Radio Quality and Transmission Quality

[DeltaoneZero]

I live in the Northwest area of the UK, and it has come to my attention recently over the Radio Quality and Transmission Quality of some broadcasts being made by aircraft (and possibly stations) and I was wondering about your comments.

What I have noticed is how the quality of some G.A aircraft broadcasts; have in my view, deteriated and nothing appears to be getting done about them? I Regularly listen to the VHF frequencies of ATSU's in my area, and I have noticed over a period of time there are regular offenders that are very hard to understand, and one can only assume if I am having problems understanding transmissions then how do the people for who it matters understand? - E.g. other fellow Pilots, ATC etc etc

I am sure that a.c are reminded of there radio quality on initial 'call up' - but what I can not understand is that if this is the case, then why is nothing being done about it?
I am aware that not every aircraft can be perfect, and I know some of older aircraft can suffer with problems in having newer av kits installed, but it does make me wonder how come a 1950's Chipmunk can have a better quality/sounding radio than a 80' Cessna 150 (for example).

Also, something else for you to consider before you write your replies. Should the old standard scale of 1-5 be used anymore? If so should it not be made more accurate - after all what is clear and precise to one person, may not be to another?

As always, looking forward to your views;
:):confused:

[FWA NATCA]

This problem is not unique to the UK, we have the same problem here in the US, and it isn't just aircraft, some of our air traffic facilities have problems with their transcivers and or ICSS equipment too.

Mike

[bagpuss lives]

Having once jumpseated over Africa I think the clarity of even the poorest quality transmissions in this country are perfect in comparison.

With regard to the transmissions by stations I presume you are aware of the slight off-setting of frequency for most ATC ground transmitters? If not (please don't let me teach you to suck eggs on this one) then tuning approx 5kHz either side of a ground station will improve quality no end. Of course if you do that aeronautical mobile stations will sound even more off frequency.

What you tend to find too is that after using radio in its many forms for a considerable period of time one acquires "RT Hearing" in that even the most unintelligible transmission gets decoded into something useful somewhere in the deep grey matter.

Much is to do with the quality of the microphone too of course - both in the air in your typical Cessna and on the ground. When LACC opened there were countless problems with clarity and volume of transmissions all of which were traced to the headset equipment.

[Findo]

In general there is nothing wrong with the quality of aircraft transmitters. Any which are faulty are pretty quickly put right. The standard procedure would be to ask the pilot to use another box.

I suspect the problem may lie with your receiver. ;) ;)

[mad_jock]

He is proberly trying to listen to the advisory Route from INV to Lewis.

Don't worry most of the planes can't hear scottish either :D

And when you do get them during JMC its your in the middle of high energy manovers "Good luck"

MJ

[DeltaoneZero]

Howdy all, Sorry i should of been more precise, I meant the Northwest of England (merseyside etc) and not as far as scotland.

As Regards to my ''Reciever'' it works very well, i pick 99% of the aircraft up Ok, just the odd few! - the same ones are always bad

Hope you had a good Christmas :)

[turn right heading 365]

I agree with you Deltaone that there are some cr*p radios out there, and as has been mentioned you do get accustomed to being able to decipher it. Some pilots with bad radios are better at getting their message across than some pilots with 5x5 transmission quality but who tell you everything except what you really need to know, but I digress...

I think the 1-5 readability scale is good as it saves people describing your transmission with a lot of words whereas the scale is at least concise. It is subjective though. After years of listening to HF in a remote corner of the globe, where there the best readability you gave anyone was 4, VHF even at its worst would probably get no less than a 3 from me, but maybe 1 from someone else.

As far as what can be done about it, well you give pilots a radio check and unless it is totally unreadable you are hardly going to send them back to the apron and spoil their day (talking about club flying here). Maybe we should phone the club/school concerned but I for one usually forget!!

[FlyingForFun]

Niteflite,With regard to the transmissions by stations I presume you are aware of the slight off-setting of frequency for most ATC ground transmitters?For those of us who are not aware of this, would you care to enlighten us? (More details, reasons, etc?)

Thanks!

FFF
-------------

[bagpuss lives]

Cor blimey I'm trawling my memory here but I'll try :D

Most ACC frequencies are transmitted from more than one Tx location. For instance at Manchester for one of the sectors we have transmitters in both Lancashire and deepest darkest Cheshire (exact locations withheld for obvious reasons).

If both of those transmitters were on precisely the same frequency any airborne station would just hear the horrible squealing cross-modulation of two stations transmitting at once.

To counter-act this each transmitter is adjusted so it's slightly off-frequency and thus each of them aren't transmitting over each other. So therefore the Cheshire Tx maybe be transmitting on 134.420Mhz and the Lancashire one 134.430MHz.

This slight off-setting tolerance is in-built into airborne radio equipment but anyone listening with a scanner who is closer to one of the stations would think that it was trnasmitting slightly off-frequency. Maybe then they'd need to alter the frequency they were tuned to by about 5kHz.

Someone could probably explain better than I have as it's been a looooong time since I had to learn all of this :D

Hope this helps anyway :)

[FlyingForFun]

Ah - never heard of that before, but it makes sense the way you describe it! Presumably only applies to larger stations, though? I can't imagine that, for example, Waltham Radio (chosen only because it's my home airfield) would have any need for two separate transmitters?

FFF
---------------

[bagpuss lives]

Yeah I think it only operates at large transmitter sites as you say. Sites where another location may also be transmitting the same frequencies :)

Glad it made sense to you - it didn't to me as I was typing it :D

[slim_slag]

niteflite01,

How does this affect 8.33kHz spacing?

[forget]

How does this affect 8.33kHz spacing? Off Set Carrier cannot be used with 8.33.

[bagpuss lives]

I don't know how it works over the Channel to be honest as we don't have 8.33kHz spacing in the UK yet as you know. I suppose though that the same aircraft use the UK 25kHz spaced frequencies that use the 8.33kHz spaced ones so I would presume that the tolerance on the new 8.33kHz airborne equipment has been made much much smaller. Either that or offsetting is not used - which is a distinct possibility.

If I can dig out my original documentation on the subject later on I will do so and post a more enlightened comment but my short answer is : I don't know :)

[Simtech]

From memory, in the UK the frequency offset is 7.5 kHz. So, if three transmitters are required to give the required geographical coverage, one will be on the nominal frequency, one will be 7.5 kHz above nominal and the other 7.5 kHz below nominal. When the transmitters are keyed an audio howl (hetrodyne) will be produced, caused by simultaneous transmission on different frequencies. This is often heard when two aircraft transmit simultaneously on the same frequency. However, with frequency offset transmitters the howl is not heard by the aircraft as the frequencies produced (in this case 7.5 kHz and 15 kHz) are above the upper limit of the receiver's audio passband (normally about 2.7 kHz) and are thus filtered out.

[forget]

8.33 cannot use Off-Set Carrier. See Eurocontrol's user guide.

http://www.mfom.es/aviacioncivil/pr...r_guide_5_1.pdf

[vintage ATCO]

Simtech

I think you'll find the offset is +/- 5KHz, at least ours are.


forget

That link doesn't seem to work. Interesting they'll be no offset with 8.33. I wonder what they'll do? :confused:


VA

[Simtech]

VA ,

Thanks for the correction. I'd forgotten that EGGW uses multiple transmit sites. I'm there at the moment, counting the hours until my shift finishes.

Cheers,

Simtech

[forget]

Sorry about the duff link, it’s

http://www.eurocontrol.int/vhf833/Documents/User_Guide/8.33khz_user_guide_english.pdf


Para 3.1.1.

Aircraft VHF radio equipment in the ICAO EUR Region will still be required to be able to tune to 25 kHz spaced channels and receive in an environment which uses offset-carrier systems (the so-called CLIMAX operation). Airspace users should take into account that these offset-carrier systems will continue to be used throughout Europe.

[DeltaoneZero]

Hello All, Thanks for the replies and I hope your enjoying your new year!

Ok, I am pleased with the response that you have all given including the technical details provided by niteflite01 (I am sure we have met before? :confused: ) - Just goes to show after many years of doing the job you can still remember the knowledge!

The receiver i have used is of a good make, and I am sure its nothing todo with it being set incorrectly as after taking your advice i recently tuned into a local ATSU Providing FIS to hear the same aircraft that a normally hear having the same distorted radio quality! It appears, or should that be sounds to me, that the radio or headsets are ''over modulating'' the radio transmission

Anyway thanks for your comments and look forward to any more replies :)

Edited to remove identity of aircraft

[Lon More]

we used 833 apacing at Maastricht since the start; previously no real problems but now a lot. Often the same a/c will occasionally be 5X5; then 5 min later 1x1 for some reason; coverage seems to be patchy. Ongoing investigation

[zed3]

Going a bit off tack here .....but anyone remember (aaah) the old BOAC VC10s - lovely sound , nice crisp r/t with no background noise , can still hear them calling over DVR now!!! Which boxes were they then ? anyone know ?

[bagpuss lives]

Also straying a little bit off track but I'd like to nominate BAL and AMM (FCA now) for the "R/T Clarity Award 2003" :D They're also mightily crisp and clear.

Delta One Zero - I don't *think* we've met before - certainly not on these hallowed pages anyhow? Maybe you've had the privilege in the past of corresponding with someone who shared my poor knowledge in a wide range of useless topics? :D

That'll be it :ok:

[Squadgy]

I know the operators of the cessna you have in mind have been working on this problem, at present trying out some different headsets - it this dosen't work then I understand they will be looking to have the radio bench tested.
Hope this is the response you were looking for. :hmm:

[PPRuNe Radar]

DeltaoneZero

It is not clear if you are using an ATSU facility, an aircraft radio, or a 'scanner' or some other device. If the latter then what you are doing is technically illegal. There are a few threads on the site which point to the relevant legislation.

Assuming you are operating legally and listening in a licenced capacity, then it is most certainly illegal to make use of any information that you come across which does not directly concern you so please don't create potential problems for this site by giving examples and naming and shaming operators (not too many aircraft in your neck of the woods with the type and registration which you gave, and this has now been deleted.)

Of course, if you are complaining about the quality of an aircrafts radio from an ATSU point of view, then there are ways and means to do that officially. Many on here can give you advice on how to go about that if you are unsure. PPRuNe is not one of the methods. If it's a complaint from a 'scanning' point of view, then sorry but that's not really of much concern to ATC nor pilots alike to be honest. The aviation RT band exists for the benefit of legitimate users, not as a form of entertainment or to allow gossip to spread. Controllers at ATSUs are the best judges of whether RT quality is adequate and can ensure that poor quality radios are identified to the aircraft operators swiftly.

[bagpuss lives]

Perhaps you should also remove some of the technical information I posted - just to be on the safe side.

With hindsight I see your point Radar and agree totally.

[PPRuNe Radar]

Niteflight01

Everything you have mentioned technically is in the public domain and generic enough to remain in PPRuNe's view.

It is no different from other kinds of posts on the site which discuss technical procedures, etc, employed by airlines or specific to aircraft types. All of which serve to educate the readers and increase understanding.

The issue here was more one of an individual aircraft being identified and that potentially creating problems for the operator if those in authority identified it, as well as creating a reputation for the aircraft amongst ATC circles perhaps. As stated, if ATSUs formally have a problem with a specific aircraft then it can be dealt with by them and not on PPRuNe.

It was also not clear in which capacity, and technically how, the information was gleaned.

Whilst I have never heard of a case of anyone being charged for using information gained from the non public radio bands, we wouldn't like PPRuNe to be involved in any test cases :ok: :O

[Please note that there is no allegation that the thread starter has necessarily done anything illegal, just that there is not enough information to stop all the alarm bells going off at PPRuNe HQ. We assume the worst case and thus our duty remains to protect the site.]

[DeltaoneZero]

PPRUNE RADAR,

Just to clear a few things up. My Method of listening to the Transmissions is legal. I Have not clearly defined how i ''listen in'' as I wish to remain anonymous on here. I Take your views into consideration and will act upon them when next making a post.


However a few other points/questions i have.

How come in the USA they can broadcast R/T over a source like the Internet etc? However in the UK we cant legally listen or use these frequencies with out holding a R/T Licence?
Also if it is illegal to use a Scanner to listen to a R/T Frequency (like most spotters will use - say at EGCC or EGGP) then how come they are readily available? And don’t carry a clear warning?

Just a few thoughts..

Happy Posting and a Very Happy New Year! :)

[bagpuss lives]

I'll answer some of that if I can in lieu of Radar....

Basically in the UK we have the Wireless and Telegraphy Act of 1949 that governs what we may and may not listen to legally. We also have a few other laws like the Interception of Communications Act and now even the new Prevention of Terrorism Act (revised) which also dictate what we can and can't do with regard to this matter.

I'm sure you know the finer points of the law.....

Reception and rebroadcasting of any "scanner" audio is strictly illegal and, depending on what it is you're rebroadcasting, you could find a pair of Size 10 standard issue boots and the odd flash-bang through your door for doing it. Rightly so if you're rebroadcasting something naughty.

In the US, generally speaking, the laws that govern radio are slightly less stringent. Whilst in the UK scanner users are not permitted to listen to almost anything, over the pond it's illegal to monitor phones, encrypted systems, use a radio as an aid to crime and use any information heard for personal gain and that's about it. Anything else goes and note, no mention of the "airband".

Thusly in most US states listening to airband traffic is, as I interpret it, loosely legal. Therefore there's nothing to stop joe public rebroadcasting the audio as they wish. Indeed, as far as I'm aware, Airband transmissions are classified as "readily available to the public" anyhow.

This all may have changed, rightfully so in my opinion, in light of recent World events.

As for the "why is the equipment readily available" question - it's simple.

A car is illegal if used in certain ways. That doesn't make buying or using the actual vehicle illegal.

So therefore your average scanning receiver I would imagine (not being any sort of an expert in the matter you understand) is capable of monitoring lots of very LEGAL transmissions (licenced amateurs, commercial stations, CB that sort of thing).

Ignorance of the law is no defence in this case.

In the UK the law enforcement agencies have, in the past, turned a massive "blind eye" to airband listening, especially in the vicinity of airports. Most officers use their discretion and view it as a harmless past time.

These days however, you really can't be too careful in more ways than one. So I wouldn't be surprised to see them clamp down a little in the future.

I think it'll only be a matter of time before our laws are changed in some way to reflect the sorry state the world is in and that not everyone within it can be trusted to be sensible.

I'd like to add, for those that read here and aren't aware, that the Wireless and Telegraphy Act 1949 does not permit monitoring aeronautical fixed or mobile stations unless you hold proper authority or a licence to do so. In other words if you do listen to ATC comms, keep it to yourself and be aware that you are breaking the law, technically speaking.

[PPRuNe Radar]

Thanks DeltaoneZero

Happy New Year to you as well :ok:

The following from the Radiocommunications Agency may help explain the UK position.

Receive-Only Radio Scanners etc.

The purpose of this information sheet is to remove any confusion regarding the reception of personal or business radio transmissions by unauthorised persons or groups. It also gives guidance on the subject by setting out the legal position with regard to the Wireless Telegraphy Act 1949 (WT Act). How the legislation is applied will depend on the individual circumstances of the offence.

Anyone who intends to listen to radio transmissions should be aware of the following:

A licence is not required for a radio receiver as long as it is not capable of transmission as well (The Wireless Telegraphy Apparatus (Receivers) (Exemption) Regulations 1989 (SI 1989 No 123). The exception to this is that it is an offence to listen to unlicensed broadcasters (pirates) without a licence. Licences are not issued for this purpose.

Although it is not illegal to sell, buy or own a scanning or other receiver in the UK, it must only be used to listen to transmissions meant for GENERAL RECEPTION. The services that you can listen to include Amateur and Citizens' Band transmissions, licensed broadcast radio and weather and navigation broadcasts.

It is an offence to listen to any other radio services unless you are authorised by a designated person to do so.

There are two offences under law:

Under Section 5(1)(b) of the WT Act 1949 it is an offence if a person "otherwise than under the authority of a designated person,

either:

(i) uses any wireless telegraphy apparatus with intent to obtain information as to the contents, sender or addressee of any message whether sent by means of wireless telegraphy or not, of which neither the person using the apparatus nor a person on whose behalf he is acting is an intended recipient;

This means that it is illegal to listen to anything other than general reception transmissions unless you are either a licensed user of the frequencies in question or have been specifically authorised to do so by a designated person. A designated person means:

the Secretary of State;

the Commissioners of Customs and Excise; or

any other person designated for the purpose by regulations made by the Secretary of State.

or:

(ii) except in the course of legal proceedings or for the purpose of any report thereof, discloses any information as to the contents, sender or addressee of any such message, being information which would not have come to his knowledge but for the use of wireless telegraphy apparatus by him or by another person."

This means that it is also illegal to tell a third party what you have heard.

With certain exceptions, it is an offence under Section 1 of the Regulation of Investigatory Powers Act 2000 for a person -

"intentionally and without lawful authority to intercept, at any place in the United Kingdom, any communication in the course of its transmission by means of: a public postal service; or a public telecommunication system."

It is similarly an offence to intercept any communication in the course of its transmission by means of a private telecommunication system.

This means that it is illegal to listen to telephone calls, including mobile phone networks which are designated as forming part of the public telecommunications system.

Common questions answered

Q. Am I breaking the law by owning a scanner?

A. No, but it is illegal to use one to listen to frequencies other than general reception transmissions or those parts of the radio spectrum which your transmitting licence, if you have one, allows you to use. You could be prosecuted for this.

Q. Can I get a licence to use a scanner?

A. No, there is no scanner licence.

Q. Could I get authority to listen to emergency service transmissions, for example? I am interested and might be able to help.

A. No, authority is reserved for people acting under statutory authority. If you wish to listen in to messages, you should obtain the permission of the person sending them.

Q. Isn't it all right to listen as long as I don't pass on what I hear?

A. No, using radio equipment to listen in, except as provided by section 5(1)(b) of the WT Act, is an offence, regardless of whether the information is passed on.

Q. Isn't this all a bit heavy?

A. No. No-one likes their private or business conversations to be listened to. Parliament has passed these laws to protect the privacy of radio users.

If you require more information on the law regarding receive-only radio and scanners, please write to:

RA3/Enforcement Policy Unit,
Radiocommunications Agency
Wyndham House
189 Marsh Wall
London
E14 9SX

For further information on other radio matters contact the Agency's 24 hr
Enquiry Point on 020 7211 0211

or e-mail on [email protected]

RA 169 (REV 7)
January 2001