Why did 405 look so good?

[Terry]

With normal hearing, that is to be expected but, as I said, if you had prolonged exposure to it, as you would in your own home, I would expect the notch effect to kick in.

I do remember one set, a new Bush, that had a very loud whistle. The customer wrote to Bush about it and received a reply suggesting that they hang heavy curtains behind the set! The customer then complained to us and, after confirming our initial suspicions with the aid of a cardboard tube, we changed the LOPT, whereupon the level dropped to normal.

I wonder if Tracy's experience was based on a single set?

"... we had had the previous ... 405 set for some years ...". Our high frequency hearing diminishes with age, so perhaps particularly good hearing, a louder than normal whistle from the family TV but not so loud as to bother the rest of the family?

I wonder ...

[colly0410]

Talking about a notch filter: When I came back to UK after a few weeks in America & watching their 60 Hz TV pics I noticed the flicker on our 50 Hz TV pics, it took me a few days to get used to the change in frame rate from 60 Hz to 50 Hz & re-develop my 50 Hz notch filter. I'm going to America in two weeks time but I don't suppose I'll see any CRT TV set's as they'll have all gone to TV heaven by now...

[Richard_FM]

Talking about a notch filter: When I came back to UK after a few weeks in America & watching their 60 Hz TV pics I noticed the flicker on our 50 Hz TV pics, it took me a few days to get used to the change in frame rate  from 60 Hz to 50 Hz & re-develop my 50 Hz notch filter.  I'm going to America in two weeks time  but I don't suppose I'll see any CRT TV set's as they'll have all gone to TV heaven by now...

There might still be some in hotel rooms fed by an analogue distribution system.

[colly0410]

They did that in the hotel I stayed in in Gran Canaria last year but with an LCD set, just a co-ax lead to it. I was watching SKY news when a moped caused what looked like band 1 type interference, only SKY news was affected, I'm wondering if they were using a band 1 channel modulator & the co-ax was a bit leaky...

[BusyBee]

With normal hearing, that is to be expected but, as I said, if you had prolonged exposure to it, as you would in your own home, I would expect the notch effect to kick in.

I do remember one set, a new Bush, that had a very loud whistle. The customer wrote to Bush about it and received a reply suggesting that they hang heavy curtains behind the set! The customer then complained to us and, after confirming our initial suspicions with the aid of a cardboard tube, we changed the LOPT, whereupon the level dropped to normal.

I wonder if Tracy's experience was based on a single set?

This is bringing things back to me quite a bit. It was a long while ago and I have no old TV's so no reference to check. The notch effect did kick in I think. It reminds me about times when the line frequency was off and needed re-setting. I remember easily hearing the difference and knowing something was out. As an aside - maybe it is possible to set the line hold by ear without looking at the screen?

The same too with the loud whistle. At the time I would not have known about LOPT's whistleing but transformer buzzing was common (and a whack would cure) so maybe (we are talking pre-teens here). I do remember such whistles could be intermittant (similar to transformers so I suspected electro mechanical). It is probably the case that under normal circumstances there was no real issue, but as sets of those times were generally less reliable (at least my experience), and I was younger, issues did have a greater impression on me (note my love of valves now from my awe of pretty light in the back of our radio producing hundreds of stations then [pre school age]).

Tracy

[colly0410]

Talking about a notch filter: When I came back to UK after a few weeks in America & watching their 60 Hz TV pics I noticed the flicker on our 50 Hz TV pics, it took me a few days to get used to the change in frame rate  from 60 Hz to 50 Hz & re-develop my 50 Hz notch filter.  I'm going to America in two weeks time  but I don't suppose I'll see any CRT TV set's as they'll have all gone to TV heaven by now...

There might still be some in hotel rooms fed by an analogue distribution system.

The TV in our Orlando hotel was an old analog LCD, when I went into the menu it was working on NTSC & was set to cable channels, some channels were very bad quality with hum bars. I clicked over to OTA & had a manual search & found a snowy picture on channel 6 low band, think I read somewhere that some low power community analog stations are still running, wondering if it was one of those I was picking up? 

Had a bit of excitement one day: There was a bright flash of lightning, a loud crack, & a tree across the road from our hotel disintegrated in a cloud of smoke, there were broken off branches & leaves everywhere, I nearly needed a change of underwear, some kids & adults were screaming. The electricity stayed on though & the poor struck tree was near the overhead power lines that supplied our hotel.... Had a good time & didn't want to come home...

[Terry]

The TV in our Orlando hotel was an old analog LCD, when I went into the menu it was working on NTSC  & was set to cable channels, some channels were very bad quality with hum bars. I clicked over to OTA & had a manual search & found a snowy picture on channel 6 low band, think I read somewhere that some low power community analog stations are still running, wondering if it was one of those I was picking up? 

Must have been a rubbish CATV system or, perhaps (and more likely) a poor hotel distribution system because there is no way that you should be able to receive an OTA channel without a TV aerial!

There are very strict rules about the screening of CATV networks and they are particularly heavily enforced in the US. Their main worry is interference with aircraft communications - remember that US CATV networks are carried on overhead cabling - and the FCC can and will take action against any offenders.

From https://wiki.radioreference.com/index.ph...terference

• Does the CATV operator have to fix every leak?

Per the FCC: “During regular monitoring, any leakage source which produces a field strength of 20 uV/m or greater at a distance of 3 meters in the aeronautical radio frequency bands shall be noted and such leakage sources shall be repaired within a reasonable period of time.”

If the CATV operator determines that the leak is caused by subscriber supplied equipment, they may ask you to replace it or have them replace it at your cost. This is usually at the discretion of the Service Person present and depends on what the piece is that is causing the leak. Be aware that TVs and other components themselves have been known to cause leaks on rare occasions.

If the CATV operator cannot access a residence where a leak has been determined to originate from, they may disconnect that residence from their network until the leak can be eliminated.

[Geordie McBoyne]

Extract from the RCA book "TELEVISION The Future of the New Art
And In Recent Technical Developments" 1936

From page 343: Scanning requirements

60 scanning lines entirely inadequate.
120 scanning lines hardly passable
180 scanning lines minimum acceptable
240 scanning lines satisfactory
360 scanning lines excellent
480 scanning lines equivalent for practical purposes

This comparison assumes advanced stages of development for each of the line structures.
We may say therefore that a number of scanning lines in the immediate vicinity of 360, say 340 will give a very good performance comparable with 16mm home movie film.

So it follows that the 405 line system with it's 377 active lines can be considered as satisfactory.

Geordie McBoyne.

[Mike Watterson]

Till some months before Divis outside Belfast had 625 Tests, we only had my grandparents' cast off TVs. Maybe 3 models.
I used to check the Dual Standard Rental set each day. It had a vertical linear tuning scale for UHF 625 and the rotary channels for VHF 405. The test transmissions where FAR better quality than anything we'd ever seen on our 405 sets.
Later during 1971 to 1973 I restored/repaired quite a few 405 only and dual standard mono sets. We kept one for the kitchen and one for my bedroom. I remove the sliding part of the switch on most of the  dual standard models and soldered at 625.
I remember having to replace the UHF tuner valves on my grandparents' set twice. They stopped upgrading after 1969 / 1970 /1971 (not sure) and never got colour. Our first colour set was rented.

Not one of the 405 sets I restored was as good as the 625, and all the dual standard models were better on 625. Then Autumn 1973 I went to college and only after restored one mono 625 set for myself. I did sometimes work at service & repair of VTR, VCR and professional TV/Monitors after I left the BBC.

I think some people are perhaps nostalgic about 405, or had very poor 625? Though Divis would have got BBC2 a lot later than London. The 625 sets had improved.
I do remember AC coupling (Black level all over the place) on 405 sets and some had poor AGC, though not a problem on our exposed hillside with  a good view of Divis and Black Mountain (UTV) in the early 1970s.

The most memorable 405 only models  features (I wish I'd kept some, but impossible):
* One with photosensor to control brightness.
* A couple had VHF-FM and three biscuits for three FM radio. It took me a while to understand why you couldn't make any of them do this. I was only a teenager learning, no local technical library, no internet and little money for magazines. I knew no-one else into electronics.
* One had a cabled remote with a solenoid to advance (only) the turret and  volume.

I didn't know then about leaky capacitors. Later I discovered a library in Belfast that sold photocopies of R&TVS models  About 40 years too late I have 40 of those books.

Also 525 interlace is especially bad for film, due to 3:2 pulldown. The 640 x 480 is of course NTSC derived and the USA centric 1920 x 1080 is likely derived from 1125 line analogue Hybrid HD as used by Japan. Certainly my Dell 1600 x 1200 CRT can display 1920 x 1080 @ 50 Hz progressive with 1125 line  like settings in the  graphics card. Reduce vertical scan for 16:9

Should there never have been Analogue WS, or SD WS, that should have waited for HD. Also for most living rooms faster frame rate rather than 4K.  The WS CRTS were madness.
Should UK have waited two years and launched 625 rather than relaunching a 405 service only for rich people in the South East?
Should HD have been 2208 x  1200 (both integer multiples of 16, or 1536 x1152 anamorphic)  lines. Most transmission isn't 1920 x 1080  to save money but 1440 x 1080?
Should HD frame rate have been a choice of 48 & 96 world wide? The late 1950s early 1960s saw the ending of the need to match mains (which is STILL 50  AND 60 in Japan!). Film has been 24 and for years even mechanically doubled to 48 at projection. Much Cinema is shot digitally at about 4K and 48 fps.

I've seen some HD screens upscale 640 x480, 800x600 and 1024x768 fine. The so called HD Ready are rubbish for anything.
VHS usually looks terrible on an HD screen. I've wondered why there are only "Zoom modes" and no "1:1 pixel" modes. Still, I was given a 4K TV and though larger than our HD 42" Toshiba, it does the VHS much better. It also reduces the horizontal combs on stupid INTERLACED stored NTSC region DVDs. Most US region DVDs store the film frames at 24 fps progressive and the player does the pull-down. Our old DVD player has a progressive component output so if the screen does progressive, then there is no comb artefacts. Traditionally  "PAL" regions of DVDs simply speeded up playback 24 -> 25. Some discs later had pre-pitch fixed 5/6ths soundtracks.

So though I'd like to have some 405 sets in my collection, I don't miss the format.

[Mike Watterson]

Extract from the RCA book "TELEVISION The Future of the New Art
And In Recent Technical Developments" 1936

From page 343:   Scanning requirements

360 scanning lines  excellent
480 scanning lines  equivalent for practical purposes

This comparison assumes advanced stages of development for each of the line structures.
We may say therefore that a number of scanning lines in the immediate vicinity of 360, say 340 will give a very good performance comparable with 16mm home movie film.

So it follows that the 405 line system with it's 377 active lines can be considered as satisfactory.

They were indeed comparing with cheap news grade 16mm, or cheap duplication of 16mm for the home market and picked 441 lines, as you can't just have any number due to limitations of the timebase generation.
Similarly the H & V pixel count is best an integer multiple of 16 for digital systems.
Interlace is evil for  Digital or conversions or upscaling, however it's irresistible x2 compression for "free" on any analogue system as resolution perception is poorer as frame rate goes up and static or slow pans look nearly twice as good as simply having 1/2 the lines.

so interlaced
360 = 180
480 = 240
405 is 377 = 188.5 line

Hence CGA IBM was 640 x 200 graphic mode to allow for overscan on an NTSC TV.
EGA and VGA needed progressive scan screens.