RTS turn off

[Harry Bloomfield]

I have seen it claimed elsewhere that there are companies who can "rebuild" these large vacuum tubes when they wear out/fail.

Now, that, is certainly a possibility. I think DNJ thinks these things, are similar to what he sees in the back of his old TV. These are massively bigger, and liquid cooled.

Here is one of the earlier of the two beasties... In 1988, their replacements each cost £48,000.

 

[morqthana]

As I have suggested before, the panic could have been entirely avoided, and decades ago, instead of needing input for R4, they could have made use of MSF, on 60Khz, correcting a crystal controlled RTC, using the equipment serial number, to randomise the start stop time a little.

GPS

 

[morqthana]

Slow data, 4 to 30KHz, from memory, because it is better at penetrating seawater.

Very low frequency - Wikipedia

en.wikipedia.org

 

[morqthana]

I'm just wondering what type of engineer you would ask to design such a thing, and whether they exist off the shelf.

 

[JohnW2]

Thats the rub, those in charge at the bbc likely see long wave radio, (and AM radio more generally) as something they would like to get rid of but there are various pressure groups who disagree. The BBC bosses would very much preffer to say "can't" rather than "won't" to those pressure groups as it avoids taking the blame for the decision.

Exactly.

I'm just wondering what type of engineer you would ask to design such a thing, and whether they exist off the shelf.

It only takes a small amount of Googling to find 500 kW transmitters for around 4 - 30 Mhz being offered (although I suspect they don't keep (m)any 'on the shelf'!), and I don't imagine it would take much effort to tweak such things for 200 kHz.

 

[DiyNutJob]

Here is one of the earlier of the two beasties... In 1988

Pretty sure china has bigger ones since it has to cover a bigger territory. My old 24 inch sony monitor's CRT looked about that size. I didn't have a trolley. So, I had to roll it upstairs.

 

[JohnW2]

Pretty sure china has bigger ones since it has to cover a bigger territory.

I vaguely recall that China does not have any public broadcasting on 'long wave' - only time signals and suchlike.

 

[morqthana]

Here is one of the earlier of the two beasties...
View attachment 386219

The photo in https://www.diynot.com/diy/threads/rts-turn-off.647035/post-6041545 is clearer.

In 1988, their replacements each cost £48,000.

Equivalent to £130,800 - £246,300 today.

Not that much really, (until you try to get some custom made....)

 

[morqthana]

It only takes a small amount of Googling to find 500 kW transmitters for around 4 - 30 Mhz being offered (although I suspect they don't keep (m)any 'on the shelf'!), and I don't imagine it would take much effort to tweak such things for 200 kHz.

OTOH I wouldn't be at all surprised if component values and very different efficiencies at a 1-2 orders of magnitude change in frequency meant that simple tweaking would not be possible.

 

[JohnW2]

OTOH I wouldn't be at all surprised if component values and very different efficiencies at a 1-2 orders of magnitude change in frequency meant that simple tweaking would not be possible.

I chose my words fairly badly, since I wasn't meaning to suggest that one could take an 'off-the-shelf' 4 MHz transmitter and undertake some minor/trivial 'tweaks' to get it to work at 200 kHz. Rather, I was thinking if they can make one for 4 MHz, it would only require a bit of 'design tweaking' to produce one for 200 kHz.

I would have thought that the main difference would be the size of inductors in any LC tuned circuits and the values of decoupling capacitors, but neither of those should be significant problems. I would also have thought that, in general, efficiency would be likely to increase, rather than decrease, with decreasing frequency.

 

[DiyNutJob]

I vaguely recall that China does not have any public broadcasting on 'long wave' - only time signals and suchlike.

Well their time service is on 800kw, bigger than the RTS at 500kw. China can make bigger ones if they really wanted to.

 

[JohnW2]

Well their time service is on 800kw, bigger than the RTS at 500kw.

Yes, I know that, and alluded to it in my previous post.

China can make bigger ones if they really wanted to.

I'm sure they could, as could anyone else.

 

[flameport]

Replacing components or the whole transmitter isn't the problem - both could be done.

The real problem is the substantial ongoing costs of operation for a dwindling number of R4 listeners that still insist on using LW for reasons known only to them,
and those who rely on the signals to control their storage heaters, which is a subset of the small number of homes that have RTS devices.

 

[JohnW2]

Replacing components or the whole transmitter isn't the problem - both could be done.

Quite so.

The real problem is the substantial ongoing costs of operation for a dwindling number of R4 listeners that still insist on using LW for reasons known only to them,

Indeed (and the initial capital costs, as well as running costs). As I've said, I feel sure that the primary issue is that the BBC really have absolutely no desire to continue the LW broadcasts, for the reasons you allude to.

There is one theoretical downside of the loss of AM broadcasts (whatever the frequency), probably only relevant in such far-fetched scenarios as 'post-apocalyptic' (or 'stranded on desert islands') ones, since trivial improvised electronics can receive such broadcasts in a way that is not possible with FM ones. Even more so, of course, with Morse Code

 

[SUNRAY]

OTOH I wouldn't be at all surprised if component values and very different efficiencies at a 1-2 orders of magnitude change in frequency meant that simple tweaking would not be possible.

The basic point about is amplifying devices tend to have an upper frequency limit: for example a 2N3055 transistor is a low frequency device with a high frequency limit around 2 MHz. Generally speaking a device with a 30MHz limit will usually be fine at 200KHz, the rest is circuit design ie:

if they can make one for 4 MHz, it would only require a bit of 'design tweaking' to produce one for 200 kHz.

I would have thought that the main difference would be the size of inductors in any LC tuned circuits and the values of decoupling capacitors, but neither of those should be significant problems. I would also have thought that, in general, efficiency would be likely to increase, rather than decrease, with decreasing frequency.

However what most don't realise is many high power audio amplifiers these days are designed to be used to 100KHz to incorporate signalling signals, indeed many large public address systems commonly use 22KHz and 32KHz to detect broken speaker cables, I know of devices up to 92KHz available 'off the shelf'. These days I see no reason why such amps cannot be designed to run as transmitters at 200KHz with appropriate design.