TV auto-tuning to wrong transmitter

[abenn]

A friend of mine is having trouble tuning his new Freeview TV, a Samsung Series 3 TC300. He (and I) can access all the menus, and set all the options okay (language, country, aerial or cable, etc.), and it goes through the auto-tuning process seemingly without a hitch.

The problem is that channel 1 then displays "BBC1 LON", instead of BBC Anglia (or East?), so he gets London news and weather after the main BBC news, instead of local news.

His aerial seems to be aligned okay towards Sandy Heath, our local transmitter, and looks similar to all the other Freeview aerials on neighbours' houses.

He lives in Letchworth, Herts. So, how and why should it be tuning to, seemingly, a more-distant transmitter in the opposite direction? And how can I resolve the issue? I see there's a menu option for manual tuning -- would this allow me to force it to the Sandy Heath transmitter and, if so, what info do I need to allow me to do that, please?

 

[rjm2k]

You can manually tune using the details for your transmitter from sites like this http://www.ukfree.tv/txdetail.php?a=SE222128

 

[abenn]

Thanks for that link rjm2k. I see from that site that Sandy Heath transmits the BBC channels on channel 27, whereas Crystal Palace does them on channel 23.

So, do I simply need to make a list of all the Sandy Heath channel numbers, and then use them in the manual tuning option?

I also see from the map that Crystal Palace is practically 180 degrees from Sandy Heath, at our house location. So seems like my friend is receiving his signal from the wrong direction -- presumably he could do with an aerial with a better reflector on it?

 

[rjm2k]

Yes that's how you do it. Not sure a different aerial would help tbh but I'm not an expert

 

[abenn]

Thanks. I'll go through the manual tuning with him next time I'm round his house. It'll be a new experience for me, auto tuning has always done the job so far.

 

[Sam Gangee]

Fit a 20dB variable attenuator in the aerial feed near the TV. Much easier!
http://www.satcure.co.uk/accs/page15a.htm#variable

Edit: you might also need an 18dB (fixed) UHF attenuator.

 

[Diyisfun]

If only I could get the London local news, since moving to Norfolk. There
is nothing to report on here, when it gets dark they tell you.

 

[plugwash]

If only I could get the London local news, since moving to Norfolk.

If you really want to get it then put up a dish.

 

[ericmark]

I have the same problem TV continually wanted to be retuned although option turned off. In the main use Sky so for a while just unplugged aerial but like watching UK History which is not on my sky bundle so put up an old loop aerial in the window. Works fine. Use the house to shield unwanted signal. Likely attenuators will work but much depends on the tuner only have a problem with Panasonic all other TV's work fine.

 

[abenn]

Fit a 20dB variable attenuator in the aerial feed near the TV. Much easier!
http://www.satcure.co.uk/accs/page15a.htm#variable

Edit: you might also need an 18dB (fixed) UHF attenuator.

So, you're suggesting the signal's too strong, and if I attenuate it the Alexandra Palace signal will be so weakened the TV will ignore it? But why would the TV select the signal from the furthest away transmitter, irrespective of how strong they are? It's not a fault in the TV, is it?

Oh, here in Letchworth we get changing weather to report in the local news, as well as day and night, Diyisfun

 

[Sam Gangee]

You didn't provide an accurate postcode so I can't check the signal levels. I'm guessing that Crystal Palace will be about 20dB lower than Sandy Heath, therefore an attenuator adjusted up to about 30dB should effectively remove the CP signal, allowing the TV to tune in SH only. The attenuator can then be removed or reduced till next time you need to retune.

 

[ericmark]

I worked in Sizewell in Suffolk and when going home could talk to my friends there all the way until I reached Letchworth on 2 meter ham radio it is so flat in fact I have talked through the Ipswich repeater from North Wales if local one is not open on good days. Isotropic propagation is a real problem for TV in that area of the UK.

Here in North Wales I can also get many TV channels but not as many as where you live and I would think a more directional aerial and attenuation would be required.

I gave up and I now use a free to air box and satellite but most is down to TV design and how it can be fixed not to auto retune.

 

[abenn]

My friend is at SG6 2HY. Looking at a map, could it be Hemel Hempstead transmitter he's receiving, for it also carries BBC London? It's closer than Crystal Palace, though it's off to one side compared with the 180-degree bearing difference between Sandy Heath and Crystal Palace. We seem to be just within the coverage area of both Hemel and Crystal Palace, though Sandy Heath is obviously much closer.

 

[Sam Gangee]

According to the postcode, Hemel would be almost impossible to receive. Sandy Heath is very strong and Crystal Palace is 25dB lower. So my guess of a 20 - 38dB attenuation still looks good.

http://www.wolfbane.com/cgi-bin/tvd.exe?DX=L&HT=10&OS=SG6+2HY

Another point to note is that CP and SH transmitters are diametrically opposed so the aerial is picking up CP from behind (or pointing the wrong way). Either way, it's not a very good aerial if it's picking up so much signal from the rear. A Log Periodic would be best.

 

[abenn]

Thanks Sam. I'm with you on the aerial, but my friend is a bit short of cash so doesn't want to spend money on getting a new one erected. The reflector on his present one looks like a flat plate with slots punched out of it, rather than the V-shaped multi-bar ones I see on some other houses. Sorry, I don't know the technical terms. An attenuator looks like the cheapest option.

One question for my own education, if I may. The table you've linked shows that CP is 25dB less than SH transmitter. But why is 25dB attenuation appropriate -- don't we want to eliminate the CP signal if possible, i.e. 43dB attenuation? Or is 25dB simply a good compromise, and going further would reduce the SH signal too much?