There's an easier way than that: if the TV is using RGB then its colour (saturation) control will have no effect. If the picture goes to black and white when you turn the colour right down, the interface must be either composite or Y/C, not RGB.
That's true of impulsive interference or other short-term effects, but tropospheric co-channel interference (which was the context) will tend to last for minutes or hours and if its strong enough to push you over the 'digital cliff' then you will get a blank screen (or frozen frame, or BSofD, depending on the decoder).
A half-wave dipole has a 'natural impedance' of 75 ohms and that's what gave rise to 75 ohm coax originally. 75 ohms is also the impedance at which an air-spaced cable of a given o/d has minimum loss (c.f. 50 ohms for a solid polyethylene dielectric cable).
A TV Yagi doesn't have a natural impedance of anything in particular since adding reflector and directors tends to lower the feedpoint impedance; in particular the spacing between the driven element and the first director can have a dramatic effect. The design of TV antennas is still a largely empirical black art (despite some impact from CEM techniques) and involves a juggling act between impedance, gain and bandwidth. Just optimising for maximum gain would give narrow bandwidth and an impractically low feedpoint impedance.
Almost -- I'm saying that there should be a balun at the aerial feedpoint because the aerial is balanced and the coax isn't. The balun's impedance ratio could be 1:1, or 4:1 or something else and that's a matter for the designer that doesn't particulary concern the user.
Yes, it provides a demonstrable improvement in immunity to impulsive interference, especially if the downlead goes through the loft near to mains wiring. To pass the CAI & DTG's 'benchmark' tests an antenna has to pass a 'feeder pickup' test, whcich amounts to a test of the effectiveness of the balun. See
I like that. Lots of "throbbing DSPs" in a DTT receiver, to use a phrase coined by an acquaintance of mine, who posts here occasionally.
IFFT for the COFDM demod, soft-decision Viterbi and Reed-solomon FEC decoding & then MPEG decoding. Try doing all that with valves (he said, being half-way through reading Gerogina Ferry's book about LEO).
Interesting - I think I first heard "one foot per ns" from somebody at Mullard; I didn't know there was connection with Ms Hopper. Didn't she invent the concept of the compiler?
That's how its currently used for UK DTT. Another application is the 'single frequency network' concept used for the national DAB multiplexes. This depends on having precisely synchronised transmitters (done using GPS for the timing, I think) all radiating the same stream, and, obviously, a longer guard interval -- 246us for Mode 1 DAB (the mode used on Band III). From the receiver's point of view there's no difference between a reflected signal and one from another synchronous TX. Clever innit?
OK, sorry, but that wasn't clear from what you said.
It should and does give good multipath performance, up to (a little over) the guard interval. As we're not using SFNs for TV the guard interval fraction has been set to the lowest DVB option (1/32) to minimise the loss of capacity.
ISTM that you're thinking more here of the choice of modulation constellation and code rate. In 1998 DTT launched with 64-QAM modulation &
2/3 code rate, giving about 24Mb/s net data rate. Following the demise of ITV Digital the BBC and Crown Castle decided to opt for 16-QAM to increase robustness, but to reduce the code rate to 3/4 to claw back some of the lost capacity. This combination gives about a 4 dB advantage in a gaussian channel. So we now have a hybrid situation with the BBC & CCI running 16-QAM 3/4 (~18Mb/s) but with the D3&4 mux (ITV, C4, etc.) and SDN (C5, S4C, etc.) still running 64-QAM 3/4.The higher BER there might just be due to the signal being weaker, of course, or to long-delayed echoes.
I think most aspects of it are now pretty well understood and measurements agree well with theory. The performance of different receivers in the presence of long-delayed echoes does vary though, and depends (IIRC) somewhat on the Viterbi implementation. Unless you can be more specific about which of Jonathan Stott's papers you're referring to I can't really add any more.
That's a completely separate issue, not COFDM related. There isn't, AFAIK, the same flexibility as there is in DVB-T to change the transmission parameters to trade off capacity and signal robustness.
I don't think she's the one we thank for compilers: early FORTRAN beat her to that punch. But we do have her to thank for COBOL (I presume you know the one about its Stroustrup-analogue object-oriented follow-on, ADD ONE TO COBOL. ?) And the story goes she used to enliven her public talks by handing out 'nanoseconds' - one-foot lengths of copper wire.
You've answered the follow-up question I stopped myself from asking! Couldn't immediately see how the DAB network would cope given single-frequency transmission with the maths working out as for Freeview, but wasn't curious enough to either think through the obvious answer of "much longer guard interval", or to ask. And here it comes, unasked for but no less gratefully received ;-)
Cheers, Stefek
Well it was 3ns a meter by the time I got into a proper electronics lab.
We even took a 100meter reel of cable, and shoved a pulse generator on it to check
The reflection did take about 600ns to come all teh way back..
You sure about that?
I assumed COBOL predated Fortan.
No. Fortran (FORmula TRAnslation) was the first high level language, well 3 GL. COBOL was in 1959. It was a temporary measure that they expected to last no more than 5 years.
Correct. Lisp and Algol predated Cobol, too.
Nostalgia: I used to be quite proficient in Algol 60; never could understand why anyone could prefer Fortran...
I think it was most of all availability of libraries/bits of program others had already written: an early case of first-to-market wins.
I too have a fondness for Algol 60: the first program I ever wrote, doing self-teaching on the University (of York, if anyone's interested) timesharing machine was in Algol-60, a few days after I'd got my account and got fatally bitten by the computing addiction while nominally doing a biochem degree (swapped to CompSci after a year). A little automated Q&A system recommended which language you should learn, and though it had been put together by Simula fanatics - so Simula was always somewhere on the top 3 of its recommendations - Algol was wot floated to the top, so I hied me off to the university library, got out a book, and started on the slippery slope. Deepening the addiction, the 6-line program compiled & ran first time...
Ah, TOPS-10: now *there* was an OS. And a 36-bit machine with ability to address bytes of arbitrary size (from 1 to 36 bits) and step within and across words as you incremented along... and perform arbitrary levels of address redirection (briefly opening up the possibility of an uninterruptible instruction, JRST @. - causing the machine to fetch the address of the address of the address of the address of [repeat ad inf] the place to jump to.
Stefek 'has this drifted off topic far enough yet'?
Another factor was that a lot of UK universities bought Elliott 803s, mainly in the 60's IIRC, and then followed by buying 4130s. University of Wales had one of those, and I believe York and Manchester did as well.
Algol-60 was the preferred compiler on both of those. On the 803 you had to load the compiler from paper tape (about 4k of it) and then your own stuff. On the 4130 you would type up cards on a punch and give a stack to an operator. At some time later, you would get a stack of cards back and some listing.
Mentioning York, reminded me, since we were discussing mail the other day, that there used to be a device invented at York called a 'York box". IIRC, it was some kind of mail gateway or perhaps protocol translator. They sold units to most of UK academia. I can't find any references to it now though...... I think it was early 80s?
.andy
To email, substitute .nospam with .gl
I was taught by one of the men who formed Algol, and another who developed the LCD display.
"C" beats em all. operating systems have been written in C.
.. and who were they?
.andy
To email, substitute .nospam with .gl
lecturers of course. duh!!
In trigonometry, no doubt... obtuse angles.....
.andy
To email, substitute .nospam with .gl
They have obtuse angles in trig there days? My oh my!
That's all that should be written in C, in my book (and there are better languages for that). And even then only by people with at least 0.9 of a clue.
You obviously don't know about C. The problem with C is that if the programmer is not educated to write structured code it is awful and spaghetti like. Pascal is the best language to learn from as it forces the user into a reasonably structured way. Write all languages like in Pascal and you can't go wrong.
C is a programers language. It is for getting your hands dirty.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.