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"Plus, an article in The Guardian in 2011 claimed that only a small number of spare valves were still available for the transmitter." What a pathetic argument!
by hilbert42 2y ago
"Plus, an article in The Guardian in 2011 claimed that only a small number of spare valves were still available for the transmitter."
What a pathetic argument! When you read crap like this you know you're being told sop—an attempt to bamboozle the public with technicalities that don't really exist. Any commonly available high powered RF tetrode from an FM or TV station would do the job albeit with some (mostly mechanical) modifications to the transmitters. Also, it's a common practice to refurbish high power transmitting valves, there are companies that specialize in doing it.
I say that as someone who has been involved with high power broadcasting transmitters, in fact I was involved in building several FM broadcast transmitters from the ground up.
At only 198kHz—which is somewhere between one 1/500th and 1/1500th its normal operating frequency—any high power VHF transmitting tetrode would be just loafing along.
No doubt the way commerce works getting a one-off specialist job to do the conversion would be expensive (I wish I could do it, I'd quote half the price and still make a handsome profit).
If the BBC is so strapped for cash perhaps it could ask the Amateur Radio fraternity to mod the TXes for free as a public service. Then after the mods the service could recommence on half power to save costs.
Also, there are good strategic reasons why this transmitting infrastructure should be kept operational on these low longwave frequencies which I haven't got time to address here.
Suffice to say, I think this proposed closure is more a hatchet job by accountants than from any long-term strategic thinking by governments.
Damn shame governments only seem to listen to nanny goat advisors these days.
- bilegeek 2y agoI agree it's 99% ridiculous, but to play the devil's advocate: modifications could require re-certifying the transmitter due to regulations, which might make them not financially worth it after the remaining correct tubes die. Especially since regulations governing something so boutique and relatively obscure haven't probably been updated much to make stuff like this easier. (I confess high ignorance to UK law.)
- hilbert42 2y agoI've been through the certifying process for broadcast transmitters from scratch, albeit in Australia. I can tell you it's damn easy to overwhelm the petty certifying bureaucrats, especially so when you can prove your engineering mods give better performance specs (less harmonic interference, etc.) than beforehand. In fact, our bespoke broadcast TXs gave better performance than any commonly-available commercial equipment. Bureaucrats want a quite life, and when threatened with their actual names and positions being published in the press for being obstructive over nothing then they'll cave in. Remember, troublemakers in the public sector aren't usually rewarded with promotions. :-)
- Johnythree 2y agoTransmitters need only be re-certified if they are to be sold in quantity. Once-off Broadcast Transmitters need only demonstrate that they meet the relevant standards. Many of the existing LF and MF BC transmitters were effectively custom built to meet the requirements of their transmit license (for example, the radiation pattern of the antenna were often unique for each station).
- emchammer 2y agoDoes a VHF tetrode not have a lower bound on its operating frequency when operating at such a high power? Even if just an impedance mismatch at its terminals? If I had to choose between the two for broadcast radio, keeping longwave radio transmissions makes more sense than AM (MW) radio. Keep FM (VHF) for local radio and lose the IBOC/DAB.
- hilbert42 2y agoCan do, but Z is usually just a minor matching exercise. At those low frequencies it's not usually a problem. VHF tetrodes even make good high powered audio amplifiers. I've even seen them used in ultrasonics (~50kHz) when older original tubes weren't available. Re second point, best options depend where you are geographically in the world, mix of services, etc. There's lots of different mixes/requirements.