Full Freeview on the Rowridge (Isle Of Wight, England) transmitter

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3:46 PM

Christopher Martin James: The existing should be fine (assuming it's not damaged of course).

Friday, 15 February 2013

Idris Martin
10:08 PM

Hi
I live in & have fitted a high vertically polorised ariel with head set up by compass bearing then fine tuned with the strength meter in the tv's menu.
However,the ststions on channel 22 keep breaking up, signal strength ok, but poor except on a sunny day when it is ok.
Can somebody explain why the other multiplex ore ok but not channel 22.

Idris Martin's 16 posts GB flag

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10:31 PM

Idris Martin: Because different frequencies are affected by objects in the path to differing degrees. Different frequencies radiate slightly differently from the .

You have a issue. The fact that it is OK on a sunny day suggests that there is vegetation somewhere in the path.

The terrain plot shows that the Purbeck Hills are in the way and so you have no where near line of sight. For that reason I think that a high- is likely not to be the best device.

The higher the gain, the narrower the acceptance "beam". As you aren't anywhere near line of sight, you don't have anything to aim at. Rather, your objective is to pick up what you can.

As requires good quality (digits intact) a wider acceptance angle could perhaps give better results. It stands to reason that if the quality of the signal across a wider angle is better than across a narrower one then reception is better, even though a lower gain aerial has been used. You can increase the signal strength with an , but you can't repair its quality.

If it is a high-gain aerial then it isn't "high" gain on the you are trying to receive as the gain of wideband yagi aerials drops off on lower channels.

As you have no where near line of sight then it might be worth trying turning the aerial a bit to see if it improves it.

Saturday, 16 February 2013

Roy Barton
3:08 PM
Wimborne

For years we had perfect at BH21 7BT. Over the last few months it has degraded. I recently rescanned all the and it was puzzling why BBC1HD should have moved from ch 50 to ch101. But tht is trivial compared to our real problem. As a qualified electronics engineer I can't understand why signal strength and for BBC on Channel 24 is 99% but signal strength of Film4 on channel 28 is almost non existent on a good day as measured by our sharp TV signal strnegth is high but n a bad day quality is down to 1% or at all. I have advice that we should rotate our so that is is Vertical polarisation. We have not tried it yet. WE are confused as the UKfree.tv website indicates that is H. But there are clues that it might be also V. Any info on this is very confusing, probably because some info on your website is out of date.
Please clarify. Should we continue pointing at rowridge and rotate our aerial through 90 degrees so the dipoles are vertical? I guess we should be using a type A aerial. Would you confirm that a aerial is not to be recommended for our location.

Roy Barton's 13 posts GB flag

Roy's: R's Freeview map R's terrain plot R's frequency data R's Freeview Detailed Coverage

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3:45 PM

Roy Barton: The short answer is yes, rotate your for vertical polarisation with ; there isn't, generally, a requirement to replace the aerial. The information at the top of this page is correct and says that each is broadcast horizontally and vertically.

The (sensitivity) of yagi aerials drops on lower . A yagi is a greater compromise than a Group one as by the time you get down to Group A channels the gain is low. Manufacturers will quote the gain on the highest channel which is likely to be not what you're using it for. Rowridge is all Group A, so for that reason if you use a yagi then use a Group A one. For example gain curves that illustrate the point, see:

Gain (curves), Again

Above it does say "To receive from the Rowridge you will require an aerial of group A positioned horizontally." I will alert the site administrator to see if it can be changed.

The longer explanation: There are the PSB (Public Service) channels and there are the COM (Commercial) channels. The COMs don't have as extensive a coverage as the PSBs. This is due mainly to the fact that small relays don't carry them, but there will also be a few who won't get them reliably even though they use a transmitter that broadcasts them.

Basically, the PSB- is designed to serve all areas that the former four-channel network did and without requirement for existing aerials to be adjusted or replaced. The COM transmitters fit in where they can and in some cases require a replacement aerial, or in the case of Rowridge, vertical polarisation may be beneficial.

Rowridge broadcasts horizontally so as to be backward-compatible with existing aerials.

Because the COM channels fit in where they can, the channels that are used for them are reused by other transmitters in closer proximity than those of the PSB channels. Rowridge's COMs are co-channel with those of 's in the and 's in the east. This is the reason that Rowridge's COMs are effectively restricted horizontally; it's so they don't spread as far. Turning your aerial for vertical polarisation will increase the "rejection" of the unwanted Stockland signals (which are only horizontal).

Vertical polarisation may also reduce co-channel during lift conditions. Like the UK, France uses horizontal polarisation for high-power transmitters. (Rowridge being the one exception.)

Roy Barton
11:24 PM
Wimborne

John Lindsay. Thank you for your answer. Can I assume that a wide band would be a definite bad choice?. (I bought one just today **** )
I also purchased a Labgear aerial . In the blurb it states it is for terrestial TV DTT and radio T- and no mention of DVB-T. Is it safe to assume that a MSA111 would not degrade the in any way. (Other than when it might be overloaded) ?

Roy Barton's 13 posts GB flag

Roy's: R's Freeview map R's terrain plot R's frequency data R's Freeview Detailed Coverage

Sunday, 17 February 2013

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3:08 AM

Roy Barton: A yagi is not a good idea for a Group A .

Log periodic aerials have very flat curves and therefore the same issue does not apply; they are fine. See:

Rowridge Transmitter

Using the is fine. It needs to be as close to the aerial as possible because it will be amplifying the noise picked up in the aerial lead, which is what you don't want (poorer snr). See:

Television Aerial Boosters / Amplifiers, Splitters, Diplexers & Triplexers

If you have a Group A aerial, then you should re-orientate it for vertical polarisation. A wideband aerial isn't necessary (over that of a Group A one) because all of 's are within Group A.

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3:44 AM

Roy Barton: Here is a plot of the terrain between you and the :

Terrain between ( m a.g.l.) and (antenna m a.g.l.) - Optimising UK DTT Freeview and Radio aerial location

You will note that one mile away, the ground obscures line-of-sight. This corresponds to Holt Heath.

Therefore, your task is to receive what is "coming over" the brow. (Imagine if it were a light.) As far as the COMs go, you may have to contend with from 's COMs, which are co-.

You are only 28 miles away; that said, we don't know how the COMs might have restriction WRT the PSBs, in your direction. The UK Coverage Checker suggests that they may be a bit inferior to the PSBs. The predicted figures are that one third of viewers won't get the COMs, so they must be inferior in some way.

Obviously, with Stockland being in the opposite direction, the reflector is important WRT blocking interference.

As I say, I would start by changing the existing to vertical polarisation and take it from there. Only then will you know whether it is sufficient to pull in the COMs or not.

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3:59 AM

Roy Barton: See:

http://www.wrightsaerials….pdf

Tuesday, 19 February 2013

Roy Barton
12:59 PM

Roy Barton:
John Lindsay. I really do appreciate the detail in your answers. I have checked with the manufacturers of my aerial (not yet fitted). It is a labgear LAB450/WS

Labgear

They say it is not a Yagi, but when pressed they said it was based upon a Yagi but having 3 booms they say it was strictly not a Yagi. They went on to say as regards a log periodic it would perform as well as a group A on 28 where we have the problem. Some local stockists only stock wideband, but one distributor offers just one item in Group A, and it less than 25% of the cheapest wideband. Labgear only manufacture wideband.
You have made it clear what I should do. I will try to get a refund on the wideband and fit the cheap group A on vertical polarisation. To me this seems to be an aerial jungle. I would appreciate your comment. LAB450/WS is it worth messing with? (BH217DX)