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Long Wave Transmitter Technology

09/28/2015 6:33 AM

An article in "The Times" today discusses the imminent closure of the 80-year-old transmitter at Droitwich, UK, which broadcasts the BBC Radio 4 channel on 198 kHz with an output power of 500kW. Apparently it is too expensive to maintain, because it requires "glass valves three-feet high which nobody makes anymore".
Leaving aside the political decision as to whether it is still necessary to broadcast Radio 4 on long wave, I ask whether it is really impossible to generate RF in this waveband without using glass valves.

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#1

Re: Long wave transmitter technology

09/28/2015 6:46 AM

Of course it is. But you'd need more than a BC108 to handle all that power!

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#2

Re: Long wave transmitter technology

09/28/2015 6:55 AM

My guess is that the number of listeners has dwindled and the cost of maintenance and/or updating cannot be justified.

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#3
In reply to #2

Re: Long wave transmitter technology

09/28/2015 9:23 AM

"Radio killed a radio star" nope. Wifi, 4G, LTE killed the radio.

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#4

Re: Long Wave Transmitter Technology

09/28/2015 11:39 AM

Digital transmission will "eat" the old analog bandwidth. UK is simply following FCC path of "selling" bandwidth by "eminent domain" authority.

However, 'tis true, vacuum tubes are not being produced as before.

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#5

Re: Long Wave Transmitter Technology

09/28/2015 1:57 PM

What about stacked Marshalls?

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#6
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Re: Long Wave Transmitter Technology

09/28/2015 3:24 PM

Rock and roll!

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#7

Re: Long Wave Transmitter Technology

09/28/2015 11:09 PM

Long wave "informational" broadcasting is a things of the past. Very few people have reception equipment for it and as you state, too expensive. There are more cost effective methods available. Over in NJ there used to be huge antenna farms for this in Ocean Gate but now there is only one transatlantic cable terminating there and it is used bv the government for back up purposes.. I sailed by there this year and hardly recognized it.

The "Voice of America" used to have similar antenna farms in Wayne, NJ. They would broadcast from long wave up to HF mostly aimed to Europe and used "skip" propagation. Both of these ceased to transmit about 40 years or more. As with the British, VOA couldn't get parts anymore.

The LF, Low Frequency band, of which 198khz is in, was be used for navigation, by triangulation, but it's accuracy has been far exceeded by GPS. GPS you just turn it on and choose how you want it displayed. It can also be integrated into other equipment such as radar, fish finders, automobiles, telephones, etc.

198kHz is ancient or for specialized use only.

Good Luck, Old Salt

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#9
In reply to #7

Re: Long Wave Transmitter Technology

09/29/2015 7:04 AM

Not that I'm a sailor, but my understanding was that one of the major benefits of this transmission was to provide weather forecasts for fishermen and other coastal shipping. What are the alternatives for providing a weather forecast offshore?

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#10
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Re: Long Wave Transmitter Technology

09/29/2015 8:41 AM

At one time, before the proliferation of modern radio techniques, weather forecasts were available in the Low Frequency, LF, range. That has been replaced/supplemented by numerous other methods and frequencies. In each frequency range there are usually other methods besides voice broadcasts. These include voice, fax, text, charts, written, and several other products. For offshore the High Frequency, HF, band operating as SSB was the primary source of weather. This had limited range and depended on "skips". Range depends on the band frequency from approx. 2-30 MHz. in 8 bands.

Now the most frequently used are the weather VHF channels. These are all (WX1-WX7) between 162.400mHz and 162.550mHz. These are adjacent to the marine channels for other purposes.

There are also satellite broadcasts of the public weather forecasts. These can be used at almost every location on the earth. There are a full complement of types of forecasts in this range. Satellite delivery of the weather provides the greatest offshore coverage. Another advantage of the higher frequencies is the antenna lengths get shorter as the frequency gets higher. A half wave antenna for the HF band is about 40m (131 ft.) to 5m (16 ft.), which uses a lot of space. In the VHF band a +3db antenna is only 3 ft long, easily accommodated on an offshore boat.

In summary, the old LF range has been surpassed by many more reliable and beneficial systems.

Good Luck, Old Salt

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#12
In reply to #9

Re: Long Wave Transmitter Technology

09/29/2015 4:38 PM

phph001

Maybe of interest to you: FCC ONLINE TABLE OF FREQUENCY ALLOCATIONS. https://transition.fcc.gov/oet/spectrum/table/fcctable.pdf

It lists all frequency allocations both in the US and international. The range is from 9 kHz, navigation, up to 275 giga-Hz, space satellites and radio astronomy. Wave lengths of 33,310.3 meters (29.7 miles) and 1,090.15 microns (0.04292 inches).

Good Luck, Old Salt

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#16
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Re: Long Wave Transmitter Technology

09/29/2015 9:13 PM

The VOA once operated the very large Bethany Relay Station that was located in Butler County Ohio, about 25 miles (40 km) north of Cincinnati, along I-75. I drove by it a few times on my way to the Air Force Museum at Wright-Patterson AFB. The tore down the towers around 1997 or 1998.

A damn shame it's now gone.

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#8

Re: Long Wave Transmitter Technology

09/29/2015 12:24 AM

Since BBC R4 long wave transmission moved from 200 kHz to 198 kHz in 1988 and it lost its status as a national, easily-divided frequency standard, the usefulness has diminished.

The amount of big towers and hardware, apart from the valves which could be replaced by solid state devices, is also prohibitive unless another good reason for keeping a long wave AM service can be found. Nowadays there are so many alternative means of programme distribution that it would be hard to justify.

Some background here: http://www.bbceng.info/Operations/transmitter_ops/Reminiscences/Droitwich/droitwich_calling.htm

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#11

Re: Long Wave Transmitter Technology

09/29/2015 2:50 PM

I shall miss it when it goes, as I used to listen it on my long drives across Europe, it was there providing interesting programs, time checks and up to date news......great at night, not so good in daytime.

Also, when I started sailing in the late 50s 60s we used Consol which was a system that German submarines used in WW2 for navigation I believe. LORAN was not for normal people, too expensive....

We used I believe a long wave radio receiver, listening also to Radio 4 (I believe it was called the "Home Servive" then) and a special map like this one, but don't ask me how anymore:-

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#13

Re: Long Wave Transmitter Technology

09/29/2015 5:30 PM

Glass valves (vacuum tubes) are about the worst device for RF response, but great for handling power. Any old transistor (including germaniums) would be able to do it. You just need enough of them in parallel to handle the power.

If you really want to maintain the station, the probable easiest way would be to substitute some other type of tube that is still availabe.

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#15
In reply to #13

Re: Long Wave Transmitter Technology

09/29/2015 6:02 PM

Which brings me back to my original question - is there really no solid-state device for handling that sort of power at that sort of frequency?

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#17
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Re: Long Wave Transmitter Technology

09/29/2015 9:47 PM

Probably, but I suspect that the financial problems go far beyond valves. It simply is an unprofitable venture on multiple fronts.

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#14

Re: Long Wave Transmitter Technology

09/29/2015 5:50 PM

For decades now, the radio stations have been refurbishing vacuum tubes rather than replacing them because nobody manufacturers replacements any more.

So, when the refurbishment businesses cease, there will be NO vacuum tubes for the radio stations to use.

Maybe, some enterprising "dot.com" company should consider designing and selling "solid-state" plug-in replacements for popular radio transmission vacuum tubes?

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#18
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Re: Long Wave Transmitter Technology

09/29/2015 10:05 PM

There were two very large electronic firms that attempted to make transistor replacements for tubes during the "60's. Neither one got very far with it. Problems were the early transistors would burn themselves up very quickly, The different operations of the tube and the transistor (what do you do with all those grids of a vacuum tube in a transistor?) made circuitry very tricky and costly, There wasn't transistors that could handle the power at that time. Another problem was cooling if there was a mix of tubes and transistors in the case. An example of this was the early marine radios for the VHF band. Typical was to use transistors for all but the final stage and use a 6146 or 2 in the final. The heat from the 6146 was a problem when keyed up for a longer than usual time.

Neither took them beyond the research stages. It was obvious that tubes were a thing of the past and transistors and integrated circuits were the way to go. Especially money wise. There now are semiconductors that will handle most high power applications when used in multiples. Typically, now a 2n3055 at 115 watts costs less than a dollar.

Good Luck, Old Salt

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