How much electricity does a transmitter use?

radyag · 09/09/14 - 09:18

I see on digit UK that the 80 main transmitters are broadcasting at 100 kw, the old analog was 500 kw. Now at that level why does it not melt?

lundavra · 09/09/14 - 09:39

Those are maximum ERP figures not actual RF power out of the transmitter.

spiney2 · 09/09/14 - 10:35

crystal palace currently 200 kw per freeview mux (single transmitter). which is indeed one fifth of previous output power as digital tv demands. i should think this still requires output tubes and water cooling. but i dont know. if parallel solid state outputs then connecting them together to a single aerial would be difficult.

this is a big electricity saving. and the efficiency will be higher than before but again i dont know what exactly .......

smaller transmitters will be entirely solid state with air cooling. solid state is more efficient. perhaps 80 - 90 % ......

spiney2 · 09/09/14 - 10:39

big transmitters including analogue tv are water cooled. the output tube anode has water pumped through it ........ if u look up droitwich - the bbc r4 long wave transmitter - then i imagine there are pictures ....

spiney2 · 09/09/14 - 10:42

all that electrical power going "into the ether"! then diluting in power density as it travels outwards ........

lundavra · 09/09/14 - 12:13

spiney2 wrote: »

crystal palace currently 200 kw per freeview mux (single transmitter). which is indeed one fifth of previous output power as digital tv demands. i should think this still requires output tubes and water cooling. but i dont know. if parallel solid state outputs then connecting them together to a single aerial would be difficult.

this is a big electricity saving. and the efficiency will be higher than before but again i dont know what exactly .......

smaller transmitters will be entirely solid state with air cooling. solid state is more efficient. perhaps 80 - 90 % ......

Again that will be 200 KW maximum ERP, not RF power.

You are being VERY optimistic on efficiency of solid state transmitters.

radyag · 09/09/14 - 12:27

lundavra wrote: »

Those are maximum ERP figures not actual RF power out of the transmitter.

So how much electricity is used in kw per hour to gain 100 kw erp?

spiney2 · 09/09/14 - 12:28

well .... whether water used depends on the actual power output. difficult to say from erp unless you have exact aerial details ........

wikipedia claims some broadcast transmitters approach 98% efficiency ! I dont see how this is physically possible. assuming straighforward power out/power in. surely not effective erp out, a silly mistake ?

spiney2 · 09/09/14 - 12:33

i cannot find straightforward efficiency info about current tv transmitter. so lets be more general. i would say that at best a class c output stage for analogue would be about 60 percent efficient ..... probably less after harmonics filtering ....... also assuming NOT standard am output with unwanted sideband dumped into a dummy load .......

spiney2 · 09/09/14 - 12:34

freeview im not sure. since the output waveform is directly synthesised, instead of modulating a carrier ........

chrisjr · 09/09/14 - 12:36

Most manufacturers data should show efficiency.

For example this Rohde & Schwartz transmitter is claimed to reach 42% in digital mode

http://www.rohde-schwarz.co.uk/en/products/Broadcasting/TV_Transmitters/THU9-|-Overview-|-100-|-11083.html

spiney2 · 09/09/14 - 12:39

well that would be neglecting antenna losses .....

spiney2 · 09/09/14 - 12:48

40 % seems a bit low for direct waveform synthesis ...... even assuming a tube output amplifier .....

spiney2 · 09/09/14 - 12:57

"joker in the pack" is dab radio. as with all digital terrestrial broadcasting, transmitters use approx one fifth the previous power. but dab receivers need several times the power of fm receivers cos of all the digital processing chips ......

Hey there!

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