AM and FM and LW and stuff

[Sput]

Sorry to hijack your thread a bit here hyma, but is longwave also AM? I get confused.

[Nick Harvey]

AM is Aplitude Modulation, which is used on Long Wave, Medium Wave, some of Short Wave and various other places (like the Police when they used to be on VHF).

[Sput]

Right, that's tidied things up. So presumably there's some inherent physical property of lower frequencies that means you can't module by frequency. Is it just that the wavelengths would have to change too much for it to be practical?

[Inspector Sands]

AM and FM are 2 ways of modulating data/audio/video onto a radio signal. There are many others - CW (Carrier wave otherwise known as morse), SSB (Single side band), COFDM (used by DAB), QAM (as used by DTT). http://en.wikipedia.org/wiki/Modulation

LW, SW, MW, VHF, UHF etc are parts of the electromagnetic spectrum. Frequencies, from light to sound are classed into different sections for exampe Long Wave is between 148.5 and 283.5 kHz, VHF is anything between 30 MHz and 300 MHz. http://en.wikipedia.org/wiki/Electromagnetic_spectrum

There isn't a really connection between the type of modulation and the frequency that it's used in. Although some frequencies are more suitable for certain types of modulation or type of service you want to transmit. A good example of the difference between modulation type and frequency is the current block of frequencies used by TV in the UK:

In the UHF TV Band there is
AM (the modulation system carrying analogue vision signal)
FM (the modulation system carrying the analogue mono sound)
QPSK (the modulation system used to cary NICAM stereo sound)
QAM (the modulation system carrying Digital TV)

TV was broadcast in the VHF band for many years, it was also once transmitted in the MW band (in the early days of Baird's TV system) and is still transmitted in the SW bands as SSTV - slow scan TV, which as it's name suggests is slow!

[marksi]

(TV is still broadcast on VHF in the Republic of Ireland; as a result Northern Ireland only has two DAB multiplexes.)

[Inspector Sands]

(TV is still broadcast on VHF in the Republic of Ireland; as a result Northern Ireland only has two DAB multiplexes.)

The US use VHF for TV too of course, not sure if they will be after switchoff in February though?

[remlap]

and is still transmitted in the SW bands as SSTV - slow scan TV, which as it's name suggests is slow!

I think a system similar to Baird's in NBTV is still transmitted over SW amateur bands once in awhile.

The US use VHF for TV too of course, not sure if they will be after switchoff in February though?

I currently believe the digital stations that have been assigned VHF frequencies will stay on them, while the ones assigned a UHF frequency will have their power boosted I think.

[timgraham]

The US use VHF for TV too of course, not sure if they will be after switchoff in February though?

I'm almost positive that Australia uses it as well - all the main television stations sit on VHF frequencies, hence their name..Seven, Nine, Ten etc. In fact SBS was known for its poor reception because of the fact that it's on UHF unlike all the others..

http://en.wikipedia.org/wiki/Australasi ... tion_table

What confuses me though is how they're supposed to fit everything in when digital radios starts here next March? Are they planning to use a different set of frequencies or something? This website doesn't seem to explain too much.

[Inspector Sands]

The US use VHF for TV too of course, not sure if they will be after switchoff in February though?

I'm almost positive that Australia uses it as well - all the main television stations sit on VHF frequencies, hence their name..Seven, Nine, Ten etc. In fact SBS was known for its poor reception because of the fact that it's on UHF unlike all the others..

http://en.wikipedia.org/wiki/Australasi ... tion_table

What confuses me though is how they're supposed to fit everything in when digital radios starts here next March? Are they planning to use a different set of frequencies or something? This website doesn't seem to explain too much.

According to that page VHF channels 0-5a will be taken away from TV and used for something else.

It is a bit confusing though, it says that DVB will use the UHF frequencies, but then says that the higher VHF channels will remain used for TV as they work in rural areas

[timgraham]

Thanks.

It could be to do with overlaps between areas - that's what has effectively limited more channels and the like from being added, particularly in areas like the Gold Coast which have radio and TV from two or three different areas.

[Markymark]

I'm almost positive that Australia uses it as well - all the main television stations sit on VHF frequencies, hence their name..Seven, Nine, Ten etc. In fact SBS was known for its poor reception because of the fact that it's on UHF unlike all the others..

http://en.wikipedia.org/wiki/Australasi ... tion_table

What confuses me though is how they're supposed to fit everything in when digital radios starts here next March? Are they planning to use a different set of frequencies or something? This website doesn't seem to explain too much.

DAB radio has been running there for some years using VHF Ch 9 and L-Band (1.4 GHz)

http://www.wohnort.demon.co.uk/DAB/australia.html