The maximum number of converters & modulators useable together?

[DoctorWho]

I have no intentions of doing this, and so the question is only theoretical, but it is something that I have thought about and wondered how possible this would be?

I've often thought how nice it would be to have a small hotel or guest house with a vintage theme, for example, a floor standing dolls eye switchboard with manual telephones in every room where the switchboard is manned by an operator and all calls are put through, similarly each room is suppled with a telephone, say a 300 or a 200 with a dummy dial, and perhaps a valve radio.

I had also thought about televisions. It would not be difficult to obtain a variety of 50's and 60's TV sets with 13-channel turret tuners, then there's a question of programmes.

What would be involved in using 13 Aurora converters, side by side, each one set to a different channel, starting from 1 and going right through to 13, and each channel relaying something different, for example BBC1, BBC2, ITV, Channel 4 and Channel 5 could be put through on various different channels, perhaps Channels 1 and 9 could be used again for BBC1 and ITV, then of course a few Freeview or Sky channels could be set down different channels and also some archive footage/recordings, old films and the like sent down others.

Of course I realise that a separate DVD player/Freeview/Sky box etc would be needed for each and every converter, but how would you go about setting something like this up so that all 13 channels could be used without causing any interference to other channels.

Is there any reason why this would be impossible? If so, then what would be the absolute maximum number of channels that could be used in Band I and Band III in this kind of arrangement without causing any interference to each other, and what kind of set up would be required to combine the output from all 13 (or the maximum number possible) of the Aurora converters and then send all of the signals around a building using standard distribution amplifiers?

The idea would be so that each person in each room could turn on their 405-line set and go through the 13 channels (or the maximum number possible) to select from a variety of modern or vintage programmes, and watch it all in 405.

As I say this is only theoretical, I have no intention of doing this, but I would like to know what would be involved and also if all 13 channels could be used at once, or, if not, what the absolute maximum number of channels would be that could be used at the same time, side by side, going down the same co-axial feed around a building.

If nothing else, it would be fun to try!

All the best,

Peter.

[Brian R Pateman]

Hi Peter,

Thirteen modulators each tuned to a different channel should work using a good quality distribution amplifier. All the amp has to do is be a broadband amplifier and provide some rudimentary isolation and impedance matching for the various outlets. One of those period Labgear ones would be good and bring back fond memories as I installed loads of them many years ago.

Obviously the modulators would be more of a problem to source. They should be easy enough to build though.

All valved modulators? Think of that, a 19" rack loaded with thirteen (Make it 15 so you could have a couple of "hot" standby units) modulators with nice glowing valves. Should cut down on the heating bills too!

I think it's a lovely idea - I'd come and stay at a guest house like that, when are you taking bookings?

Regards,

[JoshWard]

That would be a nice idea, but surely you would never want to leave?

[ppppenguin]

With most modulators (including Aurora) you would want filters after each one to remove harmonics that could interfere with other channels.

I think you will find that most TVs will not take kindly to having signals on adjacent channels. The selectivity is generally not that good.

[Ray Cooper]

It's a lovely idea... but with potential snags.

a) Let's start with the biggest. If you have a straightforward modulator running on, say, channel 3, then the natural output from that modulator will be double-sideband. This means that most of the (unwanted) upper sideband of Ch3 will overlap the signals from your next channel, Ch.4, and cause severe interference to both vision and sound in that channel. Likewise your Ch.3 signal will be being interfered with by the unwanted sideband from Ch.2. The same goes for all channels except Ch.1 (which is a genuine double-sideband allocation channel, so won't interfere with Ch.2): Ch.6 which doesn't have a channel immediately below it since it's the first channel in Band III and so won't be interfered with but will interfere itself with Ch.7: and Ch.13, which has no channel above it to interfere with but will itself be interfered with by Ch.12. (Whew).

b) Bear in mind that even with proper vestigial sideband channels, earlier 'fifties/'sixties sets may suffer some interference from adjacent channels. Okay, all IFs have filter notches to remove lower-adjacent vision carrier and upper-adjacent sound carrier, but most of them may only work satisfactorily when the interfering signal is quite a bit lower in amplitude to the wanted signal - as would be the case where the interfering signal comes from a more distant transmitter. Any receiver not using a SAW-filter in the IF (ie, sets made before the 'eighties) is likely to give some problems. In your setup, all signals will be more or less of the same amplitude, and the adjacent-channel suppression may not be good enough to stop problems, buzz on sound and sound-on-vision being the most likely effects.

c) You are going to be running a large number of channels all at comparable levels through your proposed distribution amplifiers, so the possibility of cross-modulation between the carriers exists.

d) There is the non-trivial problem of just how you are going to combine thirteen channels onto a single feeder, whilst preserving the isolation of modulators one from another. If the cross-insertion loss between modulators isn't high enough, energy from one will appear at the output socket of another, and again cross-modulation will result, giving patterns, buzzes etc.

So it pays to be modest. To cure a), you will unfortunately need vestigial sideband filters for each channel - a daunting prospect. However, you can cure a) and b) at a stroke by only using non-adjacent channels, e.g. 1,3,5,6,8,10,12. That only gives you seven channels to play with, but as a bonus will ease the problems with c) very considerably.

As to d) - well you're on your own with this one. The simplest solution would be a straightforward star combiner - but this will lose you a lot of signal and produces little cross-insertion loss between modulators. A 'proper' combiner using channel-pass filters would cure the problem but add a lot of complexity, as well as being very non-straightforward to set up.

What's the solution? Start with a small number of channels and then keep loading 'em on until problems show up. It's next to impossible top predict when this will occur, it depends so much upon your configuration.

Undoubtedly your big problem is going to be sourcing components such as filters - Band I/III gear is difficult to come by in this country - anybody know of a source?

But then it's only a pipe-dream, isn't it?

[ppppenguin]

I bow to Ray's extensive knowledge of transmitter issues. I admit I'd totally forgotten about the DSB/VSB problem.

The old ILEA schools cable TV system used several adjacent VHF channels for 625. It was a closed circuit system so the channels may have been spaced further apart than usual. It worked OK so I suspect the specially made Decca receivers had unusually good adjacent channel rejection.

[Steve_P]

Lovely idea. Ray is spot on with the advice though. I'm sure old filters can be made and obtained if needed!

First of all, don't use adjacent channels. Not worth it. Five is a maximum, six Maybe. Leave Sky out of the equation. Use say..

Band I...

1 - BBC1.
5 - BBC2

And on Band III...

6 - ITV
9 - Ch4
12 - Ch5.

Filters on every output, keep the levels as low as you can.

There may be a channel you could use for an Internal Feed for period programming, maybe not. Try a quiet channel and then go round all the other channels, making sure picture and sound are OK.

Sets themselves have to be reliable. 1400s, although not 50s, would be ideal. A good 50s set to use would be the Philips Set that everyone seems to like - the 21TG100U. You don't want sets breaking down on you....

Radios - why not have an internal station broadcasting period music?

The idea of a room full of valves is nice, but frankly it's a no-no. Use Auroras.

Oh, and make sure your phone desk is suitable before you connect it up...

Hope this lot helps!

Cheers,

Steve P.

Awaiting the opening day...

Ray : Band I and Band III stuff - I know someone who does things like this. Ships TV Transmitters all over the world, even America.

[Brian R Pateman]

Rats!

Like Jeffrey I'd forgotten the DSB/VSB issue - carried away with the beauty of the idea!

I had only suggested thermionic modulators, not a replacement for the Auroras, there must be some concession to practical modernity.

The "in-house" radio station is a nice idea.

When it comes down to basics I am on record as the man who refused to stock and sell anything to do with satellite T/V because I was convinced it would never catch on.

Who wants more than the four channels of rubbish we had in those days? I couldn't conceive that the general public could be dumb enough to need more than that!

So Steve has it about right with his channel provision.

(Although as a Pye man I'd go for 17" Continentals).

Regards,

[Steve_P]

I've just looked at the frequencies of Band I. The internal program is best suited to Ch 2.

I've got some cable TV bits here somewhere by the way. You'll need an amp and of course good quality cable and connectors too.

Cheers,

Steve P

[arjoll]

No problem getting band I and III stuff in NZ and Aust (and probably any other country still running TV on VHF). My first reaction was the DSB/VSB issue - I know basically all systems here avoid adjacent channels, but remember reading a few years ago about achieving it using good VSB modulators with adjustable output for both sound and vision, and dropping back the sound carrier quite a bit. This was system B though, with FM sound, so I'm guessing things would be different with AM, and also would have been written with more modern TVs in mind.

In terms of combining, Hills do some active combiners that could suit. Lincrad do some directional couplers as well. NZ's VHF band doesn't go down quite as far as the old UK one (channel 1 here is 45.25 vision, 50.75 sound) but 1 MHz lower than Australia channel 0.

[DrZarkov]

Cable TV in Germany is done on VHF only. For parts look at the german companies like Zehnder, Astro and Technisat.

[DoctorWho]

Thanks for the input on this, it is indeed, sadly, only theoretical, if only it were possible!

I already have an in-house Medium Wave transmitter (Gizmo) which radiates vintage radio recordings back on to Medium Wave, so that would easily be sorted. We also share the bedroom with a floor standing dolls eye switchboard which is fully working and connected up, there are also probably enough old telephones in the house to set up a pretty good network.

My TV collection, however is 1936-50, I don't collect post-1950 sets, so I'd have to source some more "modern" sets, say 1955-1964 to keep everything 405-only.

I did wonder if there would be issues with overlapping/sideband issues, so I can see the possibility of problems here. If very precise filtering were used to cut out all harmonics and excessive sideband then I wonder if it would be possible to transmit on all 13 channels at once, or would, as discussed above, 6 be the limit? Even with 6 this would allow all 5 terrestrial channels to be relayed plus another channel of vintage footage. Somehow I'd personally want to have the vintage footage on Channel 1 as though it were coming from Alexandra Palace - if things really took of then theme nights may be possible where Sylvia Peters could be employed for the evening for in-vision continuity. Then we could have interludes and so on - the real vintage television experience!

Of course this is indeed just a pipedream, but it would be superb to try. If I'm ever in a position to do this then I certainly would, but I can;t see it in the foreseeable future, if, however, the chance ever arises then I'll enlist help from as many on here as are willing and then have a free theme week of vintage radio and television programmes, with, of course, everyone dressed in clothing of the correct era, I guess also that, under such circumstances, a week's stay should also be about 14 gns.

[Brian R Pateman]

And arriving in period vehicles?

Regards,

[DoctorWho]

That goes without saying Brian!

[Andy Green]

Re: band III sources - Ireland still uses band III , and also has very high cable penetration (so that virtually everyone can recieve British or Northern Irish TV)

Most cable systems use all the frequencies from Band 1 all the way through to UHF (the non standard in between channels are called 'super or cable' band)

Taylor Brothers of Oldham probably have all you need for doing a SMATV system, another company's products that I have used are Polytron
www.polytron.de they have an office here in Ireland, (no web site , phone 00353 52 477 4706 - talk to Louis Kinsella) and their products are quite cheap, including very useful tunable notch filters, channel equalisers etc etc.

[DoctorWho]

That's very interesting to know, thanks for this information Andy. It sounds like Taylor Brothers are a very useful company to know.

[bobsterkent]

And arriving in period vehicles?

Surely that means arriving by train or excursion coach!

[DoctorWho]

A period one of course Depends I guess, there were quite a few cars on the roads in the "turret tuner" era I believe.

[Hybrid tellies]

Interesting what was said earliar about overlapping channels. Down in west Cornwall BBC1 used to be on ch2 and ITV (or Westward) on ch12. Both were good signals but the ch2 signal would spill right across ch3 and the ch12 sidebands splash extended across some of ch11 and all of ch13. However we could still watch Southern TV from Chilerton Down on ch11 during certain weather conditions despite the sideband interference from ch12.
So here is my fantasy choice of channels
News 24 on ch1
BBC1 on ch2
BBC2 on ch5
TFM on ch6
The Hits ch8
UK History on ch10.
ITV1 on ch12
I think I would be tempted to be a bit naughty and connect some of the Auroras to rabbit ears aerials to make it more authentic. But would keep the ch2 feed to good quality coax cable to avoid the high level of interference from those wretched baby alarms on 49Mhz.

[Steve_P]

I'd thought about that, Hybrid. But the problem is where will the out of band harmonics fall? FM Radio? DAB (Please!)? Lower half of the TV band?

That's why I decided against it. Nice idea though.

Just wish he'd go ahead with this idea. It's a winner!

Cheers,

Steve P