WA Radio Scanner Users' Group

Gentlemen, a bit of info for a novice please.
Is there a different transmitter (or loaction) used for approach, ATIS and Tower?
I'm able to receive clear comms from Melborne center and it's associated channels from both planes and ground.
I live near Joondalup so I know I'm quite a long way away from the air port and one would expect pretty poor reception from the ground. But why then do some of the frequencies boom in? The only thing I can think of is that there are transmitters located at the airport sight and others that are located maybe in the hills. How close to mark am I?

Thanks all

Sol

SOL wrote:Gentlemen, a bit of info for a novice please.
Is there a different transmitter (or loaction) used for approach, ATIS and Tower?
I'm able to receive clear comms from Melborne center and it's associated channels from both planes and ground.
I live near Joondalup so I know I'm quite a long way away from the air port and one would expect pretty poor reception from the ground. But why then do some of the frequencies boom in? The only thing I can think of is that there are transmitters located at the airport sight and others that are located maybe in the hills. How close to mark am I?

Thanks all

Sol

all Approach, Departure, Ground, ATIS, Clearance, and Radar frequency transmitters are located at the respective airport... Melbourne Centre Frequencies are assisted by VHF repeaters... placed at certain locations around australia.

the Centre controller in the perth area has multiple frequencies in his controll, all repeated onto eachother. so if you are hearing an aircraft calling centre on the ground somewhere may actually be picked up by a different repeater, and repeated onto the frequency you are listening to.

i will post that image if i can find it.

i used to have a link displaying this, but cannot find it at the moment

Whilst its not my field of expertise I think you are more or less on the right track SOL, the transmitters carrying the tower frequency and ATIS for example are located at the airport up on the control tower. The approach, departure and centre frequencies are transmitted from sites up in Kalamunda and Parkerville and as such the line of sight required for VHF will be better at your location. The outputs from these transmitters up on the hill is also more powerful than that of the ones mounted on the control tower. Someone may be able to better explain it for you but this is my understanding of it all.

Thanks for that, makes it look a bit clearer. I had a feeling that sometimes different frquencies carried the same trafic but it's a bit hard to prove with one scanner. I've bought an icom PCR-1500 recently so I should be able to find any shared frequencies by comparing channels with my old ubc9000xlt. I made up a 1/4 wave ground plane and tuned it up to the centre of the air band and stuck a preamp on it. Reception is reasonable and it's interesting to do a comparison with my scanner ant, both have different reception paterns. All good fun
If any one has any further info on the TX's it would be appreciated.

Thanks again.

As others have said, some of the transmitters for the air band frequencies are located at the airports themselves, but others are off-site, located up in the Darling Range for better coverage.

For example, this is one of the Melbourne Centre frequencies - 133.900MHz:


From the information on that page, we can see that the site in the hills is transmitting an AM voice signal with 6kHz bandwidth at 50 Watts of power on 133.900MHz.

By comparison, the tower frequency for Perth Airport's record shows:


In this image, we can see that the site is the control tower at the airport, the signal is AM voice again with a 6kHz bandwidth, same as the other one, but this time the signal is only at 20 Watts of power on 120.500MHz.

This means the transmissions from the lower are at a lower power level, and the transmitter is located down on the flat land of the plain, rather than up in the hills. Which is why SOL will be having trouble picking up these types of transmissions from Joonadlup...

Hope this helps

By the way ... a couple of links ...

This link lets you search for frequencies and sites as I did, while this link shows what "Melbourne Center" actually looks like

SOL wrote:I've bought an icom PCR-1500 recently so …

Let us know what you think of this receiver once you've had a good play with it. The reviews forum is here http://warsug.info/viewforum.php?f=24

Food for thought Thanks.