London Control 131.1166

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Re: London Control 131.1166

Postby m0lsx » Tue Mar 01, 2016 4:33 pm

A harmonic is a multiple of the fundamental frequency, that is the wanted frequency, the one in use. So 10mhz, would have harmonics at 20, 30, 40, 50 MHz etc . It is not a multiple of the channel spacings or a multiple or a combination of internal frequencies.
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Re: London Control 131.1166

Postby db13 » Sun Nov 27, 2016 8:44 pm

biggles wrote:Hello to all, this is my first post here despite being an airband listener for 38 years! The frequency is indeed 131.125 but interestingly on my UBC125XLT I can't here a thing 8.33Khz below on 131.1166 but I do pick up the transmissions 8.33 above on 131.1333 albeit reduced signal strength. I guess it all depends on the sensitivity and selectivity of your radio. Ridiculous idea to have 8.33 channels as ATC units tend not to use channels either side if their within VHF range of another sectors frequency. Interestingly I heard an exec jet climbing out of Luton heading north last week to go transatlantic that caused slight problems for ATC as he wasn't 8.33 channel equipped.

Maybe your scanner is a few kHz off frequency.
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Re: London Control 131.1166

Postby db13 » Sun Nov 27, 2016 9:09 pm

Minus1 wrote:
saxonia wrote:Yes I agree I am stuggling to get to grips with this .... 131.125 is Daventry Sector 32 which is what we can apparently hear on the youtube footage. This is also shown in various publications as 131.13.

Now the frequency shown on the Bearcat scanner is 131.1166 which is shown on your link below as 131.115. Now surely you would not hear 131.125 on 131.1166 as you would need to programme 131.125 into the Bearcat to hear this ???

131.115 131.1166
131.130 131.1250


Those publications are using the "frequency" published by NATS and spoken by Air Traffic Control.
Except it is not a precise "frequency", it is effectively a "channel".
If the frequency is 131.125 with a bandwidth of 8 ⅓ kHz, the convention is to call this channel "131.13".
The same frequency with a bandwidth of 25kHz is called "131.125".
Both are the SAME FREQUENCY, only the bandwidth is different.

Yes you WOULD hear it. The scanner has a 25kHz wide AM receiver. It does not have a 8 ⅓ kHz wide AM receiver. If you try and listen to a 8 ⅓ kHz AM transmission on a receiver that is designed for 25 kHz wide AM reception it is entirely likely that you will detect THREE 8 ⅓ kHz channels.
In this case 131.11666666666 131.125 131.13333333333

There are very few scanners that can properly handle 8 ⅓ kHz transmissions.
They may be able to select the frequency, but they do not implement an 8 ⅓ kHz bandwidth AM receiver.

I believe the new AOR DV1 has the facility, as you can select various bandwidths, but I doubt that even implements Eurocontrol's bizarre frequency/channel numbering and thus selects the appropriate filter bandwidth automatically depending on what frequency/channel you key in.
It you want that, you'd best speak to Airbus or Boeing.


No scanner is likely to be as wide as 25kHz when set to AM. 15kHz is more typical.

The actual transmissions are always of similar width no matter which channel system is used. With AM the transmission width is always twice the maximum audio frequency, probably around 7kHz wide for a voice channel.

It used to be that some 25kHz channels were covered by up to three transmitters on the ground, one on exactly on the 25kHz channel and one each 7kHz below and 7kHz above. The receivers in the aircraft, presumably having a bandwidth around 15-20kHz would receive any one of them adequately and a mixture of them wouldn't sound too distorted either since the 7kHz beat frequency is well outside the normal speech range.

I don't know if this is still done or not. Anyone know?

If it is the receivers would need a wide filter for the 25kHz channels and a narrower one for the 8⅓kHz ones.

Also if this is still done it could be one reason why someone would incorrectly identify transmissions from ground station on a 25kHz channel as being on the 8⅓kHz channel below it.
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Re: London Control 131.1166

Postby G4RMT » Mon Nov 28, 2016 8:37 am

There's only a year to go now before even the light aircraft MUST have 8.3KHz equipped radios - so queries like this will be getting more and more common I guess. I suppose getting a world wide standard acceptable to everyone must have been tricky. Can we assume some countries said we want 12.5KHz, others said 6.25KHz, and they just averaged it out to a new, daft one?
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Re: London Control 131.1166

Postby Minus1 » Tue Nov 29, 2016 7:12 pm

db13 wrote:It used to be that some 25kHz channels were covered by up to three transmitters on the ground, one on exactly on the 25kHz channel and one each 7kHz below and 7kHz above. The receivers in the aircraft, presumably having a bandwidth around 15-20kHz would receive any one of them adequately and a mixture of them wouldn't sound too distorted either since the 7kHz beat frequency is well outside the normal speech range.

I don't know if this is still done or not. Anyone know?



Yes, check the Volmet transmissions (if you are near a transmitter that doesn't use the centre freq of course)

The "128.6" Volmet transmisson from Clee Hill is actually on 128.5925 (so uses -7.5 kHz)
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Re: London Control 131.1166

Postby Minus1 » Wed Nov 30, 2016 9:32 am

G4RMT wrote:There's only a year to go now before even the light aircraft MUST have 8.3KHz equipped radios - so queries like this will be getting more and more common I guess. I suppose getting a world wide standard acceptable to everyone must have been tricky. Can we assume some countries said we want 12.5KHz, others said 6.25KHz, and they just averaged it out to a new, daft one?


They should have gone to 10kHz. Most sensible option, the technology is clearly practical, and we could have avoided the nonsense of "frequencies" that are not frequencies. Typical of the EU to mess things up. :rolleyes:
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Re: London Control 131.1166

Postby db13 » Sun Jan 01, 2017 2:51 am

Minus1 wrote:
G4RMT wrote:There's only a year to go now before even the light aircraft MUST have 8.3KHz equipped radios - so queries like this will be getting more and more common I guess. I suppose getting a world wide standard acceptable to everyone must have been tricky. Can we assume some countries said we want 12.5KHz, others said 6.25KHz, and they just averaged it out to a new, daft one?


They should have gone to 10kHz. Most sensible option, the technology is clearly practical, and we could have avoided the nonsense of "frequencies" that are not frequencies. Typical of the EU to mess things up. :rolleyes:


They would still need some easy way of differentiating between 128.600 the wide 25kHz channel that may use several transmitters spaced 7.5kHz above, below and exactly on channel and the new narrow 128.600 channel.

Plus half the old 25kHz channels would not be tunable on new 10Khz spaced equipment without a kludge.
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