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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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29th Dec 2012, 8:06 pm | #1 |
Retired Dormant Member
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The Future of Short Waves
I am posting this because of my increasing concern about the impending shutting down of AM transmissions in the UK. Please don't take this as the usual moan about the situation - I am asking for expert technical advice.
Preamble: I was professionally and technically qualified and active in telecommunications as a Merchant Navy Ship radio officer between 1960 and late 1992, dealing with CW, AM, SSB, FAX, RTTY and Satcoms, although my heart always lay with CW and AM (But RTTY was really extremely useful, especially on passenger ships). My question regards the future of short waves. I am familiar with the normal AM broadcast transmissions, CW morse and the radio teleprinter type modulation etc. I know that FM does not like the short waves, although I have had occasional 1,000 mile + contacts on 27 mHz FM CB from my ship at sea, but this was, as I say, "occasional." Is AM the only feasible modulation for short waves or does this digital thing work on SW as well? I enjoy making small receivers, 1 to 4 or 5 valves. I have very little interest in what I pick up on them these days as long as they work! Must I prepare to abandon the medium waves for the short waves? Is AM more or less guaranteed as the only acceptable modulation for broadcast stations on SW, or will "digital" encroach on SW as well? Bob |
29th Dec 2012, 9:06 pm | #2 |
Dekatron
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Re: The Future of Short Waves
There's already a move to introduce digital encoding for broadcast transmissions on medium- and short-wave.
http://en.wikipedia.org/wiki/Digital_Radio_Mondiale There's nothing really to prevent use of narrow-band FM in the 3-30MHz range except the somewhat-restricted range of frequencies that are allocated to broadcasting. NBFM is only really used by us amateurs in the 28-30MHz band where there's plenty of bandwidth. There are a lot of "data" modes using digital techniques now: some of these are rather impressive, giving error-free RTTY-type operation with microscopic amounts of power on a channel where the human ear can't actually detect the presence of a signal: indeed, professional very-low-data-rate types talk about noise-to-signal ratios not signal-to-noise ratios! Imagine a sonobuoy floating around in the mid-atlantic, with a 50-milliwatt transmitter feeding a 3-foot whip antenna, and giving error-free data transmission back to Australia on the HF bands. And don't forget, CW is really a "digital" mode! G6Tanuki |
29th Dec 2012, 9:18 pm | #3 |
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Re: The Future of Short Waves
I was really wondering more about the broadcast transmissions from all sorts of obscure countries. There seems very little CW on HF now, compared with the days when all the merchant fleets used it - not all that long ago.
All that I am really bothered about is whether there will be anything left anywhere of AM transmissions just to show that what I have built is working. Not really interested in picking up the cricket-chirping of teleprinters. I quite like picking up foreign broadcast stations even if I don't know what they are talking about! Probably AM will carry on for decades yet on SW, even MW, but I do still feel rather concerned about it sometimes! Bob |
31st Dec 2012, 3:09 am | #4 |
Tetrode
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Re: The Future of Short Waves
SW is finished in the west I'm afraid.
This years WRTH just has about 70 pages (about 3/16" thick !) section on international broadcasting. There's a bit of a feature on the future of HF broadcasting, with the consenus of opinion is of its use in the third world, or war ravaged countries will continue, but the internet has killed it everywhere else stone dead. |
31st Dec 2012, 3:33 am | #5 |
Heptode
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Re: The Future of Short Waves
Just a quick look here...
http://www.hfskeds.com/skeds/ ...at the B12 Excel spreadsheet zipped will show you everything on HF including some of the more interesting utilities such as the old WeFax (still going) and HFDL for aircraft. Whats more noticeable is the number of Chinese transmissions, some for domestic use, and the rise in the evangelical stations from the US. Radio New Zealand and Radio Australia are both still going strong, mainly to the Pacific Islands - but all in all - agreed that it ain't what it used to be! DRM was going to be the bees knees but need good strong signals to decode it properly - IMHO it will die a natural death. I was a 'sparks' too, in the good ole' days of the 60's for Marconi but left to start work with the UK CAA then over to NZ for CAA then AirNZ - still playing with radio - old , new and in-between!
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31st Dec 2012, 9:44 am | #6 | |
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Re: The Future of Short Waves
Quote:
Another problem with SW is PLT, those through the mains networrk things, they use 3 to 30 (sometimes 300) MHz down mains cable, most leaks out ruining reception for about 50 yards or more. |
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31st Dec 2012, 12:55 pm | #7 |
Dekatron
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Re: The Future of Short Waves
Correct. By 2014 it'll have gone the way of steam trains, sailing ships and going to church. DRM (Doesn't Really Matter) was ten years too late.
HF broadcasting seems to be on the up in China, however.
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31st Dec 2012, 4:59 pm | #8 |
Octode
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Re: The Future of Short Waves
I wrote this in 2007 for a non-technical audience for the BBC, amongst others:
http://mt-shortwave.blogspot.co.uk/2...challenge.html I'm now pretty sure DRM for HF (and MF/LF for that matter) is more or less dead in the water, at least for the developed nations where 3G/4G etc. will eventually have the coverage of VHF/FM. But of course it won't be free like tuning in a radio is! (Very nearly all stations using SW are available via the internet, along with many thousands of much more interesting podcasts on any subject under the sun - including SW broadcasting!) There was talk of India and China developing DRM for their domestic broadcasting once the cost of the radios comes down. But even if the radios only cost £1 each to buy, that's still £1 more than the one they already have that works well enough as far as the public in these countries are concerned! I think we'll just have to get used to the ongoing decline of short-wave broadcasts, although they may continue their role in domestic broadcasting for some time in South America, Africa and Asia. Regards, Ian |
31st Dec 2012, 6:01 pm | #9 |
Octode
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Re: The Future of Short Waves
Is there anything to stop small. commercial or non commercial, stations springing up to fill the gaps? In the way we now have lots of local MW stations? I would guess that the barrier might be licensing and fees, but it seems an opportunity, and amateur clubs would have the expertise?
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31st Dec 2012, 6:08 pm | #10 |
Heptode
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Re: The Future of Short Waves
Is the internet really that ubiquitous nowadays? I can remember in the 70s and 80s working in the Niger delta area that a lot, if not most, bush villages did not even have electricity and I doubt if that has altered much. Memories of great big radiograms run off banks of D cells! And great jubilation when we moved into a village for a few weeks as we had the white man's magic electricity - lights on all night long.
In those days every village had one or more domestic short wave receivers run off more D cells. The World Service was highly regarded as a source of "real" news not what the local government wanted their people to believe. I would be very surprised to learn that such places were now on the internet. Gordon |
31st Dec 2012, 6:15 pm | #11 |
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Re: The Future of Short Waves
Thanks for the replies. Since starting this, I have searched on Google and all the experts seem to be agreed that SW will all be gone in couple of years. That gives me great reason for hope. As soon as The majority of experts say something is certain, it appears that it is not certain, at least not in the foreseeable future.
When I first went to sea in 1961, a number of my shipmates gleefully told me that radio was on its way out and before 1970, we would all be redundant. By 1970, communication with anyone on SW still needed considerable skills and morse was still the most common form of communication at sea. Still, they assured us that another five years would see it out. By 1980 we were still going strong and morse was still king, but HF teleprinters were becoming more popular. All that happened with them was it became so cheap and easy that the attitude changed to "why use ten words when a couple of hundred will do just as well!" So the operating side got easier, but mountains of paperwork and typing were generated. After the Falklands, satellite communications came in that was really easy (as long as it worked). Still managed to get another ten years out of the job and finally left because I was fed up with it, not that it had finished. It still carried on for a few years! I still enjoy repairing and designing valve radios from time to time, but would not like to think that there will be nothing to pick up after next year. I haven't listened to SW for some time now, but today, got an old Regentone ARG359 out of the attic and started on a repair. It has SW from 6 to 18 Mhz, so I will soon be able to hear for myself! Bet it goes on for donkeys years yet! Bob |
31st Dec 2012, 6:17 pm | #12 | |
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Re: The Future of Short Waves
Quote:
I've been heard to opine in other fora that truly the best thing about the coming of 'DAB' digital-radio is that it provides a vehicle to clear traditional corporatist broadcasters from Band-II for subsequent repopulation by the independent/free-radio/pirate-operators. G6Tanuki |
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31st Dec 2012, 6:18 pm | #13 |
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Re: The Future of Short Waves
Well, I do hope that happens!
Bob |
31st Dec 2012, 8:51 pm | #14 |
Octode
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Re: The Future of Short Waves
Well I expect AM broadcasting on MW and SW will continue for some time, but as I said above, in the developing world as the internet is still not widespread in these nations.
I'm not sure what will happen to MW in the UK once it has been left to go 'fallow'. The big broadcasters know it's hardly worth their while being there since the levels of man-made interference has risen significantly over the past decade or so, and the multi-kilowatt transmitters (with dwindling audiences) cost a fortune to run. The fact that synchronised groups like R 5 Live, Virgin, etc. are no longer synched suggests the broadcasters now don't consider it worth investing in good engineering practice - causing a decline in quality, causing a decline in listeners, etc... I think the national networks on FM are expected to migrate totally to DAB in future (not 2014 as had been suggested). When that happens large chunks of band II will be clear for small licensed commercial/community broadcasters to move into. As for MW, well, I don't know... More community stations and RSLs may use it, but since band II will have lots of space they'll want to use that instead for better sound quality, easier and cheaper transmission systems, no interference at night, etc. etc. It's not as if MW can be flogged off for 3G/4G, so perhaps part of it will be left for amateurs to use, or low-power, lightly-regulated community stations. Do we have any Ofcom insiders on the forum who can hazard a guess? Regards, Ian Last edited by Ian - G4JQT; 31st Dec 2012 at 8:59 pm. |
1st Jan 2013, 12:02 am | #15 |
Dekatron
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Re: The Future of Short Waves
Even if all SW AM broadcasts disappear - which I doubt will happen soon - it must be possible to build a SW 'pantry transmitter' to give our vintage radios something to hear on SW.
A medium-wave pantry transmitter, set to the bottom end of the MW band around 190 metres and adjusted to output plenty of harmonics, should also be audible within the 49m band (4th harmonic), 41m band (5th harmonic) and possibly 31m band (6th harmonic).
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1st Jan 2013, 4:19 am | #16 |
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Re: The Future of Short Waves
Digital modes like DRM work really well in theory providing you have a good receiver with wide dynamic range and a good antenna and earth (earth being the reference end of the antenna of course). DRM was designed to overcome multipath fading and Doppler shift. At the transmitter several digital "coding profiles" can be used depending on the target audience.
mode A for local transmissions with little or no multipath, mode B for medium range transmissions with mutipath, mode C for longer range multipath and some Doppler, mode D for very long range lots of multipath and Doppler. I think most of the DRM broadcasts in Europe use modes A or B and target local or regional audiences so you won't get good reception if there is severe multipath or Doppler for mode A or B. DRM receivers take a long time to re-aquire a signal once they lost sync. Under severe fading (multipath) conditions you might loose a few seconds of audio with an AM transmission and your brain will fill in the missing gaps, a DRM receiver on the other hand may take tens of seconds to re-aquire the signal. With fairly good propagation conditions but lots of noise you brain will filter out the noise in an AM transmission but a DRM receiver will jump in and out of lock. Just to make matters even worse, consider a typical consumer DRM receiver, a plastic box with a wall wart for a power supply and a telescopic antenna. Now you have a receiver with a high impedance electrostatic E field antenna using who knows what for an earth or antenna reference. They won't pick up AM transmissions let alone digital modes. I happen to be the unlucky owner of such a receiver manufactured by a company that should have stuck to making toasters! My DAC90 picks up less interference . If receiver manufacturers used magnetic loops or wide band ferrite antennas then DRM might have a future but if current design trends don't change then poorly designed receivers will kill off DRM. Chris |
1st Jan 2013, 10:41 am | #17 |
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Re: The Future of Short Waves
A shortwave pantry 'modulator', never thought of that. Soldering iron time I think.
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1st Jan 2013, 11:27 am | #18 |
Heptode
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Re: The Future of Short Waves
A shame DRM didn't take off, the experiments on 26MHz for localised transmissions were particularly interesting. But it will never take of in the third world due to the amount of power consumed by the decoders. When a set of AA batteries is ore than a days wages this will always be the case.
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1st Jan 2013, 12:11 pm | #19 |
Dekatron
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Re: The Future of Short Waves
Quite correct, Jonster. Most of Skelton's remaining AM transmissions are aimed at west, central and east Africa, with a couple of DRM transmissions aimed at Europe.
It isn't just the cost of running the receivers (no 'wind-up' DRM radios yet as I can make out), it's the cost of running the transmitters. Every year requests are made to improve efficiency and use less energy. HF broadcasting will only continue if someone is willing to pay for it. The god-botherers seem to have a bob or two to spend on it, but even they are cutting back. The days of broadcasting one's own political ideals and agenda are gone in the west. HF broadcasting was never an entertainment medium: it was a political one. You can get faster internet access in West Africa than you can up the Eden Valley in Cumbria. Incidentally, Skelton celebrates seventy years of broadcasting this April 25th.
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1st Jan 2013, 1:21 pm | #20 |
Dekatron
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Re: The Future of Short Waves
You are no doubt right Russell, the old technology is cumbersome and expensive in relation to the www. It wasn't so long ago that questions were being asked about how the undeveloped majority of the world could possibly be wired up. The answer, of course, was that they wouldn't be. Not only is Satellite and Mobile phone technology filling that gap whole new ways of thinking and doing business etc have opened up and this can only expand further with a subsequent demise of the hardware that has been vital up until now!
A forum member told me last year that he comes out of retirement to advise on TX arrays because the knowledge/experience just isn't there! On the other hand, whilst the SW network was undoubtdly a product of political action it could be argued that the arrival of mobile phone /computer is a more democratic and empowering developement. If "enough" people hear something over the web I'd suggest that it would spill over into being a broadcast. It's almost the same physical action with a computer to switch on and "tune" in as with a radio set, in the end. There's an advantage that it's also possible to measure the audience directly, as it was suggested is done with I-Player in the Telegraph yesterday. Phil's SW Pantry TX "harmonica" idea is a good option and there are of course many many designs for a Tx in the AM SW mode or bits of kit that I presume, with my limited ability, could be modified. Some gear even has an IF that falls in the SW range, as with the front end convertors that used to be built for various purposes long ago. Another issue that come to mind is that of suitable material. On MW there are always archives of programmimg around, music on 78's etc. What about the SW material that Forum members will have listened to over the last 50 years or so. Is that available or even the limited broadcasts still going out?. Do we need to start collecting those as well? I'm guessing that a lot of early SW stuff will be American in origin but I'm not really sure. I recall listening to a New York station on SW in the sixties to literally pickup " the US charts on a Saturday morning. I also used to monitor Gander but that was usually less entertaining. I think that the VOA thought itself more upbeat than Radio Moscow but not to an English teenager. Dave W |