radio frequencies question

[stator vane]

it happens mainly in france, and usually in the dark hours when one is searching the newspaper for information vital to the safety of flight, but it happened in a big way last night and hence i will risk looking like an idiot and ask the question. i did a search on pprune but no response that addressed the subject that i could see.

we will be there, cruising along, minding our own business and ATC will tell an aircraft to contact them on another frequency. the other aircraft will respond and in a few seconds, i will hear them make the new call on the new frequency, but i haven't changed my frequency!!! last night i heard three different frequencies on my one frequency.

i can understand how ATC can monitor several frequencies especially at night with reduced personnel, but i cannot understand how i can hear another aircraft that is on another frequency than myself after they have left my frequency for another.

the only thing i can think of is somehow the signal is duplicated from some ground station to increase coverage.

i have heard it several times, almost always at night and never have received an explanation from any crew that i have been flying with.

perhaps will have to file this in the same box as my radar question as to what causes the big long spikes that occasionally shows up on the radar. alien invaders perhaps.

any genuine answer will be appreciated.

cheers

[HEATHROW DIRECTOR]

It's a commonly used system at ATC units with several sectors. It's called "cross-coupling". When traffic dies down the sectors are "bandboxed", or put together with one controller instead of several. However, the frequencies of different sectors are frequently published in charts so to avoid confusion, and the need to have to tell adjacent sectors of frequency changes, the frequencies are kept the same and the ground equipment is switched to re-transmit all received signals on to the "bandboxed", or "cross-coupled" channels. So, all traffic on all frequencies hears everyone else but it sounds like one channel to the controller. (Hope I've made that clear!). It means that the "usual" frequencies may be used all the time.

It also works on a permanent basis at aerodromes where ground vehicles operate on UHF but need to contact ATC on VHF. The signals received on UHF are re-transmitted on the VHF channel so everyone can hear them... and ATC doesn't have to monitor two frequencies.

As for spikes on the radar - not too sure what you mean, but interference can cause radial lines to appear. Sometimes a whole sector of several degrees will be effected. I saw it many times at Heathrow and West Drayton - once due to an American Warship off the UK coast whose radar was on a similar frequency to ours!

[Little One]

Explained pretty well above.

On our system one simply selects the freq one requires for the different sectors and then press a button marked "COUPLE" that then feeds them all in to one. If anyone tx on any other freq the call is transmitted out at the same time on all the other relays and transmittors so to allow everyone to hear. Very nice peter

Maybe some techie can explain how this little marvel actually works to band box everything altogh I'm sure its the same/similar principle of a normal VHF relay

[411A]

In the USA this is done to some extent as well, using limited remote communications outlets...which are very effective, providing good ATC communication at locations that would normally be out of contact.

I have personally noticed that coupling started in France quite some time ago...circa 1993, IIRC.

[swh]

Have heard in Australia espically late at night with light traffic about with controllers having the airspace of several times the whole of europe tied together.

With the flightwatch frequencies its not uncommon to hear people on the same frequency over 2200 nm away any time of the day.

[stator vane]

thank you

that must also explain why late at night whilst flying over the remote stretches near Split etc on the way to Taba, the aircraft transmissions at times sound as if one were in a closed hangar with a sort of echo delay.

thanks again.

back to the paper searching for safety of flight information!

cheers;

[HEATHROW DIRECTOR]

<<In the USA this is done to some extent as well, using limited remote communications outlets...which are very effective, providing good ATC communication at locations that would normally be out of contact.>>

Not sure that this is quite the same thing. In the UK we have multi-carrier transmitter/receivers, far remote from the ATC unit. Eg, for some London Control sectors the transmitters may be in west Wales or northern England but controlled from the centre on the south coast of England. This isn't the same beastie as the cross-coupling arrangement, although far remote multi-carrier stations may transmit cross-coupled frequencies.