8.33khz options
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A very good question especially since presumably Colibri's fix will not be allowed in case it swamps other nearby 8.33 frequencies.
PS Just reading and digesting the CAA guidance below. Any comments?
Technical information for Ground Stations
Conversion from 25 kHz to 8.33 kHz channel spacing
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Had this discussion at Sywell Rally.....
Spoke to the helpful CAA people and they pointed out that ground stations have another year to comply. So why? Apparently because they are groundbased their range is such that they won't overstep other frequencies in nearby 8.33 spacing. And supposedly they will be encouraged to change sooner as cost of 8.33 licence is cheaper than 25.
Without saying as much, they indicated they expected lots of pilots to be operating illegally for some time to come after start of Jan.
I await Jan 1st eagerly, to see just how many people/places can hear me and how many I can hear!
Without saying as much, they indicated they expected lots of pilots to be operating illegally for some time to come after start of Jan.
I await Jan 1st eagerly, to see just how many people/places can hear me and how many I can hear!
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Spoke to the helpful CAA people and they pointed out that groundj
Without saying as much, they indicated they expected lots of pilots to be operating illegally for some time to come after start of Jan.
I await Jan 1st eagerly, to see just how many people/places can hear me and how many I can hear!
Without saying as much, they indicated they expected lots of pilots to be operating illegally for some time to come after start of Jan.
I await Jan 1st eagerly, to see just how many people/places can hear me and how many I can hear!
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Just got our group PA28 back from its annual with a new Icom A220 fitted in place of our King box. Very modern, large clear display and good sound quality. Went for a first flight with it and quite impressed. When I landed I thought I'd try switching it into 8.33 mode - so into the setup menu select 8.33khz but now it's in set 8.33 I can't seem to get any 25khz frequencies to come up on the display, they just don't exist! Put in Cumbernauld 120.605 fine but then tried Scottish 119.875 & it wasn't there. What am I doing wrong?
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An AM transmission as used on the aircraft band has a single discrete frequency for what is called the carrier. The speech information is carried in what is called sidebands on either side of this carrier frequency. These occupy space, typically 5 kHz either side. The receiver has a filter that is typically 10khz wide, so if you set your receiver to a frequency of 120.000 MHz, the filter allows the receiver to hear anything from 119.995 to 120.005. As long as the station you want is within this band, you will hear it. The same applies to the ground station, so if they are set to 120.000 they will hear anything transmitting plus or minus say 5 kHz from that frequency. Filter bandwidths for 8.33 radios will be much narrower, allowing more stations to use the same chunk of frequency space.
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According to my reading of CAP1573, 119.875 will be a 8.33 kHz frequency, although 119.880 will be displayed. Have you tried that?
25 khz freqs will still be 25khz freqs and will be selectable as before on your new 8.33/25khz radio(unless you have an IcomA220 which is a bit more difficult as explained in earlier post)
Good reading here to explain:
http://www.lightaircraftassociation..../May/radio.pdf
The table requires a good look to understand that your new 8.33 radio is in fact dual 8.33/25.....and your old 25 will work just fine on those freqs....which begs the question as to why we are not supposed to use them!
Oh... and CAP1573 says
"The licensing fee charged by Ofcom for an 8.33 kHz radio licence will be significantly less than the 25
kHz licence fee, due to the reduced bandwidth occupied." Yea right....... more like blackmail!
Last edited by arelix; 15th Sep 2017 at 15:49.
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There is a lot of misunderstanding on the 8.33 issue. 119.875 is a 25 freq
25 khz freqs will still be 25khz freqs and will be selectable as before on your new 8.33/25khz radio(unless you have an IcomA220 which is a bit more difficult as explained in earlier post)
Good reading here to explain:
www.lightaircraftassociation.co.uk/2013/Magazine/May/radio.pdf
The table requires a good look to understand that your new 8.33 radio is in fact dual 8.33/25.....and your old 25 will work just fine on those freqs....which begs the question as to why we are not supposed to use them!
Oh... and CAP1573 says
"The licensing fee charged by Ofcom for an 8.33 kHz radio licence will be significantly less than the 25
kHz licence fee, due to the reduced bandwidth occupied." Yea right....... more like blackmail!
25 khz freqs will still be 25khz freqs and will be selectable as before on your new 8.33/25khz radio(unless you have an IcomA220 which is a bit more difficult as explained in earlier post)
Good reading here to explain:
www.lightaircraftassociation.co.uk/2013/Magazine/May/radio.pdf
The table requires a good look to understand that your new 8.33 radio is in fact dual 8.33/25.....and your old 25 will work just fine on those freqs....which begs the question as to why we are not supposed to use them!
Oh... and CAP1573 says
"The licensing fee charged by Ofcom for an 8.33 kHz radio licence will be significantly less than the 25
kHz licence fee, due to the reduced bandwidth occupied." Yea right....... more like blackmail!
"If you accidentally select 132.005 when you should have selected 132.0
you will be on the right frequency but with a
narrower bandwidth, but the chances are that
you will be able to communicate. But if you
select 132.0 when you should be on 132.005
your radio will be in 25kHz mode and you are
likely to cause interference on several 8.33
channels and you may hear transmissions from
adjacent frequencies."
If you can communicate with a 25kHz Ground Station by selecting the nearest 8.33kHz frequency, then maybe the current ICOM A220T is set up the best way. You can continue to operate in 25kHz mode until the end of this year and then switch to 8.33kHz mode so that you do not interfere with any distant ground stations on adjacent 8.33kHz frequencies when you transmit.
If communication with a particular 25kHz ground station fails, you can temporarily switch back to 25kHz mode in the air. This will no longer be necessary when all ground stations eventually switch to 8.33kHz.
Is this summary correct, or have I missed something?
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8.33 radios ATC will ask you to set channel 118.405 You select CHANNEL 118.405
The transmitted frequency is 118.400
With regard to 121.5 the selected channel will be 121.505 transmitting on 121.500
The whole situation is a bit of a dogs dinner.
The transmitted frequency is 118.400
With regard to 121.5 the selected channel will be 121.505 transmitting on 121.500
The whole situation is a bit of a dogs dinner.
Last edited by Robin400; 15th Sep 2017 at 20:13. Reason: no change
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My new 8.33 radio has a channel spacing option.
a) 8.33/25 kHz
b) 25 kHz.
The first thing I did was select option b) to disable the 8.33 feature so that when tuning it is simpler and quicker since the 8.33 channels are bypassed. A lot of money for nothing!
a) 8.33/25 kHz
b) 25 kHz.
The first thing I did was select option b) to disable the 8.33 feature so that when tuning it is simpler and quicker since the 8.33 channels are bypassed. A lot of money for nothing!
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Theory is all very well but what about in practice:
Just tried my Yaesu portable in 8.33kHz mode and can clearly pick up 118.800 and 119.100 on 118.805 and 119.105 respectively, although I noticed that a higher signal level is required to open the squelch on 118.800.
Obviously, I did not transmit but have previously picked up 120.605 transmissions with my 25kHz radio in the aeroplane set to 120.600 so hopefully, a 25kHz ground station would be able to pick up my transmissions on the nearest 8.33 kHz frequency. I will try that the next time I fly,
Just tried my Yaesu portable in 8.33kHz mode and can clearly pick up 118.800 and 119.100 on 118.805 and 119.105 respectively, although I noticed that a higher signal level is required to open the squelch on 118.800.
Obviously, I did not transmit but have previously picked up 120.605 transmissions with my 25kHz radio in the aeroplane set to 120.600 so hopefully, a 25kHz ground station would be able to pick up my transmissions on the nearest 8.33 kHz frequency. I will try that the next time I fly,
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Just to try and simplify matters that have been brought up in this thread.
The new 8.33 kHz frequencies are essentially interwoven with the 25 kHz frequencies that have been used for years previously.
Unfortunately the digital frequency displays don't do the thirds rounding of frequencies that well, so the frequency on the display may be slightly off from the frequency your radio is actually tuned to.
The newer 8.33 kHz radios have narrower filters fitted in the transmit and receive circuits. This makes accurate tuning more critical if you are to be able to receive or transmit on a particular frequency.
Visually the difference is like looking at the world through a panoramic window, or through a series of smaller windows with shutters that only let you look at the view through one window at a time. The whole view is still available, its just that you have to focus on a narrower view in any particular direction than taking it all in at once.
In the case of trying to tune one of the old 25kHz frequencies, you may have to tune one channel above or below the frequency you would expect to be displayed in order to make contact. This is because your receiver has a much narrower bandwidth. You need to have the carrier frequency of the ground transmitter inside your receiver bandwidth to be able to hear the ground station.
Ground stations using 25 kHz equipment should still hear your transmissions okay because their receivers are tuned to a wider bandwidth. The issue here is that a ground station might hear you transmitting clearly, but you can't hear them because your receiver is not tuned to their carrier frequency.
Your transmissions will appear quieter and with more background noise, compared to an old 25 kHz radio. That is because your signal is not filling the entire receiving bandwidth of the ground station receiver, so you may find reduced transmitter range is a problem.
When ground stations are updated with new equipment, the quieter signal problem will disappear because now both stations will be using equipment that is closely matched in bandwidth for transmitting and receiving.
Yes, there will be some teething problems and issues and combinations of old and new equipment are used on the ground and in the air. These problems will sort themselves out as everyone moves to comply with the new standards.
Using old 25 kHz filtered equipment will cause interference to other users and you will quite probably be unaware of it. Of course you callsign will give you away, so sooner or later someone official will no doubt make you aware of the issue.
Nobody likes change and epecially the sort that requires a fair sum of money to sort out, but the new equipment does work well and will work even better once everyone has switched to the new standard.
The new 8.33 kHz frequencies are essentially interwoven with the 25 kHz frequencies that have been used for years previously.
Unfortunately the digital frequency displays don't do the thirds rounding of frequencies that well, so the frequency on the display may be slightly off from the frequency your radio is actually tuned to.
The newer 8.33 kHz radios have narrower filters fitted in the transmit and receive circuits. This makes accurate tuning more critical if you are to be able to receive or transmit on a particular frequency.
Visually the difference is like looking at the world through a panoramic window, or through a series of smaller windows with shutters that only let you look at the view through one window at a time. The whole view is still available, its just that you have to focus on a narrower view in any particular direction than taking it all in at once.
In the case of trying to tune one of the old 25kHz frequencies, you may have to tune one channel above or below the frequency you would expect to be displayed in order to make contact. This is because your receiver has a much narrower bandwidth. You need to have the carrier frequency of the ground transmitter inside your receiver bandwidth to be able to hear the ground station.
Ground stations using 25 kHz equipment should still hear your transmissions okay because their receivers are tuned to a wider bandwidth. The issue here is that a ground station might hear you transmitting clearly, but you can't hear them because your receiver is not tuned to their carrier frequency.
Your transmissions will appear quieter and with more background noise, compared to an old 25 kHz radio. That is because your signal is not filling the entire receiving bandwidth of the ground station receiver, so you may find reduced transmitter range is a problem.
When ground stations are updated with new equipment, the quieter signal problem will disappear because now both stations will be using equipment that is closely matched in bandwidth for transmitting and receiving.
Yes, there will be some teething problems and issues and combinations of old and new equipment are used on the ground and in the air. These problems will sort themselves out as everyone moves to comply with the new standards.
Using old 25 kHz filtered equipment will cause interference to other users and you will quite probably be unaware of it. Of course you callsign will give you away, so sooner or later someone official will no doubt make you aware of the issue.
Nobody likes change and epecially the sort that requires a fair sum of money to sort out, but the new equipment does work well and will work even better once everyone has switched to the new standard.
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Instructions taken from a 8.33 radio manual.
Channels used with 25kHz width are entered in multiples of 25kHz: 123.500, 123.525, 123.550, 123.575, 123.600 etc. These are compatible with the old 25 kHz-only radios. To use the same frequencies with 8.33 kHz width, the frequency values entered are increased by 5kHz: 123.505, 123.530, 123.555, 123.580, 123.605 etc.
Channels used with 25kHz width are entered in multiples of 25kHz: 123.500, 123.525, 123.550, 123.575, 123.600 etc. These are compatible with the old 25 kHz-only radios. To use the same frequencies with 8.33 kHz width, the frequency values entered are increased by 5kHz: 123.505, 123.530, 123.555, 123.580, 123.605 etc.
I've had direct experience of this problem. When 8.33 channels were introduced, for upper airspace in Europe, I was flying Boeing 747s. The radio tuning "Gables" heads were swapped with almost identical units that allowed the extra digit to be selected on the concentric switch which had grown from 2 to 3 levels.
Heading back over the Med early one morning Malta gave me a new channel to call Marseille but even though there were two of us looking at the "frequency" I still managed to miss-select it by one click.
The result was neither of us could here each other clearly. He kept saying "ooiscallin?" and I couldn't make proper contact as the garballing was severe.
Luckily P2 was more awake and quickly clicked over one more notch and we were able to hear ATC clearly. Thus getting both air and ground stations to "match" their frequencies is going to be the new game come Jan 1st.
Heading back over the Med early one morning Malta gave me a new channel to call Marseille but even though there were two of us looking at the "frequency" I still managed to miss-select it by one click.
The result was neither of us could here each other clearly. He kept saying "ooiscallin?" and I couldn't make proper contact as the garballing was severe.
Luckily P2 was more awake and quickly clicked over one more notch and we were able to hear ATC clearly. Thus getting both air and ground stations to "match" their frequencies is going to be the new game come Jan 1st.
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To keep this simple and avoid loss of comms all we have to understand is that the
(channel) we set on a 8.33 radio is not the frequency that the radio transmits on.
When ATC say " call CHANNEL xxx.xxx set the numbers normal manner.
The radio will not transmit the numbers you have displayed, that is why it is called a CHANNEL
Marine vhf has always used CHANNELS. I think the basic calling CHANNEL is 16, have not a clue
what the actual frequency is.
I posted a link which shows the set/displayed value and the frequency that the radio actually
transmits on.
(channel) we set on a 8.33 radio is not the frequency that the radio transmits on.
When ATC say " call CHANNEL xxx.xxx set the numbers normal manner.
The radio will not transmit the numbers you have displayed, that is why it is called a CHANNEL
Marine vhf has always used CHANNELS. I think the basic calling CHANNEL is 16, have not a clue
what the actual frequency is.
I posted a link which shows the set/displayed value and the frequency that the radio actually
transmits on.
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Robin400
The Marine Distress Frequency Channel,16 is 156.8 MHz. Early marine band VHF radios were all crystal controlled and the frequencies and mode of transmission (frequency modulation (FM)) was chosen to prevent interference to airband transmissions and also direct communication between ships and aircraft. Aircraft use amplitude modulation or AM and the two systems are technically incompatible. There was some military reason for doing that at the time, although the reasoning is lost in the mists of time.
When digitally synthesised equipment became available, more marine channels were slotted in between the existing ones to make old and new equipment compatible. Looking at the actual frequencies against a list of channel numbers makes no sense at all as the frequencies hop about all over the place as the frequencies go up from Channel 0.
Additionally, marine radio systems are capable of full duplex transmisson and reception on some channels to enable virtually normal telephone conversations to be carried out. These channel pairings require the transmitter and receiver frequencies to be as widely spaced as possible because the transmitter and receiver sections are operating simultaneously. Tight filtering and some clever technical work arounds are needed to allow the system to work. The same full duplex system also works and is used on marine short wave frequencies but is somewhat more prone to interference. Simplex transmissions are more usually used for this reason.
As far as airband systems go, selecting the correct channel or frequency is more critical now, but otherwise the equipment functions just as it did before.
The Marine Distress Frequency Channel,16 is 156.8 MHz. Early marine band VHF radios were all crystal controlled and the frequencies and mode of transmission (frequency modulation (FM)) was chosen to prevent interference to airband transmissions and also direct communication between ships and aircraft. Aircraft use amplitude modulation or AM and the two systems are technically incompatible. There was some military reason for doing that at the time, although the reasoning is lost in the mists of time.
When digitally synthesised equipment became available, more marine channels were slotted in between the existing ones to make old and new equipment compatible. Looking at the actual frequencies against a list of channel numbers makes no sense at all as the frequencies hop about all over the place as the frequencies go up from Channel 0.
Additionally, marine radio systems are capable of full duplex transmisson and reception on some channels to enable virtually normal telephone conversations to be carried out. These channel pairings require the transmitter and receiver frequencies to be as widely spaced as possible because the transmitter and receiver sections are operating simultaneously. Tight filtering and some clever technical work arounds are needed to allow the system to work. The same full duplex system also works and is used on marine short wave frequencies but is somewhat more prone to interference. Simplex transmissions are more usually used for this reason.
As far as airband systems go, selecting the correct channel or frequency is more critical now, but otherwise the equipment functions just as it did before.