Air Distress - Now 121.505 MHz ?

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Re: Air Distress - Now 121.505 MHz ?

Postby Minus1 » Fri Oct 19, 2018 10:00 am

Mark5R wrote:
Minus1 wrote:The numbers given for 8.33 kHz channels are CHANNELS they are NOT frequencies. They are NOT 5 kHz steps.

"128.855" is an 8.33 kHz bandwidth channel using a frequency of 128.85 MHz.
"128.85" is a 25 kHz bandwidth channel also using 128.85 MHz


I do hear what you are saying but at the risk of sounding dumb I still don't get it. How can 128.855 be a channel name? It makes no sense.

There are one or two pages NATS have updated to the new steps. Taking Leeds Bradford as an example they list the following

LEEDS APPROACH 134.580 MHz

Surely they are referring to the frequency in MHz as 134.580 MHz and not a channel name?


They haven't had the sense to explain to people what the hell is going on.
They just just a number, without explaining that it is a CHANNEL not a FREQUENCY.
Because the channel looks like a frequency, people do not understand.

"16" is the channel number for VHF Marine calling frequency of 156.8 MHz, but because "16" does not look like a frequency, people do not get confused.
If they had been stupid and called the channel "156.16", people would get confused.

Common sense was more prevalent in the good old days. :rolleyes:
I reserve the right to ignore people who have made no attempt to the read the manual, and expect others to do it for them.
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Re: Air Distress - Now 121.505 MHz ?

Postby Scan125 » Fri Oct 19, 2018 12:29 pm

m0lsx wrote:That is a silly thing to say, of course you can dial in an 8.33khz channel. Even a very basic radio will be capable of that.


I didn't say you can't dial in an 8.33kHz channel did I? With the wheels available you can't dial in an 8.33kHz FREQUENCY VALUE.
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Re: Air Distress - Now 121.505 MHz ?

Postby radiostationx » Fri Oct 19, 2018 7:35 pm

This thread has attracted many viewpoints but to perhaps clarify.
Under ICAO rulings only six numbers can be conveyed as a frequency irrespective of if its 8.33 spacing, the channels idea was ditched for some reason.
I suppose the 6 number rule is to prevent confusion in the air plus as was said previously some radio packs are not equipped with enough adjustments for such fine tuning.

A B777 twin dial nav/comms radio panel is far different from a more modern B787 one which has combined VHF and HF, numeric keypad the lot.
Both tune to 8.33 but over the air 6 digits are used and those same 6 digits are on the display.
Here is a B787 and B777 office comapred, the radios (one each for capt and 1st officer) are in the first row below the red fuel flow cut off switch covers.
You definitely dont want to knock them accidentally when tuning around looking for 8.33, hence the covers ! :smiles:

The 777 on the right, the skippers is set to VHF mode 1 and he/she has a third radio on the skippers side usually for HF here its on VHF mode 3 with acars data on the primary and 132.3 in the standby, perhaps for oceanic clearance.
Sometimes there is an HF in the overhead so you can leave that on SELCAL watch for long crossings.
The newer 787 has a multi type comms/nav management combined module in the middle.
I think any of the 3 or 4 radios on 777/787 can use HF and go though the tuner.

Image

The 6 digit ICAO rule prevents the seventh figure being used in 8.33 spacings.

ICAO
Amendment 80 to ICAO Annex 10, Volume II

Amendment 80 to ICAO Annex 10, Volume II - Aeronautical Telecommunications - becomes applicable on 24 November 2005. It introduces a procedure requiring all VHF voice communication channels to be indicated by the use of 6 digits
(4 digits for the case of channels ending in two zeros), irrespective of whether 25 or 8.33 kHz channel spacing is used, e.g.:

- 118,005 specified as "ONE ONE EIGHT DECIMAL ZERO ZERO FIVE"
- 118,025 specified as "ONE ONE EIGHT DECIMAL ZERO TWO FIVE"
- 118,100 specified as "ONE ONE EIGHT DECIMAL ONE"

-The use of the term "CHANNEL" for 8.33 kHz channels is discontinued.




Further reading

https://web.archive.org/web/20071027160059if_/http://www.eurocontrol.int/vhf833/gallery/content/public/Amendment%20to%20ICAO%20Annex10%20VolumeII_p5-11p5-12.pdf
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Re: Air Distress - Now 121.505 MHz ?

Postby Scan125 » Fri Oct 19, 2018 10:40 pm

Thanks radiostationsx.

What you have provided technical links to substantiates my humble offering / explanation of the 6 digit tuning abilities. You have also revealed that in some some modern aircraft there may be more than 6 digit dial ability but the 7th / 8th are "guarded" for sensible reasons.

Not your fault but the Amendment 80 to ICAO Annex 10, Volume II document link you provided does not explain the real relationships between channels, Pilot/ATC tuning instructions (read what to set on your radio kit) and the actual frequencies used. In fact for pilots and ATC they don't need to know what the actual frequencies are. If they did that might add even more confusion and induce errors.

I think people need to understand that pilots/ATC play by the "book". A flight crew when faced with a flight malfunction will reach for "the book" for that aircraft and follow the prescribed instructions to the letter regardless of what they may otherwise think. It is called "standard operating procedures". Radio comms follow standard operating procedures. Neither ATC or pilots need to know if an *actual* frequency of 118.000 or 918.00 is used when they set 118.000.

For scanner and other non official aircraft kit users we get confused and hence all the round robin discussions.

If you take Marine or CB radio kit the units work in channels number of 00 to nn. Clear, precise and controlled. The typical scanner user (excluding scanning marine/CB kit) will be working in absolute frequencies. We have conversion charts of channel vs frequency. Come airband such conversion charts are not so prevalent AND because when only the 25MHz steps were involved and the so called channel to frequency mappings were exact (i.e. channel dial settings = exact frequency) the lay person is thus totally confused when the 25kHz band steps get split up into 8.33kHz steps.

It is what it is so we just have to get our heads around it and accept it a gospel truth even though logic might dictate otherwise.

Maybe the radio comm dials should have been labelled A to J so 118.000 would be BBI.AAA (bravo bravo india decimal alfa alfa alfa) :)
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Re: Air Distress - Now 121.505 MHz ?

Postby Frequency Hopper » Mon Oct 22, 2018 3:11 pm

Would members agree that the following link is accurate?

http://g3asr.co.uk/calculators/833kHz.htm

And if so, does that mean that all frequencies follow the same pattern as these...?

118.000 is now said as 118.005 (channel name) which is the actual frequency of 118.0000

New channel 118.010 (channel name) is the actual frequency of 118.0083

New channel 118.015 (channel name) is the actual frequency of 118.0166

118.0250 is now said as 118.030 which is still the actual frequency of 118.0250

Is all that correct?
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Re: Air Distress - Now 121.505 MHz ?

Postby Scan125 » Mon Oct 22, 2018 7:09 pm

Frequency Hopper wrote:Would members agree that the following link is accurate?

http://g3asr.co.uk/calculators/833kHz.htm

And if so, does that mean that all frequencies follow the same pattern as these...?

118.000 is now said as 118.005 (channel name) which is the actual frequency of 118.0000

New channel 118.010 (channel name) is the actual frequency of 118.0083

New channel 118.015 (channel name) is the actual frequency of 118.0166

118.0250 is now said as 118.030 which is still the actual frequency of 118.0250

Is all that correct?


Yes .... sort of.

Firstly the Controller says 118.005 and the frequency to set on the receiver is 118.000. NOTE the pilot will actually set 118.005 on his transceiver and not 118.000. If you have a non certified/aligned airband receiver/transceiver then you will set 118.000.

Secondly. The list you referenced does not include for example 118.095 which may not commonly be called but speaking to my brother, a retired BA Senior Captain with well over 20K flying hours, when I read the .005 to 090 to his he said "what about 095". Now he freely admits it is some 10 years since he flew and he may be recalling incorrectly but it is interesting that he picked up on 095 so something from his past caused this so it is possible that 095 was/is still called by ATC.

He also says that when ATC call "contact xyz on 118.nnn" as a pilot he cares not as long as when he dials 118.nnn into his aircraft radio he can make contact with someone at that designated contact point. As far as he is concerned if 500.nnn Mhz actual frequency was used or the aircraft radio kit sent the signal on a satellite channel at x GHz it is basically irrelevant from the cockpit to cockpit or cockpit to ground control point of view. ONLY when things do not function as expected do they reach for the bible of procedures etc. behind the seat.

I've joked with my brother many a time that he is just a glorified bus driver and actually these commercial pilots are very modest, focused on what matters, and can/do "stick to the job and procedures". Where we as public, despite taking the piss, we never ever get to see the compulsory simulator tests they go through which will test the "response and actions based on the book/bible for that aircraft and required flight skills" down/through to "new adventures" possibly outside of normal scope. And on this and simulator testing/training it is perfectly possible to ensure everyone fails and crashes without question. Everyone and everything can be overloaded well beyond acceptable stress limits. So why have I just said this last piece. Simply because 118.nnn is what the crew set. Has to be clear, precise and unambiguous. A very small item/step in the list of what they have to do and focus on at any one given time.

It is us amateurs down here fussing over 118.005 or 118.000 etc. etc.

I believe my frequency list as detailed here: https://www.nick-bailey.co.uk/scan125/M ... .html#48.1

is correct and covers the full 000 to 095 possibilities regardless of if anyone nnn is actually used or called. It could be that in some other countries or remote locations they choose an abc that not usually used in the EU. Regardless the aircraft radio kit has to tune to the actual frequency of 118.0916 regardless of whether 118.090 or 118.095 is dialled into the aircrafts radio.

If you want to be perfectly aligned with ATC/Airband then use dedicated certified air band/aircraft radio kit so when ATC say 118.nnn and you dial 118.nnn then you will be on the correct frequency be it 188, 588 or 988 etc.
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Re: Air Distress - Now 121.505 MHz ?

Postby Minus1 » Tue Oct 23, 2018 8:15 am

They don't list 25 kHz bandwidth frequencies at all!

119.0 may still exist as a 25 kHz bandwidth frequency in some places.

In some places it may have been replaced by THREE 8.33 kHz channels:
"118.990" (actually 118.99166)
"119.005" (actually 119.0)
"119.010" (actually 119.00833)

It is interesting to ponder whether "117.990" (117.99166) will be used anywhere...
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Re: Air Distress - Now 121.505 MHz ?

Postby FreqFreak » Sat Oct 27, 2018 7:57 pm

Doubt any radios actually tune below 118.000
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Re: Air Distress - Now 121.505 MHz ?

Postby radiostationx » Sat Oct 27, 2018 8:49 pm

Most probably do tune that low, but by accident.
The components & tolerances used for hobby/amateur grade radios are not exactly straight from the quartermasters stores at Watkins Johnson or Rohde-Schwarz. Each model signed off with its own certificate of conformance & alignment ? In our Dreams..

Aircraft/Ground transmitters have, They are safety critical items.
Usually they are removed from the aircraft/tower or whatever as a module & periodically serviced to ensure frequency stable comms to factory specs by specialist engineers using test gear worth hundreds of thousands of £s. A test signal genny can cost north of £90k for a start.

I have seen some of the removed modules, more signatures, stickers and document records than you could shake a big stick at.

When we see 118.000 on the screen our radios, we tend to believe it, the fact is it (the amateur grade radio) is probably "lying".
Its by how much its "lying" which determines good from bad or new from old.
For example electrolytic capacitors, even good ones by Panasonic,Nichicon & Elna have an expected service life of around 10 yrs before they get leaky/wobbly so if they are on a supply for a txco circuit, that can cause "lying".
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Re: Air Distress - Now 121.505 MHz ?

Postby Scan125 » Sat Dec 15, 2018 12:37 pm

Well Santa is bringing me a Yaesu FTA-250L Airband Transceiver for Christmas.

This is a pucker 25/8.33 compliant unit supplied by Bournemouth Avionics.

I'll be able to do back to back comparisons with my UBC125XLT etc.

Once I get to understand the beast better I may look doing Scan125 like software for it. Yaesu have already given me the bad news that they do not/will not disclose their programming API so it could turn out to be hard and time consuming work probing the FTA-250L. With the UBC125XLT at least I had a little bit of a head start as Uniden published a limited API for the BC125AT. That left me to probe the UBC125XLT for its extra commands and the all important "other" commands not published by Uniden that allowed me to do the full remote and virtual control of the scanner.
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