Airband radio question

[fonawah]

Moderator if this is on the wrong forum, please redirect.

I have a question about airband radios. I recently bought one and I was wondering about the transmissions. I seem to be able to hear the pilots` transmissions to tower, or Manchester control. I cannot hear the transmissions from tower to aircraft or from say Manchester Control to the aircraft. Is that something to do with my location or should my radio be able to pick up both transmissions if it can pick up the transmission from aircraft to tower or control?
I hope I have not made this a confusing question !!
Many thanks for any help.
F :D

[HZ123]

I am sure that someone will respond with actuals but I believe that out / in transmissions are on different wavelengths which is why you hear one but not the other.

[Tony Flynn]

Years ago when I lived in North Wales I found the same thing to be true. I now live in Lightwater in Surrey and can hear both ends of the conversation clearly. It's always going to be easy to hear aircraft, radio waves travel generally in straight lines, an aircraft a couple of thousand feet up has an unhindered radio path to your receiver but the tower transmissions are most probably blocked by terrain between you and the transmitter. Sell up and move to higher ground!

[fonawah]

Cheers Tony,
I thought that might have been the case.

[spekesoftly]

I cannot hear the transmissions ................... from say Manchester Control to the aircraft.

Also bear in mind that the ATC Transmitter Aerials may be located some considerable distance from the ATC facility. This applies to some (all?) of the "Manchester Area Control" frequencies. To receive 'ground to air' ATC transmissions, from ground level, you need to be 'listening' from a position reasonably close to the Tx aerials, not necessarily close to Manchester Airport.

[Dufwer]

HZ123, I don't think you are correct on this one. If the tower and aircraft transmitted on different frequencies while listening to the other's frequency, you would have a situation where aircraft wouldn't be able to hear each other. The aircraft would then not be able to tell if they are talking over each other. I do know of setup at an airfield where only one side of a conversion can be heard on a particular frequency. At Bournemouth communications to ground vehicles can be heard on the tower frequency but the response from the ground vehicles can not be heard. I suspect this is to keep aircraft informed of ground movements, i.e. when vehicles are given permission to the cross the active runway, while the response from the vehicle is of no concern to the aircraft. More likely than not the tower is broadcasting on more than one frequency, i.e. the tower frequency and another the ground vehicles can hear, and is listening out on both.

Back to the original question, VHF communications is line-of-sight. There is a little bit of propagation (refraction or diffraction, can't remember which) that allows it to curve around buildings and over hills, but not much. If you are not near the airfield or the ground based aerial then you won't hear the transmissions.

Regards
D

[FlyingForFun]

I do know of setup at an airfield where only one side of a conversion can be heard on a particular frequencyDoesn't that happen quite often, when a controller is working more than one frequency? Rather than select the frequency for each transmission, the controller simply transmits on all the frequencies he is working, so you get to hear his side of a conversation which isn't for you. At least I think that's what's happening - can anyone confirm? I don't know Bournemouth, but this could explain why you can hear the controller talking to ground vehicles, but not their replies, if they are both listening to and replying on a different frequency to you, and the transmissions are being made on both your frequency and their frequency?

I agree with other replies, though - the most likely reason you can't hear the controllers is because you are not within range of their transmitter. Being on the ground yourself, your line-of-sight range will be much lower than the aircraft they are transmitting to.

As for transmitting on one frequency and receiving on another, the only things I can think of that do this are SSR, and DME (which is a form of SSR) - nothing that would carry a voice signal. Have I missed any?

FFF
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[PaperTiger]

Rather than select the frequency for each transmission, the controller simply transmits on all the frequencies he is working, so you get to hear his side of a conversation which isn't for you. At least I think that's what's happening - can anyone confirm? Yes it's quite common at smaller airports, usually where there are 'outer' and 'inner' tower frequencies.

In addition to the line-of-sight chracteristic of transmissions, the weather also affects hearing ground-to-air calls. Some days they are clear as a bell, other days they are completely inaudible. Sumfing to do wiv sunspots i fink :confused:

[woderick]

Correct FFF. The ground vehicles will be using UHF radio not VHF as Aircraft do. At EGCC their audio is patched through so that both the Aircraft and ground vehicles can hear each other (at least on 'ground')
Airband communication is always SCS (single channel simplex) in my experience. Although a long time ago - the seventies - two aircraft of my acquaintance had an ancient Collins valve Tx/Rx setup that was switchable to Double Channel Simplex ie. transmit and receive on different frequencies, I think we had to modify it out ! The aircraft were ex Aerolinas Argentinas.
Under non atmospherically enhanced conditions a rule of thumb for the extension of line of sight for VHF is 1.23 * Line of Sight distance if memory serves.

[lunkenheimer]

Fonahwah, you might try raising the aerial if you can't move closer. A meter or two of height increase might do the trick.

[fonawah]

Thank you all for your replies.

[rustybh]

If you want to work out the Effective Radio Horizon for V/UHF comms use the following:

(1.23 * sqroot H1) + (1.23 * sqroot H2)

Where H1 is aircraft Height (ft)
Where H2 is ground station height (ft)

It's sad how these things tick in my mind but I could not tell you waht I had for lunch yesterday :uhoh:

[Northern Highflyer]

FFF

When working the Fenton MATZ you can often hear the controllers talking to Military traffic on the UHF but not hear the response so you are right, they do tx on both bands simultaneously.

Fonawah

You can often buy an aeriel to put in your loft which may help you pick up ground tx if you are high enough.

[martinlynch]

It’s also worth checking the squelch setting on your radio.

The tower transmissions will obviously be weaker depending on your proximity, elevation, terrain etc possibly causing them to be “squelched out”.

Apologies if you already know this, but I note that you said you recently bought the radio. If you haven’t already tried, it’s worth opening up the squelch completely to see if you can hear the tower/control transmissions (of course you’ll now get all the background hiss between calls).

[fonawah]

Thanks Martin,
will give that a try