Airband atmospheric effects

A place to talk about everything Radio and Scanning

Airband atmospheric effects

Postby andrewgm » Wed Jul 10, 2019 8:37 am

First post

I'm new to the forum but have been scanning Civil Airband frequencies for a few months and have noticed changes in signal strength at certain times of the day which at first thought were down to my receivers under performing.
Anyone else noticed this ?

I can receive my local tower and hear quite clearly what they are saying to the planes coming in and out of the airfield but it's much stronger in the morning.
Once it gets darker it becomes more distant - audible but distant.
Is it me being a bit dim here ?
Are there some changes in how signals travel due to light or the sun for example ?
I'm fairly certain I'm going to get clobbered for not knowing the science behind it but if I don't ask...... haha

Bizarrely last night ( and in total contrast to what I've just said ) I quite clearly heard a pilot transmit on 125.475 that he was over Exeter and even heard a tower reply very clearly.....I'm in Newcastle upon Tyne btw.
My head turned very quickly when I heard it....I don't drink or do drugs either !

I googled the frequency and found it could be a Penrith based tower which is probably 60 miles from me and over mountains.
But Exeter ? Hello ?
My furthest plane receive point has been Leicester and Manchester prior to this using Flightradar24 as a tracker hence my surprise last night.

Apologies for the potentially stupid atmospheric question then and looking forward to using this very interesting site

Andrew
andrewgm
 
Posts: 2
Joined: Sun Jun 09, 2019 12:09 pm

Re: Airband atmospheric effects

Postby Minus1 » Wed Jul 10, 2019 5:12 pm

125.475 is London Information North.
The transmitter you are probably receiving is Great Dun Fell on the hills east of Penrith.
London Info North is sometimes BANDBOXED with London Info West on 125.75 and/or London Info East On 124.6
At quiet times of the day the three frequencies are run by one air traffic controller in Swanwick, and are connected together by landline/microwave link, so what is received on one freq by any of the sites is relayed on the other two frequencies, so that aircraft that are hundreds of miles apart and using different frequencies do not talk over one another.
125.475 is also used at Snaefell and Overstrand (NATS call it 'Trimmingham').
124.75 is used at Clee Hill, Davidstow Moor, and Ventnor.
124.6 is used by Waltham (NATS call it 'Grantham') and probably several other sites.
Multiple sites using the same nominal frequency use transmission frequencies offset by -5kHz/+5kHz or -7.5kHz/0kHz/7.5kHz to reduce interference.

You do get dx on VHF Air occasionally.
Some years ago I got Jersey Approach load and clear (I'm in Birmingham!)
I reserve the right to ignore people who have made no attempt to the read the manual, and expect others to do it for them.
User avatar
Minus1
 
Posts: 947
Joined: Fri Jun 05, 2015 8:17 am
Location: West Midlands

Re: Airband atmospheric effects

Postby andrewgm » Wed Jul 10, 2019 8:04 pm

Minus1 wrote:125.475 is London Information North.
The transmitter you are probably receiving is Great Dun Fell on the hills east of Penrith.
London Info North is sometimes BANDBOXED with London Info West on 125.75 and/or London Info East On 124.6
At quiet times of the day the three frequencies are run by one air traffic controller in Swanwick, and are connected together by landline/microwave link, so what is received on one freq by any of the sites is relayed on the other two frequencies, so that aircraft that are hundreds of miles apart and using different frequencies do not talk over one another.
125.475 is also used at Snaefell and Overstrand (NATS call it 'Trimmingham').
124.75 is used at Clee Hill, Davidstow Moor, and Ventnor.
124.6 is used by Waltham (NATS call it 'Grantham') and probably several other sites.
Multiple sites using the same nominal frequency use transmission frequencies offset by -5kHz/+5kHz or -7.5kHz/0kHz/7.5kHz to reduce interference.

You do get dx on VHF Air occasionally.
Some years ago I got Jersey Approach load and clear (I'm in Birmingham!)


Thank you for this most informative reply Minus1 !
I bet you jumped out of your chair with the Jersey radar signal !

So I've now programmed this frequency into my scanning receiver and all day it's been eye popping - unreal distances of receive !
I'm absolutely delighted with it - much more involving than boring 1 way pilot comms.
I had of course no idea this infrastructure exists in the country so thanks for pointing it out.
It makes perfect sense when you actually see how may planes are in the sky at one time - flightradar was another eye opener for that too.

I fitted a boom at the weekend to my chimney stack so my antenna will be on it in the next few days.
I'm hoping there's another step up in reception and distance once it's all done.
I'm really hooked now !

My wife now thinks I need a psychiatrist.....and she may be right :thumbup: :thumbup: :shocker:
andrewgm
 
Posts: 2
Joined: Sun Jun 09, 2019 12:09 pm

Re: Airband atmospheric effects

Postby Minus1 » Thu Jul 11, 2019 8:54 am

The ATC transmitter at Craigowl near Dundee is not that far away, and line of sight from high ground along the Northumbria coast.
It's receivable from the high ground near St Abbs/Eyemouth, and from Ros Hill near Chillingham if you fancy a little stroll :wink:
124.5 126:930 134.775 234.5 278.55
I reserve the right to ignore people who have made no attempt to the read the manual, and expect others to do it for them.
User avatar
Minus1
 
Posts: 947
Joined: Fri Jun 05, 2015 8:17 am
Location: West Midlands

Re: Airband atmospheric effects

Postby GalaxianFive » Fri Jul 19, 2019 12:16 pm

I too thank you for this info, I found one of these freq by accident and now with the rest the amount of traffic and info is amazing.
GalaxianFive
 
Posts: 22
Joined: Sun Jan 07, 2018 12:09 pm
Location: Taverham

Re: Airband atmospheric effects

Postby G4RMT » Sun Jul 21, 2019 3:30 pm

If you live on the coast then a phenomenon called tropospheric ducting is really fascinating - temperature inversions over the sea create a kind of tunnel - and RF gets into it at one end, and falls out where the duct ends - usually once it gets to land. it means that here in coastal suffolk it's common in the summer months to hear the tower frequencies in Holland, or hear PMR446 users chatting on the dutch beach - radio hams of course will use it, and sometimes it totally destroys our Freeview reception where it romps in from Holland on the same frequencies we use, corrupts the signal and everyone's TV sets go blank!
G4RMT
 
Posts: 1432
Joined: Sat Feb 07, 2015 5:45 pm


Return to Radio and Scanning Chat

Who is online

Users browsing this forum: No registered users and 2 guests