R/T Break through
Warning Toxic!
Disgusted of Tunbridge
Disgusted of Tunbridge
Joined: Jan 2005
Posts: 4,011
Likes: 1
From: Hampshire, UK
Sudden short duration bursts of transmission coming through on the radio. Usually associated with high pressure air causing funneling of transmissions from a long way away. You would not hear on the ground.
Joined: May 2004
Posts: 218
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From: Granada, Spain
If there is a local VHF FM station on 97.3MHz this could cause problems to some radios having a Local Oscillator Frequency 0f 10.7MHz. If memory serves its called Second Channel interference...97.3Mhz might just be a local commercial station...
As I recall Rockwell -Collins VHF-20's were particularly susceptible to this problem and is the principle reason why FM Immunity mods were introduced to some VHF Nav receivers...
As I recall Rockwell -Collins VHF-20's were particularly susceptible to this problem and is the principle reason why FM Immunity mods were introduced to some VHF Nav receivers...
Joined: May 2000
Posts: 1,021
Likes: 2
From: Glorious West Sussex
Rainboe
Nah, mate, that is "Duct Propagation" on the same frequency.
Breakthrough is an irritation from an adjacent frequency.
Sudden short duration bursts of transmission coming through on the radio. Usually associated with high pressure air causing funneling of transmissions from a long way away.
Breakthrough is an irritation from an adjacent frequency.
Joined: Jun 2001
Posts: 3,991
Likes: 8
From: UK
Indeed it is, and can travel rather long distances.
Sudden short duration bursts of transmission coming through on the radio. Usually associated with high pressure air causing funneling of transmissions from a long way away.
Radio Hams like this though so they can get extra long range on VHF!
Joined: Jan 2007
Posts: 99
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From: Between EGAA, EGAC & the wilds of England
If there is a local VHF FM station on 97.3MHz this could cause problems to some radios having a Local Oscillator Frequency 0f 10.7MHz. If memory serves its called Second Channel interference...97.3Mhz might just be a local commercial station...
Joined: Jun 2009
Posts: 1,330
Likes: 0
From: NNW of Antipodes
If there is a local VHF FM station on 97.3MHz this could cause problems to some radios having a Local Oscillator Frequency 0f 10.7MHz. If memory serves its called Second Channel interference...97.3Mhz might just be a local commercial station...
So, what you are really talking about is Image Frequency interference which can enter the receiver if there is insufficient front end filtering, i.e. poor rejection of out of band signals. The interfering signals will be at +/- twice the IF frequency from 118.7MHz, i.e. 97.3MHz or 140.1MHz. 97.3MHz has already been identified as the FM broadcast station LBC transmitting from Croydon.
Any decent Aeronautical VHF receiver will have high attenuation notch filters centered on the 88 ~ 108 FM broadcast band, and problems from that band should be extremely minimal.
The answer to the "breakthrough" question is that it is most likely tropospheric ducting caused by temperature inversions in the troposphere which can happen when a large high pressure system has been hanging around for a while. In this case the transmission breakthrough probably came from an aircraft using the same frequency with an ATC somewhere in Europe, e.g. Orly Approach.
An ICAO paper has been written on this subject and can be found at - http://www.icao.int/anb/panels/acp/w...0/wgd10_07.pdf
mm43
