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Aerial groups - new feature

There has been a lot of debate about aerial "groups" over the last few years...

There has been a lot of debate about aerial  groups  over the l
published on UK Free TV

In the olden days of black and white, 405-line television, when the frequencies used were "very high" (VHF), the UK two-channel television service was provided using a just 100 transmitters and reception needed a standard aerial.

Later the system was upgraded to "ultra high frequencies" (UHF) for colour and now uses over 1,120 transmitters with more channels on more frequencies.

To enable the best quality reception possible, UHF television aerials are produced in a number of "groups". Each group is designed to operate on a range of channels, blocking all others. This is to prevent interference from "other" transmitters and to decrease losses on those required.

Each group is designated a colour, which is used to mark the aerial. Whilst wideband (black) aerials are designed to receive on all frequencies, their performance can be below a grouped aerial.

The transmitter pages now show a table like this:

The three sections show the three phases. The first is that before digital TV was introduced. This example shows that a group A (red) aerial would have received the original four channels but a group K was required to also receive FIVE. The channel number for FIVE on analogue is shown with an asterisk because it is "out of designated group", group A.

The second section shows the "digital with analogue" phase, where the transmitter has the analogue services from above with the new low power digital services. It can be clearly seen that on this transmitter a group A aerial will not receive any digital services at all, and that even a group K aerial will not receive the multiplex B service on C67. The only choice for digital reception here is a wideband (black) aerial because it is the only coloured band that crosses from left to right.

(You can also see that some of the digital services have plus and minus symbols. This indicates these transmissions use a 166.67kHz offset.)

The final section shows the designated frequencies that will be used for digital television after switchover. Whilst the public service multiplexes BBCA, BBCB, D3+4 are back "in group" (group A), to receive all the multiplexes, including the two potential new ones, the only choice here is wideband.

The performance of grouped aerials for each transmission channel was defined by the old Independent Television Commission (ITC) and is:

The larger the value, the lower the signal level possible.

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In this section
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Saturday, 15 April 2023
8:40 AM

Q1:So whats the H for?

Digital Transmitter
Reception: 4444
Region: Wales
Grid SN 17204 30670
Distance: 47
Bearing: 328

Aerial Group Now: B H,B H

Q2:any tips on replacement aerial I should buy?
previous pic: Dropbox - previous-aerial-pointing-at-Preseli.jpg - Simplify your life

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Stephen's 1 post GB flag

9:28 AM

Stephen: H Indicates that the transmitter broadcasts in horizontal polarity (i.e. the aerial elements go side to side as in your photo).

We need a full postcode to be able to access the predicted signal strength at your location, but in general log periodic or Group K aerials offer the best option if you're in an area with reasonable signal strength and are suitable for receiving the entire UHF frequency range used for Freeview.

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StevensOnln1's 3,639 posts GB flag

2:16 PM


Considering your location, estimated to be on the coast of the Gower where you'll periodically be exposed to very strong winds, as suggested an aerial such as a Group K Log Periodic which has low wind resistance would likely be best.
Assuming that you haven't had frequent issues in the past with picture break-up/pixellation and considering the distance I'd be picking the 28 element one such as -
28 Element Log Periodic Group K Aerial - Blake UK
If you have had more regular picture pixellation then go for the 56 element one
56 Element Log Periodic Group K Aerial - Blake UK

You'll need an F-connector for the aerial, and replace your coax with decent quality double screened cable such as CT100.
If you don't get it direct from Blake, the 28 element may be available from Tool station (31278) which although said to be the Group T stock in many stores seems to be Group K (T will work though).

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Chris.SE's 4,191 posts GB flag
Sunday, 16 April 2023

2:46 AM

StevensOnln1: Just a side note; normally, polarity relates to +/- or in the case of magnetism, north/south; in this case, we talk about polarisation, do we not?

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diogenes's 25 posts US flag
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