signal if your receiving dipole is also at 45 deg - as Alex implies, the signal received by either a vertical or horizontal dipole will be 3dB lower in strength. However, this assumes that the dipole is offset from the horizontal or vertical by 45 degrees in the same direction as the radiation produced by the transmitter (eg clockwise) - if you offset it by 45 deg in the other direction (eg anticlockwise) you'll get nothing! Thus you're still in the situation where the received signal strength varies with the orientation of the receiving aerial.
To get round this, most BBC transmitter sites (certainly all the main ones and also many of the low power repeaters) use an aerial configuration which produces circular polarisation. This is acheived by delaying the feed to one section of the aerial relaive to the other so that the horizontal and vertical components are 90 deg out of phase with each other, resulting in a signal whose plane of polarisation rotates, making one 360 deg rotation per cycle. This means that a dipole aerial with any orientation (horizontal, vertical or slant at any angle) will receive the same signal strength. That strength, however, will be 3dB less than would be received by a dipole receiving a plane polarised trnsmission of the same power so, as KMJ says, the present 250kW transmitters are giving approximately the same effective signal strength as the 120kW horizontally polarised ones they replaced.

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Richard Davis's 26 posts GB flag
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