Clipped messages

[ChasG]

In order to help familiarise myself with radio transmissions I bought myself a scanner. While I can audibly hear the transmissions I find it very difficult to understand what is being said. I pick up most of it but miss bits particularly when there is a none BBC type accent. Also lots of the messages seem to be clipped at the end.
I know I find it difficult sometimes to make out what is being said when there is background noise but dont seem to have a problem with the headset when I am listening/talking to the instructor.
I am hoping that the problems is unfamiliarity with RT - I would welcome other peoples experiences

[172driver]

Have you considered listening in to Live ATC (http://www.liveatc.net/feedindex.php) ?

You won't hear a lot of BBC English on there, but it's the real world !

[ChasG]

Thank you for your suggestion - I will have a go

[172driver]

One more thing - you don't really say why you want to become familiar with radio, I assume it's because you are learning to fly. Depending where you are in your training, a lot of r/t may well sound weird at first, as you don't know (yet) what it relates to. It'll all fall into place later on :ok:

[Whiskey Kilo Wanderer]

Hi Chas,

Aeronautical radio is probably the worst technical quality transmission in existence. Apart from being generated in the noisy environment of an aircraft cockpit, it uses AM. This is one of the most interference prone transmission medium in use at the moment.

The only way the system works is that everyone tries to use the standard phraseology, as per CAP 413 (http://www.caa.co.uk/docs/33/CAP413.PDF). That way the people listening to the transmission know what is coming next.

Apart from the poor technical quality there is also the jargon. Some of this dates back to the time when Morse was the only communication method. Things like QNH for altimeter pressure setting etc.

After a while you will find that you get used to the poor quality and the jargon. A common problem for pilots is the fear of messing up on the radio. If you listen on the frequencies of some of the larger airports you will find that everyone has off days on the radio. No one worries too much as long as the message gets through.

If you have a lot of spare time, you might like to look at the ATC Humor Thread (http://www.pprune.org/atc-issues/59309-atc-humour-merged.html). It's mostly about RT transmissions that went wrong.

Safe Flying,
Richard W.

[dublinpilot]

If your radio has a headphone jack, try plugging in your headset. The speakers in your headset are likely to be better than your radio speaker, and it will help to block our background noise.

Also, are you sure that you are hearing both sides of the conversation? If you're not near the airport then you might only be hearing the pilots and only hearing one side of the conversation makes things very difficult to comprehend!

I never found online ATC to be very clear by the way. They are often monitoring multiple frequencies which is very confusing to say the least!

[Whopity]

it uses AM. This is one of the most interference prone transmission medium in use at the moment.Yes it is suscetible to amplitude based interference such as ignition noise and vacumn cleaners but how often do you hear those? AM especially at VHF, where you avoid most of the propagation problems that cause interference, is quite capable of providing good quality audio. Heterodyne interference is probably the only one that blocks reception but is largely eliminated by good operating practice. I totally agree that most light aircraft radio installations are of very poor quality but it is mainly associated with poor engineering and nothing to do with the mode of transmission. In most cases the culprit is poor matching causing boxes to overload and go into distortion. Then add in incorrectly set Squelch levels.

The secret of listening to RT is to know the contents of the various messages so that you only have to fill in the bits of variable information.

[leader12uk]

Hi, I also listen to a lot ATC chatter (mainly Denham and Elstree)and had exactly the same problem although it is obvious the the controller and pilot do not (most of the time anyway) to get around the problem i bought a decent radio AND aerial. The main reason for listening is that i intend take the exam sometime this year and to get back into aviation. (after learning to glide and then start my PPL at Elstree in the 70/80's and then found out i couldnt afford it, now i can afford it, ill health precludes me from taking it up again)

[BackPacker]

If you bought a scanner then there's a cheap and easy way of upgrading its reception capability - build or get a better antenna. The dinky whip antenna that's standard is rubbish since it's got to be very portable and needs to tune to a very large range of frequencies.

You can create a very simple dipole antenna which works magic with some pieces of household electricity wire, a simple connector and a length of RG-58 coaxial cable. This last is maybe the hardest to get. It was used (a decade or so ago) for "thin ethernet" so a computer shop or expert with a sense of nostalgia might have miles of the stuff lying around. Let me know if you need a detailed description.

On the other hand there are a lot of sites on the internet that give access to ATC from around the world, in good quality, so you might not want to bother.

[Jan Olieslagers]

I agree with the suggestion of constructing one's own antenna, for non-mobile. But dipoles are less than optimal due to their directiveness. Better, and not more complicated, to concoct a simple ground-plane antenna (plane NOT meaning aeroplane in this context)

I did this, with help from Circuits Online - Forum - Simpele antenne voor VHF-ontvangst (http://www.circuitsonline.net/forum/view/85521) for those who can make out Dutch language - no prob for BackPacker, I should reckon... Reception improved drastically. One day I'll have to make a better mechanical construction and attach the whole thing in open air, on the roof if possible.

Addition: our alther friend wikipedia pointed me to this nice calculator: Amateur Quarter Wave Ground Plane Antenna Calculator (http://www.csgnetwork.com/antennagpcalc.html)

[Miroku]

Leader12UK

Have you looked at the NPPL? The medical requirements are a lot less onerous than the JAR PPL.

[leader12uk]

Hi,

yes i have. I have very high lood pressure most likely bought on by being overweight!!!. If my diet works and the BP goes down i will probaly reconsider.

[ChasG]

Dear All, thank you yet again for all your responses. I will have a look in the CAP 413 so that I recognise the format. Having looked at your suggestions I think it is most likely to be a combination of issues. I listened to a lady from Northolt which I assume was a recorded message and got most of what she said because the transmission was very clear and she spoke nice and slowly.
I am doing my NPPl at Denham and was a bit concerned that there might be an issue - obviously dont want to spend loads of money only to find out I can not pass the RT

[ChasG]

Just had a look at CAP413 and I am now not suprised I couldnt understand the pronunciation. Apologies I should have checked before posting regards Chas

[stevelup]

I am doing my NPPl at Denham and was a bit concerned that there might be an issue - obviously dont want to spend loads of money only to find out I can not pass the RT

Don't worry about it - at the moment, it's meaningless gobbledegook. Once you know what you are listening out for, it all begins to make sense. Your ears become tuned to it!

If ever you are having any difficulty understanding someone, you can always just say 'Say Again'

[liam548]

Have you considered listening in to Live ATC (http://www.liveatc.net/feedindex.php) ?

You won't hear a lot of BBC English on there, but it's the real world !


Theres also GlobalTuners

[HEATHROW DIRECTOR]

<<I agree with the suggestion of constructing one's own antenna, for non-mobile. But dipoles are less than optimal due to their directiveness.>>

So you hang it up as a vertical dipole, with the wire connected to the braid of the co-ax pointing downwards. That way it becomes omni-directional.

Be forewarned - a lot of cheapo scanners will become overloaded with a more efficient antenna. It won't damage the set, but you may well hear transmissionns which you are not tuned to. Eg a taxi driving past, or the local CB or amateur transmitters may blast through well away from their transmit frequencies.

Lastly, remind yourself of the WT Act: See the sticky on the ATC forum.

[Jan Olieslagers]

<<I agree with the suggestion of constructing one's own antenna, for non-mobile. But dipoles are less than optimal due to their directiveness.>>
So you hang it up as a vertical dipole, with the wire connected to the braid of the co-ax pointing downwards. That way it becomes omni-directional.
That sounds suspiciously like a clever disguise of the ground-plane antenna I recommended - but I am not an expert on antennae.

Be forewarned - a lot of cheapo scanners will become overloaded with a more efficient antenna. It won't damage the set, but you may well hear transmissions which you are not tuned to. Eg a taxi driving past, or the local CB or amateur transmitters may blast through well away from their transmit frequencies.
It was never a problem to me - neither on the Maycom AR108 (how's that for cheapo?) nor on the Icom A6. Perhaps an indication my ground-plane concoction is far from perfection? Or then, in this rural village taxi's are most rare, and CB won't perhaps be introduced for a couple of decades.
Sometimes the AR108 sounds messages that seem to come from high up - FL300-400 perhaps - I take these to be on 8.33 frequencies that slip through its 25 KHz bandwidth. This happens very rarely, though, even if there's plenty of long-distance flights high up over here.

[liam548]

<<I agree with the suggestion of constructing one's own antenna, for non-mobile. But dipoles are less than optimal due to their directiveness.>>

So you hang it up as a vertical dipole, with the wire connected to the braid of the co-ax pointing downwards. That way it becomes omni-directional.

Be forewarned - a lot of cheapo scanners will become overloaded with a more efficient antenna. It won't damage the set, but you may well hear transmissionns which you are not tuned to. Eg a taxi driving past, or the local CB or amateur transmitters may blast through well away from their transmit frequencies.

Lastly, remind yourself of the WT Act: See the sticky on the ATC forum.


Id suggest a notch filter for handheld radios.

[HEATHROW DIRECTOR]

I'm not sure that fitting a notch filter to a hand scanner would a) be possible and b) effective. If the receiver is being swamped due to a wide front-end the only solution is a better designed set which, of course, is available if you want to spend money!!

Ground-plane antenna is a vertical quarter wave with several similar sized rods at the base, fanned out equally. Very simple to construct using an SO-239 socket. However, a vertical dipole is even easier as it just uses two wires and the entire antenna is vertical.

[ChasG]

stevelup - I suppose a teleprinter is out of the question?

I think the problem was the numpty holding the scanner :) having spent more time on it I am getting the hang of it. I might have a look at a better aerial though.

[HEATHROW DIRECTOR]

What would he do with a teleprinter????????????/

[ChasG]

get the messages he couldnt hear on the head phones

[stevelup]

I can hear them, it's you that can't :)

Seriously, you'll get used to it - once you understand it better, you fill in the gaps automatically and it all makes sense.

[HEATHROW DIRECTOR]

<<get the messages he couldnt hear on the head phones>>

And how do those messages get on to a teleprinter (if such an object is available nowadays)?

[liam548]

On my AOR8000 handheld I purchased about 9 years ago I had not choice but to purchase a notch filter as I had a powerful outdoor, high mounted discone antenna attached to it with high quality 1.5cm thick coax.

I did the trick perfectly and I had no breakthrough and was able to hear Manchester ground quite easiily from my bradford base even though the big pennines were between.

No probs using a notch filter with a handheld at home.

[HEATHROW DIRECTOR]

So what form did the notch filter take? Did it plug in to the audio output or was it professionally fitted much farther back in the receiver? If you have interference on audio a notch filter is of little use unless the interference is a single tone or some sort. I suspect your improved receive performance was derived more from the outdoor antenna and good co-ax. However, a simple vertical dipole would work as well, if not better, than an expensive discone, which is trying to be a "jack of all trades".

[ChasG]

Heathrow Director - teleprinter comment was my attempt at humour

[Jim59]

I don't usually have trouble understanding the radio, but some military (MATZ) controllers seem to have some very poor quality microphones or something. Mareham is one of the worst - changing controllers does not seem to make a difference. Cambridge approach/radar, on the other hand, is like listening to radio 4.

[liam548]

So what form did the notch filter take? Did it plug in to the audio output or was it professionally fitted much farther back in the receiver? If you have interference on audio a notch filter is of little use unless the interference is a single tone or some sort. I suspect your improved receive performance was derived more from the outdoor antenna and good co-ax. However, a simple vertical dipole would work as well, if not better, than an expensive discone, which is trying to be a "jack of all trades".

http://a.imageshack.us/img201/9787/260820101122.jpg (http://img201.imageshack.us/i/260820101122.jpg/)


Solid State Electronics in line notch filter. Just goes between the antenna and the antenna input on the scanner. You are then able to "notch" the powerful FM broadbast band (or any other one causing problems) out. Worked very, very well.

[ChasG]

that looks interesting and straightforward thanks.

[HEATHROW DIRECTOR]

Ahhhh.. I think it's misleadingly termed "notch filter". I believe it should more accurately be termed a "band-pass filter". A notch filter is usually employed to remove, or attenuate, a narrow interfering signal but a band-pass filter allows through the range of frequencies you require and attenuates those you not. Anyway, it obviously works so the precise terminology is immaterial.

[liam548]

SSL address

Solid State Electronics (UK) RADIO COMMINCATION & SCANNER ACCESSORIES (http://www.ssejim.co.uk/)