Telly?

[ilona73]

oh wow!! i noticed you live in cornwall.... i used to live down there for a few years and used to love Pirate FM... Is it still going?? This was about ten year ago now i guess?

http://www.piratefm.co.uk/resources/stream.php

- local radio at its finest - well apart from the music - and the DJs

hahah i bet its really cheesy now i thought it was great.. thank god i grew up !!!

 

[Flyfisher]

Thanks for that Tacolneston info MdB. The sites I found were mainly full of photos of the transmitter mast, which shows there are all manner of anoraks amongst us. :wink:

I understand that motion jitter/distortion is an issue with HD camcorders as well; I think it's related to the type of sensor and the way in which the image is sampled. I'm a bit out of date with this stuff but I believe the earlier (CCD) sensors captured a full frame snapshot of a scene whereas the newer sensors (CMOS) continually sample the scene. With the frame capture method a moving object will 'stutter' across the screen but remain 'whole' whereas a continually sampled object will be distorted because it will move during the sampling period. Difficult to explain more clearly without diagrams. Film-based cinema, of course, is similar to the full-frame snapshot method, but each of the 24 pictures per second is projected twice so that the eyes 'see' 48 pictures per second, which is about the lower limit that avoids a flickering sensation. So cinema and video actually differ quite a bit in the way that images are presented to the screen, and thus our eyes, and various artifacts crop up as a result - and all that's without even considering the effects of interlacing. All this subtle stuff (among other things) is what defines the different viewing experience of 'cinema' and 'video', with many videographers striving to achieve a 'cinematic' look and feel to their work.

Apologies, I'm waffling on again.

 

[Flyfisher]

The perfect length for a DAB monopole aerial (a telescopic aerial) is 370mm (for pickup at 200MHz). Attaching a long wire to it isn't going to help.

That's a quarter-wave aerial, I think. I know it's a common length for many radio applications but is it really the 'perfect' length. Wouldn't a full-wave aerial give better reception, albeit rather more cumbersome? Or maybe the impedance matching would be all wrong? My radio theory is a bit rusty as you can tell!

 

[MdB]

The perfect length for a DAB monopole aerial (a telescopic aerial) is 370mm (for pickup at 200MHz). Attaching a long wire to it isn't going to help.

That's a quarter-wave aerial, I think. I know it's a common length for many radio applications but is it really the 'perfect' length. Wouldn't a full-wave aerial give better reception, albeit rather more cumbersome? Or maybe the impedance matching would be all wrong? My radio theory is a bit rusty as you can tell!

For a monopole yes (I believe). If it was twice the length (half wavelength) or four times the length (full wavelength) it will perform badly as the signal will just resonate in the monopole with little energy transferred for the receiver to pick up. I believe three quarter wavelength is sometimes used though.

The above assumes a good ground plane at the base of the monopole (unlikely) and various other things such as wire impedances which I can pretend to understand....

 

[MdB]

OK, so I've just put my money where my mouth is...

My wife has a portable DAB radio and was complaining that the signal strength was poor upstairs in the bedroom. I have just been up and measured the aerial and it is 620mm in length when fully extended which according to me is too long. The signal strength display was showing 56. Dropping the aerial length to 370mm increased the signal strength to 93 which was a more dramatic increase than I was expecting though I've no idea what the units of the display are.

Those with poor DAB reception might want to try shortening their aerial, it may make all the difference.

Makes you wonder why they make the set with a too long aerial though.

 

[Penners]

motion jitter and refresh rates

When I was doing my overly-exhaustive research into digital TV's, these subjects were thrown at me in various forms by successive salesfolk, to the point where I really got pretty confused about the whole issue.

However, the guy who eventually gave me clear advice (and from whom I bought), basically told me not to worry my pretty little head about them (in rather more diplomatic terms than that). He just advised a minimum of 100 Hz and an interlaced picture, and that's the spec I stuck to. I can honestly say that I don't notice any more motion blur than on our previous CRT set.

But here's another aspect of this topic. Yesterday I went to see the film "Avatar" at a modern multiplex cinema in Norwich. Fortunately I didn't expect the storyline to be intellectually challenging (so I wasn't disappointed), but I was interested in seeing the 3D technology. As the film began, an on-screen logo announced that it was showing in the latest digital technology, so I assume it was coming from some form of high-power digital projector.

In some of the very fast CGI action sequences of the film, I found the motion blur and jitter to be quite marked. Whether the 3D system enhanced this, or whether it was down to an unsatisfactory refresh rate on the projector, I don't know.

 

[Penners]

My wife has a portable DAB radio and was complaining that the signal strength was poor upstairs in the bedroom. I have just been up and measured the aerial and it is 620mm in length when fully extended which according to me is too long. The signal strength display was showing 56. Dropping the aerial length to 370mm increased the signal strength to 93 which was a more dramatic increase than I was expecting though I've no idea what the units of the display are.

Those with poor DAB reception might want to try shortening their aerial, it may make all the difference.

Makes you wonder why they make the set with a too long aerial though.

Hmmm - I found the opposite.

Having read your post, I went upstairs to where my wife keeps a portable Roberts DAB radio in the bathroom. Its telescopic aerial is considerably longer than 370mm and she always has it fully extended. The reception strength is shown by a line of blocks - the maximum is 17. At the aerial's full length it showed 12 blocks, but when I shortened it to 370mm this reduced to 8 blocks. When I extended the aerial to its full length and put my hand on it, the strength shot up to maximum!

 

[MdB]

Was the aerial vertical or off at an angle? It is the vertical distance that needs to be 370mm.

Any physical contact with the aerial on my wife's set caused the strength to go way down - the exact opposite of yours. Interesting things radio waves...

 

[Penners]

Yes, it was absolutely vertical.

If you'd asked me that question after the sun was over yard-arm, I might have been less confident...

 

[Flyfisher]

Interesting DAB aerial comments. I've also been playing but the DAB radio I'm using doesn't seem to have a signal strength indicator (the other one does but I don't have access at present). At full length, reception is on the verge of 'bubbling' but reduced to 370mm there is no 'bubbling' at all. But touching the aerial, or even moving close, increases the amount of 'bubbling', i.e. reduces the signal strength.

I also found some info on how to make a dipole aerial, which is two quarter-wave aerials with a 75 ohm feed impedance and can be very easily made with a length of 75 ohm coaxial cable (as for TVs). Just strip back 370mm of the outer sheath of the cable and twist the braid into a single 'wire'. Bend both the braid and the inner conductor at 90 degrees to the main cable so they form a length of 740mm with the coax in the centre and that's it. Hang vertically for the best effect. I hasten to add that I've not yet tried this myself but will try to find some old TV coax and have a go over the weekend. It sounds half-sensible anyway. The only problem is that my DAB radios don't have a separate aerial socket so I'll have to improvise somehow.

Going back to Penners' TV, it sounds like you found the ideal sales person! We certainly found 100Hz was a noticeable improvement when we bought our current CRT, but the whole interlace/progressive thing seems rather more content-sensitive.

I've read that digital projectors were originally introduced into cinemas primarily to enable simultaneous country-wide (or world-wide) release of films via satellite downloads to each cinema and to avoid the considerable costs incurred in making , distributing, collecting, cleaning, redistributing etc, physical duplicate films. These days, a lot of 'blockbuster' cinema is shot directly in video and combined with a lot of computer-generated images, so all these differnt artifacts creep onto the big screen as well. I think we're off to see Avatar 3D tonight; not so much for the story (for the reasons you mentioned) but more to see the latest in film-making technology. Odd really - I guess it was similar in the 'good old days' when 'the movies' were a novelty in their own right, never mind the storyline. Funny old world.

 

[Moo]

Ahem.

That's two of you who've come to goggle at Avatar and not popped in for light refreshment.

 

[Penners]

never mind the storyline.

I think you'll enjoy the experience. I found the 3D effect a bit unsettling at first, but once you get used to it, it certainly adds a remarkable extra dimension (pointless comment no. 154 :roll: ) to the film.

I reckon about 80% of the visuals are CGI, and the CGI characters and sets are remarkable. Up to now, CGI scenery and machines have been very effective, but people and animals have mostly been unconvincing (to me, anyway). I reckon Avatar has got the closest yet to achieving 100% convincing living creatures.

The storyline is a parable about the rainforests and their indigenous peoples. It's pretty predictable and facile (aka "Hollywood"), but is just about sufficiently absorbing to carry you through the almost 3 hours.

But visually, it's quite something. I hope you enjoy it.

 

[Penners]

That's two of you who've come to goggle at Avatar and not popped in for light refreshment

My problems with that delightful idea are several.

Firstly, being a country lad, I try to avoid the city-centre cinemas (except the lovely Cinema City). So I took the easy route to the Riverside complex, on our side of Naarch.

Secondly, the film goes on for about three days, leaving no time for any associated activities.

Thirdly, once ensconced in your lovely kitchen with a "light refreshment" in my hand, I know every well that I'd lose all motivation to be anywhere else.

 

[Flyfisher]

Sorry Moo, but we tend to go to Bury St Edmunds for our cinematic delights these days.
Lovely idea though.

 

[MdB]

I think you'll enjoy the experience. I found the 3D effect a bit unsettling at first, but once you get used to it, it certainly adds a remarkable extra dimension (pointless comment no. 154 :roll: ) to the film.

I reckon about 80% of the visuals are CGI, and the CGI characters and sets are remarkable. Up to now, CGI scenery and machines have been very effective, but people and animals have mostly been unconvincing (to me, anyway). I reckon Avatar has got the closest yet to achieving 100% convincing living creatures.

The storyline is a parable about the rainforests and their indigenous peoples. It's pretty predictable and facile (aka "Hollywood"), but is just about sufficiently absorbing to carry you through the almost 3 hours.

But visually, it's quite something. I hope you enjoy it.

That was my take on it too. Visually stunning, story line ok but well worth seeing in 3D.

 

[MdB]

I also found some info on how to make a dipole aerial, which is two quarter-wave aerials with a 75 ohm feed impedance and can be very easily made with a length of 75 ohm coaxial cable (as for TVs). Just strip back 370mm of the outer sheath of the cable and twist the braid into a single 'wire'. Bend both the braid and the inner conductor at 90 degrees to the main cable so they form a length of 740mm with the coax in the centre and that's it. Hang vertically for the best effect. I hasten to add that I've not yet tried this myself but will try to find some old TV coax and have a go over the weekend. It sounds half-sensible anyway. The only problem is that my DAB radios don't have a separate aerial socket so I'll have to improvise somehow.

If you could find a connection to the negative input to the first stage amp which is connected to the monopole you could then fix another 370mm wire to that going downwards to make a dipole. You don't need the coax, that is just useful for connecting the aerial to the receiver by some distance. It doesn't improve the aerial in anyway. The problem is finding the negative input if there isn't a connector. Improvisations won't work I am afraid. If you don't have an aerial socket then unless you have circuit diagram and are good with a soldering iron then you are stuck with a monopole.

For those with an aerial socket, the simplest dipole is made with two pieces of wire. Twist them together apart from the end 370mm. Position with one wire up and one wire down with the twisted part coming out horizontal. This type of simple dipole often comes with stereo systems to stick onto the wall.

 

[Penners]

If you could find a connection to the negative input to the first stage amp which is connected to the monopole you could then fix another 370mm wire to that going downwards to make a dipole.

Alternatively, you could subderivate a left-handed snib valve on to the chromendulator and parboil a doobrie-ferkin.

 

[wobs]

If you could find a connection to the negative input to the first stage amp which is connected to the monopole you could then fix another 370mm wire to that going downwards to make a dipole.

Alternatively, you could subderivate a left-handed snib valve on to the chromendulator and parboil a doobrie-ferkin.

Thall I induth a thunder thtorm Dr Frankenthtein?

 

[MdB]

If you could find a connection to the negative input to the first stage amp which is connected to the monopole you could then fix another 370mm wire to that going downwards to make a dipole.

Alternatively, you could subderivate a left-handed snib valve on to the chromendulator and parboil a doobrie-ferkin.

Thall I induth a thunder thtorm Dr Frankenthtein?

You are putting the lisp on for effect again aren't you Igor?

And stand up straight please.

 

[wobs]

Authentithity ith everything thir