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What is the Inversion Effect and why does it effect my Freeview TV reception?

What is the Inversion Effect and why does it effect my Freeview TV reception?

What is the Inversion Effect and why does it effect my Freeview
published on UK Free TV

Under normal circumstances, the signals from each television transmitter can only be received by those homes and businesses that have aerials that have a direct line-of-sight to the transmitter.

(The Inversion Effect is also known as "Tropospheric Ducting")

The part of the signal from the transmitter that is directed upwards simply escapes into space and are lost.

When there is high atmospheric pressure (Met Office - Surface pressure charts) as the sun heats up the ground the warm air gets trapped underneath the colder air higher up. At the point where the warm air gets trapped under the cold air this creates a layer that is, in effect, a mirror for the television signals.

This means that signals that would otherwise be impossible to receive can suddenly effect your television reception.

The digital television signal uses a format called COFDM (coded orthogonal frequency division multiplexing) and this incorporates the ability to ignore reflected digital signals.

However, analogue television signals did not co-operate with each other and the picture quality is reduced. The very weak digital signals that were used before digital switchover for Freeview were badly effected by interference from reflected signals from adjacent analogue transmissions.

I recommend you look at the Tropospheric Ducting Forecast for VHF and UHF Radio and TV page for a current forecast - yellow, orange, red, and pink indicate that conditions are perfect for the effects listed above.

Links to current pressure data

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Tuesday, 22 February 2011

5:43 PM

Margaret: As long as your have a rooftop aerial you should have excellent reception of multiplex 2 - can you please see Single frequency interference | - independent free digital TV advice for some help.

Yes, the signal will be even stronger after switchover.

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Briantist's 38,915 posts GB flag
Wednesday, 20 April 2011
Dennis Cartwright
8:37 PM

Why is BBC1 & BBC 2 picture all broken up where ITV Ch4 & 5 etc are fine.

BBC is unviewable

This has only happened overt the last two or three days.

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Dennis Cartwright's 1 post GB flag
Dennis's: mapD's Freeview map terrainD's terrain plot wavesD's frequency data D's Freeview Detailed Coverage
Thursday, 21 April 2011
Graham Lewendon

3:10 PM

All freeview tuners have lost Dave & sky news
Tuners range in age & type NB :-one was only instaled Monday 18-04-2011 is hd enabled which it tunes all 4 HD offerings fine have checked for engineering work on anglia TX seems switch over compleated ok so why no sky news or is problem inversion issue?

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Graham Lewendon's 29 posts GB flag
Wednesday, 18 May 2011
Bill Wallace

7:25 PM

I don't have any reception problems, only channel numbering on a newly acquired Technika TDVB77 set top box. The channels are numbered in what I suspect is the order they were decoded from each mux and, whilst they can be resorted, there appears to be no provision for renumbering in LCN order.

I can't find any tech support for Technika in the UK (Note, this is NOT a box from Tesco which is a major retailer of Technika products)so I wonder if anyone can help with the problem or advise me of a link for tech support?

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Bill Wallace's 43 posts GB flag
Bill's: mapB's Freeview map terrainB's terrain plot wavesB's frequency data B's Freeview Detailed Coverage
Thursday, 19 May 2011
Wednesday, 25 May 2011
Liam Guest
1:48 PM

WV10 9EF(aerial in Loft)
Hello my problem is when i watch a recording of Family Guy or American Dad every episode it goes out of sync and skips forward this only happens on those two shows any other programme on BBC THREE or all the other channels are fine thank you.

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Liam Guest's 1 post GB flag
Liam's: mapL's Freeview map terrainL's terrain plot wavesL's frequency data L's Freeview Detailed Coverage

3:36 PM

Have you tried watching them LIVE?

Need to know if it is what is recorded that is bad, or the playback.

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Steve's 1,173 posts GB flag
Steve's: mapS's Freeview map terrainS's terrain plot wavesS's frequency data S's Freeview Detailed Coverage
Thursday, 26 May 2011

8:05 AM

Liam Guest: Loft aerials are recommended for reliable Freeview reception, but I would see Freeview intermittent interference | - independent free digital TV advice for suggestions for this rather odd problem.

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Briantist's 38,915 posts GB flag
Sunday, 5 June 2011
Rick Whitehead
12:50 AM
Milton Keynes

I'm on the west of Milton Keynes and pre switchover I installed a log40 aerial with line of sight to Sandy Heath thanks to a beefy 12ft mast on gable end wall.
I'm using best quality copper shielded satelite cable and f-connectors and no wall plates (terminating at digi TV or STB). Before switchover we had perfect signal strength and quality with no issues. Post switchover we continued with no problems. But in the last 2 weeks signal strength now shows as fluctuating depending on mux but overall approx 15% lower and we now experience data errors resulting in pixelation and sound squeeks as well as sound picture sync delays.
I've retuned & factory reset on 2 different tuners umpteen times which sometimes for a short period fixes sync delay but essentially it feels like the power got turned down at sandy heath??
I had some great professional advice when choosing my non-wideband directional aerial (log40) and no issues until recently. I still have line of sight and I've tried altering aerial direction by a few degrees either way just to be sure (not fun 10-11m off the ground!)
Any advice gratefully received - thinking of not paying my TV license next.

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Rick Whitehead's 2 posts GB flag
Rick's: mapR's Freeview map terrainR's terrain plot wavesR's frequency data R's Freeview Detailed Coverage
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