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Airband VHF listening 135.585 Northern high level freq.

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Airband VHF listening 135.585 Northern high level freq.

Old 15th Aug 2019, 23:42
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Airband VHF listening 135.585 Northern high level freq.

Been a life long airband listener...with a break of a few years...been listening to the Northwest high-level freq of 135.585.

A few odd things I don't understand about this freq.

With the aid of Flight Radar I hear transatlantic flights log onto the freq near the midlands but once they seem to reach the cruise altitude I hear nothing else from the aircraft or the ground controllers calling these aircraft...don't ever hear them giving instructions to change to the next sector freq.

I listened to 2 Fed Ex flights come onto this freq 135.585 as they approached the Midland around 70 miles from each other route southeast of Manchester and coast out near Southport just North of Liverpool but bar the first few communications when coming on the freq I hear no more...not ever an interaction to change to the next en-route freq.

What should this be...my antenna is a roof-mounted dipole and I live on high ground with a good horizon...I can hear high flying aircraft over 150miles plus away on my radio so they are not out of range...?

Also is 135.585 a freq that is re-broadcasted...doesn't sound like a direct transmission from the aircraft....bit tinny sounding.

Last edited by magpienja; 16th Aug 2019 at 09:13.
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Old 16th Aug 2019, 00:25
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Originally Posted by magpienja View Post
Been a life long airband listener...with a break of a few years...been listening to the Northwest high-level freq of 135.585.

A few odd things I don't understand about this freq.

With the aid of Flight Radar I hear transatlantic flights log onto the freq near the midlands but once they seem to reach the cruise altitude I hear nothing else from the aircraft or the ground controllers...don't ever hear them giving instructions to change to the next sector freq.

I listened to 2 Fed Ex flights come onto this freq 135.585 as they approached the Midland around 70 miles from each other route southeast of Manchester and coast out near Southport just North of Liverpool but bar the first few communications when coming on the freq I hear no more...not ever an interaction to change to the next en-route freq.

What should this be...my antenna is a roof-mounted dipole and I live on high ground with a good horizon...I can hear high flying aircraft over 150miles plus away on my radio so the are not out of range...?

Also is 135.585 a freq that is re-broadcasted...doesn't sound like a direct transmission from the aircraft....bit tinny sounding.
Airways frequencies are often transmitted from more than one site, each site transmitting slightly 'off' the main frequency so as not to interfere with the other and with 8.33 kHz spacing that means it is transmitted on a very narrow frequency band hence the tinny sound.
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Old 16th Aug 2019, 06:25
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CPDLC?

https://www.skybrary.aero/index.php/...ations_(CPDLC)
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Old 16th Aug 2019, 07:46
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You say you use a dipole - vertically mounted I trust? If it is horizontal it would havew directional properties.
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Old 16th Aug 2019, 09:07
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Hi HD...yes vertically polarized so Omnidirectionally.

Its crossed my mind that once at cruise alt the North America bound aircraft communicate via there data link....odd that they dont report QSY the freq.
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Old 16th Aug 2019, 09:09
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Sorry Squawk 6042...I had not read your link when I posted my last.
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Old 16th Aug 2019, 13:00
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Originally Posted by magpienja View Post
Hi HD...yes vertically polarized so Omnidirectionally.

Its crossed my mind that once at cruise alt the North America bound aircraft communicate via there data link....odd that they dont report QSY the freq.
Squawk 6042 may well have it - If flights are operating CPDLC then you won't hear a voice "QSY" (I'm not a radio amateur but I believe that means a read back of frequency going to? as in "contact Shannon on ...")..

How it works with CPDLC on board is that the new frequency gets sent up to the aircraft by datalink, the crew do a datalink acknowledgement of that change and then they switch frequency, no voice call on the old frequency, onto the new VHF freq.

Once you get to the new frequency you still check in by voice, and then if still CPDLC you may well go silent again ( as far as VHF voice is concerned)...

All the above may well explain why you are only hearing traffic on the initial call as they enter the sector you are listening to.
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Old 16th Aug 2019, 14:13
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All sounds about right Wiggy.

Only seems as far as I can see applies to a/c that is going to route across the Atlantic.

Yes your quite right QSY= change freq.

I am also a keen HF radio airband listener...but not as much to listen to these days with the advent of the data link...but they do still check-in.
Seems data link is not always a reliable link via data as I often hear the controller call an aircraft out over the ocean to say you link has failed...so old school technology still works when modern doesn't.
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Old 16th Aug 2019, 17:59
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Originally Posted by magpienja View Post
All sounds about right Wiggy.

Only seems as far as I can see applies to a/c that is going to route across the Atlantic.
That might be because it's (possibly) more likely a Long Haul type will have CPDLC and have it logged on whilst overflying domestic airspace, vs a short haul flight doing a short domestic sector where CPDLC might actually complicate matters.

If you could monitor ATC elsewhere in the world you'd hear a similar "silent change" process pretty much anywhere when leave a CPDLC sector or change from one CPDLC sector to another, e.g; when crossing the boundary between say Gander and Moncton, or closer to home switching sectors in Maastricht airspace...



And yes, sometimes the gremlins creep in and you either have to re-log on or revert "to voice".

Last edited by wiggy; 16th Aug 2019 at 18:20.
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Old 16th Aug 2019, 18:09
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I see....very informative thank you.
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Old 23rd Aug 2019, 02:41
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All the above absolutely correct ref CPDLC. London and Scottish (and indeed most of Europe) now use CPDLC in the upper areas (above FL195) and aircraft equipped with the system are encouraged to log on. ATC can sent all sorts of instructions (e.g. climb, descent, heading, speed, direct-to) as well as frequency changes. Think of it like a smart form of text messaging. The protocol for frequency changes is to ACCEPT the CPDLC frequency chance via a flight deck selection and then voice call in on the new frequency. Hence you are only hearing the initial call. The main advantages are keeping radio traffic down on busy frequencies and eliminating transposition errors/mis-hearing of frequencies or other instructions. I recently flew from London to Seattle and was CPDLC from about FL200 in the climb out of LHR until entering the USA in descent from Vancouver FIR.

One of CPDLCs great benefits is it can create a pseudo-radar environment for air traffic controllers for FIRs covering very sparsely populated or vast areas where fitting of radar heads is impossible or impractical. Hence it is used over the Atlantic, Canada and large areas of Africa.

In the North Atlantic (NAT) region the use of ADS-C and CPDLC are mandatory for operations between FL350 and FL390 so most long haul aircraft are now equipped with it. The system makes automatic position reports amongst other things eliminating the need for difficult HF communications. Not having it means FL350-FL390 is not available so most longhaul aircraft have it fitted these days. CPDLC will be soon be mandated in Eurocontrol upper airspace so shorthaul aircraft are getting it now as well.
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Old 23rd Aug 2019, 09:20
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Thank you for that explanation...progress but those on the ground who enjoy listening to airband won't be overjoyed.

Can a controller get an instant response on VHF voice I wonder if he needs to...or is the a/c VHF muted like HF till its woken up by selcal?
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Old 23rd Aug 2019, 10:44
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We’ll go headset off on HF once SELCAL is checked. Headset remains on with VHF/CPDLC only. Actually not sure what the legal position is but that’s our SOPs.
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Old 23rd Aug 2019, 12:03
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I see thank you.

I expect most commercial pilots find HF a bind...I'm a licenced UK Amature Radio Operator and love HF.

I can imagine HF for you during our sunspot minima at present can be difficult.
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Old 23rd Aug 2019, 12:10
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Originally Posted by magpienja View Post
Can a controller get an instant response on VHF voice I wonder if he needs to...or is the a/c VHF muted like HF till its woken up by selcal?
Yes, on VHF it's headsets on and listening watch. The use CPDLC helps to keep routine stuff like frequency changes off the radio, freeing up space for more important instructions. A lot of controllers use it that way.
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Old 31st Aug 2019, 20:45
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I assume an instruction from ATC sent via CPDLC will be received only by the aircraft for which the instruction is intended, and if so isn't it the case that a vital component of situational awareness is lost if , say aircraft A is instructed to turn/climb/descend etc and adjacent aircrafts B, C, D etc cannot now know what A is doing?

As an aside, I well remember listening in on HF and being astonished how many attempted calls were unanswered, presumably due to poor propagation.

'Santa Maria, Santa Maria Reach XYZ position over'
30 seconds later...
'Santa Maria, Santa Maria Reach XYZ position over'
30 seconds later...
'Santa Maria, Santa Maria Reach XYZ position over'
30 seconds later...
'Reach XYZ nothing heard, out'.
(Reach btw I gather was commonly used as a USAF callsign.)

On the other hand, one morning 7 am here in the UK I heard a flight calling ATC somewhere in South America (Paramaribo I think) with surprising clarity on a Yeasu FRG7700 with random wire aerial (antenna!).

Last edited by Ant; 31st Aug 2019 at 21:02.
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Old 1st Sep 2019, 00:53
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Originally Posted by wiggy View Post
Squawk 6042 may well have it - If flights are operating CPDLC then you won't hear a voice "QSY" (I'm not a radio amateur but I believe that means a read back of frequency going to? as in "contact Shannon on ...")..

How it works with CPDLC on board is that the new frequency gets sent up to the aircraft by datalink, the crew do a datalink acknowledgement of that change and then they switch frequency, no voice call on the old frequency, onto the new VHF freq.

Once you get to the new frequency you still check in by voice, and then if still CPDLC you may well go silent again ( as far as VHF voice is concerned)...

All the above may well explain why you are only hearing traffic on the initial call as they enter the sector you are listening to.
After logon..... Shanwick sends a message "Shanwick advises higher may be available" ........Lies Lies Lies !
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Old 1st Sep 2019, 11:13
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The FRG-7700 had one of those many years ago Ant...nice radio...I use the FT-450d now.

Yes radio propagation...a fickle thing.
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Old 2nd Sep 2019, 21:45
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Ah, the Froggie 7700... been looking at photos, bought mine 30 years ago with VHF converter and antenna tuner, later sold to move to a Trio/Kenwood R5000. Nostalgia!!
Long gone now, but still use a Fairmate HP100 and an Icom IC-R5.
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Old 3rd Sep 2019, 07:30
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My FRG-7700 is long gone...bought an older FRG-7 sometime later...I still have that and it works fine.

But I went in for my amateur radio licence some years ago...I use an FT-450d transceiver now...has full general coverage receive.

Still, find radio fascinating after more than 50 years.
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