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Frequencies and 8.33 Channel numbers

 
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JonathanMilbank



Joined: 14 Apr 2012
Posts: 277
Location: Aberdeen area

PostPosted: Sun Jul 21, 2019 2:29 am    Post subject: Frequencies and 8.33 Channel numbers Reply with quote

Our airfield has just been assigned its own frequency 118.275 MHz, with associated 8.33 Khz channel number 118.280. Club members queried the numerical difference, so herewith a short list of VHF radio frequencies and their corresponding channel numbers. This was created by way of explaining why Longside airfield has been assigned Channel 118.280, yet will operate on frequency 118.275 MHz.

The old 25 KHz separated frequencies are shown in bold and it should be appreciated that while a new 8.33 KHz aircraft radio is capable of operating on the old frequencies, when in 8.33 mode the bandwidth of those old frequencies has been narrowed to enable two new 8.33 frequencies to be inserted between each pair of old ones. There is a penalty for narrow bandwidth, which is that speech quality is a bit poorer.

If someone were to transmit using the old 25 KHz frequencies, communication would still work but the wider bandwidth would spill over and interfere on adjacent 8.33 KHz channels.

To discriminate between the old 25 KHz frequencies and their corresponding new 8.33 channel numbers, radio manufacturers have added a '5' or a '0' in the third decimal position on the aircraft radio display. This is why, as an example, it is possible to mistakenly select channel 134.105 and yet still be able to communicate with Aberdeen Offshore which continues to operate on frequency 134.1 MHz. The result is a slight "mismatch" with poorer comms for both parties, which someone more knowledgeable would be able to explain.

So when ATC gives you an instruction to change to Radar 119.055, you probably won't hear the word 'frequency' mentioned. On the other hand it would be correct to say "Change to frequency 134.1" because that isn't an 8.33 channel number. But in practice nobody's likely to be shot down in flames for misusing such terminology.


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Europa48



Joined: 01 Feb 2018
Posts: 28
Location: Kelso

PostPosted: Wed Jul 24, 2019 10:29 pm    Post subject: Re: Frequencies and 8.33 Channel numbers Reply with quote

Hello Jonathan

Does that mean that when taking to a station that is using a 25 KHz frequency you should select 25 KHz mode rather than use 8.33 kHz mode?


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JonathanMilbank



Joined: 14 Apr 2012
Posts: 277
Location: Aberdeen area

PostPosted: Thu Jul 25, 2019 8:18 am    Post subject: Re: Frequencies and 8.33 Channel numbers Reply with quote

Hi Europa48,

The short answer is probably "yes", based only on our local situation where as soon as we leave our airfield 8.33 channel, we must talk to Aberdeen Offshore Radar on frequency 134.1 MHz which is on the original 25 KHz spacing. My Icom radio is quite difficult to switch between 8.33 and 25 KHz modes, causing too much distraction while attempting to do so.

Therefore I have Aberdeen Radar 134.1 MHz permanently in the list of memories, which causes the radio automatically to operate on 25 KHz mode only when accessing a specific 25 KHz memory. If I then choose to turn the two selection knobs for some reason, they resume functioning in 8.33 directly without any input from me.

If I were to change the radio to 25 KHz mode, then the selection knobs would operate in 25 KHz steps, which would be unwise because almost all airfields and airports have gone over to 8.33 channels. The only reason that Aberdeen Offshore remains on 134.1 MHz is because it's Rebro, having 3 additional satellite rebroadcasting stations on such remote locations as offshore platforms. To change all that would be a considerable challenge.

I'm not an expert in this field, but I suggest that you should leave your radio set in 8.33 mode and put any old 25 KHz frequencies into memory.

Experience has clearly shown that talking to Aberdeen Offshore on channel 134.105 instead of frequency 134.1 MHZ gives poorer results and it's also "illegal"!


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groups(at)thegoddards.com
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PostPosted: Thu Jul 25, 2019 11:31 am    Post subject: Frequencies and 8.33 Channel numbers Reply with quote

When set to 8.33 you select channel numbers and not frequency:
Channel 134.100 is 134.1 MHz 25 KHz
Channel 134.105 is 134.1 MHz 8.33 KHz

You do not need to set your radio to 25KHz mode access the original 25KHz frequencies, just dial in the appropriate channel number and it swaps from 25 to 8.33 spacing automatically.

Vince
G-BWUP & G-BJAF
Europa Cub

Sent from my iPad

Quote:
On 25 Jul 2019, at 17:18, JonathanMilbank <jdmilbank(at)yahoo.co.uk> wrote:



Hi Europa48,

The short answer is probably "yes", based only on our local situation where as soon as we leave our airfield 8.33 channel, we must talk to Aberdeen Offshore Radar on frequency 134.1 MHz which is on the original 25 KHz spacing. My Icom radio is quite difficult to switch between 8.33 and 25 KHz modes, causing too much distraction while attempting to do so.

Therefore I have Aberdeen Radar 134.1 MHz permanently in the list of memories, which causes the radio automatically to operate on 25 KHz mode only when accessing a specific memory. If I then choose to turn the two selection knobs for some reason, they resume functioning in 8.33 directly without any input from me.

If I were to change the radio to 25 KHz mode, then the selection knobs would operate in 25 KHz steps, which would be unwise because almost all airfields and airports have gone over to 8.33 channels. The only reason that Aberdeen Offshore remains on 134.1 MHz is because it's Rebro, having 3 additional satellite rebroadcasting stations on such remote locations as offshore platforms. To change all that would be a considerable challenge.

I'm not an expert in this field, but I suggest that you should leave your radio set in 8.33 mode and put any old 25 KHz frequencies into memory.




Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=490529#490529











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Corinthian



Joined: 30 Jan 2018
Posts: 11

PostPosted: Thu Jul 25, 2019 11:40 am    Post subject: Frequencies and 8.33 Channel numbers Reply with quote

Thanks, only how i understood from the previous message was that using 8.33 for 25khz might result in a weaker reception.

David

G-FITY

Quote:
On 25 Jul 2019, at 20:30, Groups <groups(at)thegoddards.com> wrote:



When set to 8.33 you select channel numbers and not frequency:
Channel 134.100 is 134.1 MHz 25 KHz
Channel 134.105 is 134.1 MHz 8.33 KHz

You do not need to set your radio to 25KHz mode access the original 25KHz frequencies, just dial in the appropriate channel number and it swaps from 25 to 8.33 spacing automatically.

Vince
G-BWUP & G-BJAF
Europa Cub

Sent from my iPad

> On 25 Jul 2019, at 17:18, JonathanMilbank <jdmilbank(at)yahoo.co.uk> wrote:
>
>
>
> Hi Europa48,
>
> The short answer is probably "yes", based only on our local situation where as soon as we leave our airfield 8.33 channel, we must talk to Aberdeen Offshore Radar on frequency 134.1 MHz which is on the original 25 KHz spacing. My Icom radio is quite difficult to switch between 8.33 and 25 KHz modes, causing too much distraction while attempting to do so.
>
> Therefore I have Aberdeen Radar 134.1 MHz permanently in the list of memories, which causes the radio automatically to operate on 25 KHz mode only when accessing a specific memory. If I then choose to turn the two selection knobs for some reason, they resume functioning in 8.33 directly without any input from me.
>
> If I were to change the radio to 25 KHz mode, then the selection knobs would operate in 25 KHz steps, which would be unwise because almost all airfields and airports have gone over to 8.33 channels. The only reason that Aberdeen Offshore remains on 134.1 MHz is because it's Rebro, having 3 additional satellite rebroadcasting stations on such remote locations as offshore platforms. To change all that would be a considerable challenge.
>
> I'm not an expert in this field, but I suggest that you should leave your radio set in 8.33 mode and put any old 25 KHz frequencies into memory.
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=490529#490529
>
>
>
>
>
>
>
>
>








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Burrilla



Joined: 25 Apr 2015
Posts: 115

PostPosted: Thu Jul 25, 2019 12:02 pm    Post subject: Frequencies and 8.33 Channel numbers Reply with quote

Ok if you have a radio, let’s say a Garmin, and you set it to 8.33 mode then when you select an 833 channel the appropriate frequency and bandwidth is selected. If you step though the channels/frequencies it will also allow selection of an 25khz frequency and the radio will automatically select the 25khz frequency and bandwidth to suit. You do not have to go into the menu system to set it back to the 25KHz mode.

There will be no difference in quality as speech is confined to 300 to 3KHz regardless which is well within the 8.33 bandwidth. I’m sorry those who claim there is a difference in speech quality or signal strength are misleading or possible have been using poorly maintained radios.

There is an issue with ICAO radios in that their first attempt at an 833 radio resulted in it not been able to select 25 KHz frequencies when configured in the 8.33 mode so you could not for example select 121.5, which will remain a 25KHz frequency for technical reasons. There is however a firmware upgrade available, free I believe, which fixes this problem and then allows you to step through 833 and 25KHz channels and frequencies as appropriate without switching between the two operating modes, or setting them up in the memory which is a workaround.

The radio takes care of the appropriate tuning of the circuits to suit.

Alan Burrill

Sent from my iPad

Quote:
On 25 Jul 2019, at 20:40, David Lewendon <davidlewendon(at)me.com> wrote:



Thanks, only how i understood from the previous message was that using 8.33 for 25khz might result in a weaker reception.

David

G-FITY

> On 25 Jul 2019, at 20:30, Groups <groups(at)thegoddards.com> wrote:
>
>
>
> When set to 8.33 you select channel numbers and not frequency:
> Channel 134.100 is 134.1 MHz 25 KHz
> Channel 134.105 is 134.1 MHz 8.33 KHz
>
> You do not need to set your radio to 25KHz mode access the original 25KHz frequencies, just dial in the appropriate channel number and it swaps from 25 to 8.33 spacing automatically.
>
> Vince
> G-BWUP & G-BJAF
> Europa Cub
>
> Sent from my iPad
>
>> On 25 Jul 2019, at 17:18, JonathanMilbank <jdmilbank(at)yahoo.co.uk> wrote:
>>
>>
>>
>> Hi Europa48,
>>
>> The short answer is probably "yes", based only on our local situation where as soon as we leave our airfield 8.33 channel, we must talk to Aberdeen Offshore Radar on frequency 134.1 MHz which is on the original 25 KHz spacing. My Icom radio is quite difficult to switch between 8.33 and 25 KHz modes, causing too much distraction while attempting to do so.
>>
>> Therefore I have Aberdeen Radar 134.1 MHz permanently in the list of memories, which causes the radio automatically to operate on 25 KHz mode only when accessing a specific memory. If I then choose to turn the two selection knobs for some reason, they resume functioning in 8.33 directly without any input from me.
>>
>> If I were to change the radio to 25 KHz mode, then the selection knobs would operate in 25 KHz steps, which would be unwise because almost all airfields and airports have gone over to 8.33 channels. The only reason that Aberdeen Offshore remains on 134.1 MHz is because it's Rebro, having 3 additional satellite rebroadcasting stations on such remote locations as offshore platforms. To change all that would be a considerable challenge.
>>
>> I'm not an expert in this field, but I suggest that you should leave your radio set in 8.33 mode and put any old 25 KHz frequencies into memory.
>>
>>
>>
>>
>> Read this topic online here:
>>
>> http://forums.matronics.com/viewtopic.php?p=490529#490529
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
>
>
>
>
>







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JonathanMilbank



Joined: 14 Apr 2012
Posts: 277
Location: Aberdeen area

PostPosted: Fri Jul 26, 2019 4:15 am    Post subject: Re: Frequencies and 8.33 Channel numbers Reply with quote

My Icom radio is new and has had a free upgrade. My aircraft is shared with others and there is no doubt at all that when flying in a certain direction at the same altitude, we experience poorer comms with channel 134.105 than with frequency 134.1 KHz. For one thing, the range at which comms are possible is noticeably less. That might be an issue with Icom radios only, but it's real and repeatable.

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Kelvin Weston



Joined: 14 Apr 2010
Posts: 70
Location: Hampshire, UK

PostPosted: Sat Jul 27, 2019 1:24 am    Post subject: Re: Frequencies and 8.33 Channel numbers Reply with quote

Hi Jonathan

Most low-end GA radios require you to select either 8.33 or 25Khz mode in the setup and will only display the associated channels or frequencies for that bandwidth.
If you have a radio that allows you to select both channels and frequencies directly using the frequency select knob, then it may well adjust the bandwidth automatically.
Whichever mode you are in, selecting a frequency of 134.1 in 25 Khz mode or channel 134.105 in 8.33 mode will use the same carrier frequency of 134.1 Mhz for transmit and receive.
However due to the differing bandwidths, a 25 Khz station should be able to receive your transmission ok but an 8.33 station (your aircraft) may not receive a 25 Khz transmission as clearly.
This can be due to a number of factors concerning radio wave propagation, transmission, etc. and is a known issue. See the 2nd to last paragraph of this article issued by Eurocontrol:
https://833radio.com/news/show/7
There are lots of similar articles on the web.
Unless you wish to change radio, your current method is probably the best way to achieve satisfactory comms with regularly used 25 Khz stations.


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_________________
Regards

Kelv Weston
Kit 497
kelv@kdweston.biz
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JonathanMilbank



Joined: 14 Apr 2012
Posts: 277
Location: Aberdeen area

PostPosted: Sat Jul 27, 2019 8:02 am    Post subject: Re: Frequencies and 8.33 Channel numbers Reply with quote

Thanks Kelvin. An interesting article.

Another factor re Aberdeen Offshore Radar 134.1 MHz occurs to me, viz some years before the introduction of 8.33 KHz channel spacings, Aberdeen had already introduced rebro for offshore helicopter communication purposes and thus three additional remote transmitters were placed on offshore platforms over 100 miles apart. This also involved telephone links to the remote transmitters and synchronisation problems were challenging.

From what I think I was told, the 25 KHz band segment assigned to 134.1 MHz was subdivided into 4 of about 6 KHz each (I guess) and so the transmissions had very narrow bandwidth but the receivers remained capable of the full 25 KHz. At least this is what I vaguely recall from my days of flying helicopters to North Sea destinations. There were "black holes" in the coverage offshore.

I wonder if the difference between 8.33 KHz bandwidth of my aircraft radio and the presumed 6.25 KHz of the rebro system causes some "mismatching" effects, when my radio is erroneously selected to channel 134.105? Any polite suggestions welcome!


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