tv problems...in cornwall?

[Predictable Bob]

I'm with Matt on this one BUT I have a simple query .......

How do you know what your best option is ? Do we have to resort to empirical means ?

[Waits for a useful response but expecting an affirmative]

[MattF]

How do you know what your best option is ?

With regards to which part? Transmitter, aerial type or other?

[Apache]

high gain aerial can cause as many problems as it is supposed to cure if used within the wrong conditions. A good narrow beam aerial is preferable most times, whatever the aerial type, but a high gain aerial in a good reception area will do nothing more than swamp

High gain = directionality Matt. Always.

[Sancho]

Just to interject in this sea of nerdism for a minute: Rob, your new aerial installation isn't up to scratch. If it was done professionally, get them back to sort it out. If you did it yourself, get up there and do it properly...

[MattF]

High gain = directionality Matt. Always.

Granted, narrow beam improves reception and gain, but the narrow beam is primarily to reject side and rear beam interference/pickup. Gain, with regards to television antenna, doesn't necessarily go hand in hand with directionality like for like. They design high gain aerials that have a very broad beam range. Directional aerials aren't always designed for improved gain. Most of the time their primary goal is reduction of unwanted signals, hence gain isn't always a primary factor in the design.

I know that sounds quite contradictory, but it makes sense.

[MattF]

If it was done professionally, get them back to sort it out.

Have you noticed the large amount of cowboys who call themselves riggers these days? Professional is a very loose term in the trade these days.

[Apache]

Wasn't talking about the reasoning behind using antenna A against antenna B, just stating the fact that directionality = gain. Theoretical isotropic antenna has a gain of 1, all antenna gain is referenced to this and all gain is related to the acceptance angle of the antenna because an antenna is passive. Unless you live within sight of the Tx, a high gain antenna shouldn't give problems to your TV as the AGC should take care of too much signal. Stuff like ghosting etc isn't due to the gain, its do to other factors.

[Predictable Bob]

With regards to which part? Transmitter, aerial type or other?

Transmitter selection

[Apache]

Have you noticed the large amount of cowboys who call themselves riggers these days? Professional is a very loose term in the trade these days.

I'm gonna get a 'professional' to put my scanner antenna up for me. I'm gonna wire it first, and just have him strap it to the chimney. Not cos I cant, just cos the gable end of the house looks pretty high and the block paving feels pretty hard

[MattF]

Wasn't talking about the reasoning behind using antenna A against antenna B, just stating the fact that directionality = gain. Theoretical isotropic antenna has a gain of 1, all antenna gain is referenced to this and all gain is related to the acceptance angle of the antenna because an antenna is passive. Unless you live within sight of the Tx, a high gain antenna shouldn't give problems to your TV as the AGC should take care of too much signal. Stuff like ghosting etc isn't due to the gain, its do to other factors.

I f*ing hate comms techs when they get technical.

All I can say is that your specific field varies somewhat to the domestic market. For one, if you think a domestic AGC circuit will deal with a large input, try it on something at home. It'll crap out quicker than you can blink. The input would have to be manually attenuated.

Secondly, (and I do know that this area ain't exactly my forte), this 'directionality = gain' is an extremely overly simplified statement. Extremely. Go out and buy a high gain T.V aerial and see how 'directional' it is. Unless you specifically ask for the exact antenna you require for a specific job, you'll get whatever they class best meets your 'request'. It ain't liable to be either what you want or need. Intended in a nice way, again, you cannot expect the rigid environment you work within with regards to specs to be anything like within the domestic orientated market. It is the same as you using a 2W resistor when a 0.5W resistor would suffice. Your equipment and designs have to be exact and highly reliable. The domestic market is a different beast.

Stuff like ghosting etc isn't due to the gain, its do to other factors.

I never suggested otherwise.

[MattF]

Transmitter selection

Look at which direction all of your neighbours aerials are pointing.

[MattF]

Not cos I cant, just cos the gable end of the house looks pretty high and the block paving feels pretty hard

Wouldn't worry about the block paving. You have plenty of 'protection'?

[Apache]

I f*ing hate comms techs when they get technical.

All I can say is that your specific field varies somewhat to the domestic market. For one, if you think a domestic AGC circuit will deal with a large input, try it on something at home. It'll crap out quicker than you can blink. The input would have to be manually attenuated.

Buying an aeriel for your TV without even a little knowledge is a bit like going to a tyre fitter and asking for 'a tyre'. It's easy to learn the very basics so at least you go into the shop a bit switched on and knowing what you are asking for. However, most local antenna installers will know what band you need, and where to point it.

A 'high gain' antenna, if it really is high gain, WILL be directional, in that it will have a smaller solid angle of acceptance between its 3dB points than an antenna with a lower gain. Thats physics. Aint no getting around it.

Incidentally, I can see our local mast from here. It's about a mile away, and our neighbour has the most enormous about 30 bay high gain antenna pointed at it for freeview. Picture's fine. The amount of signal he has will be somewhat more than average, but I bet its still only in the order of single figures dBuV, and if a modern telly's AGC cant cope with that, I'd be amazed.

Dont have any sensitivity figures to hand, or the will to drag myself to the bookcase for my antenna bible to work out the likely field strength on our roof from the Malvern Tx, but it sounds like a fun exercise for another day

I did do it a bit ago for the local 3G masts just to prove a point to someone (using a mobile next to your head you absorb much more RF than living 100 metres from a mast) who is scared of mobile phone masts.

I digress - yes yes, I'm a nerd.

[MattF]

Buying an aeriel for your TV without even a little knowledge is a bit like going to a tyre fitter and asking for 'a tyre'. It's easy to learn the very basics so at least you go into the shop a bit switched on and knowing what you are asking for.

Ah, but you're forgetting the whole point of this thread there. Seriously though, even a lot of riggers these days don't know much more than the basics. They're merely ladder monkeys, for wont of a better term. Good, truly knowledgeable riggers are a damned sight harder to find, so expecting someone not in the trade to do their homework may be somewhat of a large ask.

A 'high gain' antenna, if it really is high gain, WILL be directional, in that it will have a smaller solid angle of acceptance between its 3dB points than an antenna with a lower gain. Thats physics. Aint no getting around it.

Incidentally, I can see our local mast from here. It's about a mile away, and our neighbour has the most enormous about 30 bay high gain antenna pointed at it for freeview. Picture's fine. The amount of signal he has will be somewhat more than average, but I bet its still only in the order of single figures dBuV, and if a modern telly's AGC cant cope with that, I'd be amazed.

I'm not trying to argue with the maths or anything. I know better than to attempt that.

With regards to his setup, I honestly couldn't say. I've never rigged anything that close to a transmitter personally, so I have no idea what set of peculiarities that entails. I seem to remember some riggers mentioning that being so close to the transmitter can cause it's own set of reception problems, however. I just can't remember what the chuff they were.

Dont have any sensitivity figures to hand, or the will to drag myself to the bookcase for my antenna bible to work out the likely field strength on our roof from the Malvern Tx, but it sounds like a fun exercise for another day

I did do it a bit ago for the local 3G masts just to prove a point to someone (using a mobile next to your head you absorb much more RF than living 100 metres from a mast) who is scared of mobile phone masts.

I digress - yes yes, I'm a nerd.

Nerd doesn't even come close.

[mark g8awo]

Just to give you some thought a lot of the digital transmitters are running an average of 200w untill the switch over then they will be increasing the power to 2kw. These figures are not for all transmitters....just as a guide. I would not recomend just going to the local diy for some cheap poorly made aerial kits these are false economy and do not withstand the elements to well.
A proper rigger will have a meter for getting the best signal strength for the situation. Digital does not suffer the same traites as analogue with whats known as multipathing ( ghosting ). You can be in between 2 transmitters so you should not suffer crossmod. This is one of the reasons you see aerials with large reflectors to screen large signals to the rear. And please guys get rid of those faffin awfull y splitters i am forever seeing hanging out the back tvs they are the cause of most tv problems on the market. Get a distribution amp if you need to split the signal. Just think of it if you put a y piece in a hose line you get half the preasure at the two ends so you need a pump to compensate for the losses. the same theory is in respect to tv signals. ANd sparkys are the worse they think rf works the same way as electric when they twist wires together.
The use of good quality coax goes without saying I allways use double screen coax CT100. The coax you buy in the diy shops is ok for short runs but the average drop from the roof can drop the signal a good deal that can mean the difference of drop out and a solid lock .
If you get a rigger in do some homework make sure the company is registered with CAI this is the industry governing body and dont just take his word that he is registered with them. He should have good knowledge of your area and the transmitters available.

I am speaking from years of knowledge in the field covering the home counties and north London but i now just do large comms aerials some of them up 40m masts, more for pleasure than owt else