BC. From , joined Dec 1969, posts, RR: Reply 1, posted (14 years 7 months 3 weeks 3 days 2 hours ago) and read 4482 times:
VHF comm between tower and aircraft is in FM, for ATIS i can't be 100% sure but it is also FM to i think and you find it in the VHF band, sometimes even but in rare causes being broadcast on a VOR ident.
Mirage From Portugal, joined May 1999, 3120 posts, RR: 15 Reply 2, posted (14 years 7 months 3 weeks 3 days 1 hour ago) and read 4482 times:
It's in AM.
The VHF aero band extends from 108 to 135.975Mhz, while the UHF bands falls between 225 and 400Mhz.
AM is used for both VHF/UHF traffic for two reasons. FM signals coming and going to an aircraft would be subject to the Doppler effect, wich can shift them off the established communications channels. The grater the aircraft speed, the greater would be the shift. Secondly, AM mode permits all stations working the facility at the same time to all be heard simultaneously (in FM mode, only the station with the strongest signal would be heard).
With any FM scanner you can hear AM communications with no problem but with a AM scanner you can't hear FM communications.
ATIS and digital communications (ACARS) are also in AM mode.
HF communications are in SSB mode but that's other story.
David L From United Kingdom, joined May 1999, 9294 posts, RR: 42 Reply 6, posted (14 years 7 months 3 weeks 2 days 16 hours ago) and read 4486 times:
HF... I must find out more about that from you some time. I've used a Sony "world" radio (SSB) to pick up a few ATC conversations from the other side of the Atlantic (the west side) and once from India but it's very hit and miss and only at night (something to do with the ionosphere, I believe).
Mirage From Portugal, joined May 1999, 3120 posts, RR: 15 Reply 7, posted (14 years 7 months 3 weeks 2 days 14 hours ago) and read 4483 times:
You're right, it depends on good propagation conditions. We have good propagation when the ionosphere is "full" of ions (spelling?).
The ionosphere is full of ions when there's good solar activity.
The solar activity depends on the solar cycles and we are now almost close to the high point of this solar cycle wich will be about 2000 and 2001 (solar cycles have 11 years).
Here in my side, we have better conditions also at night but this is not an exact science.
HF communications are fascinating.