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Latest on 8.33 requirements (merged)

True, but a different argument

Certainly the 8.33 business will remove a lot of old radios from GA.

Administrator
Shoreham EGKA, United Kingdom

Thanks Peter!

ESOW Västerås, Sweden

What an interesting discussion here. I’ll dig that out again because I’d be interested in the following. As stated by others there are lots of frequencies which correspond to “old” 25 kHz frequencies plus 5 kHz. So an arbitrary 130.625 is now 130.630.

And I’m really surprised to see, now that I understood this, that there seem to be in fact the majority of frequencies in Europe still those 25 kHz ones.

As far as I understood, tuning in a “+5” frequency like 130.630 into a 8.33 kHz radio tells the radio to use in fact 130.625 but to narrow down the bandwidth. Is that correct?

But…what would happen if I tune in 130.625 (to stay in that example) on a 25 kHz radio? Regarding listening? And regarding transmitting?

As far as I understand listening should be possible without any degradation. This is of particular interest, e.g., for using an old com to listen to ATIS or any MET transmission. But what is with transmitting, would this be receivable?

Germany

UdoR wrote:

As far as I understand listening should be possible without any degradation. This is of particular interest, e.g., for using an old com to listen to ATIS or any MET transmission. But what is with transmitting, would this be receivable?

yes, no probllem listening to .130 ATIS on .25 radio, also possible to talkk to 8.33 radio.

EETU, Estonia

Whoa! Will try this! This would solve some problems for me (in particular: to have a free device to be able to read ATIS or any other frequency of interest during flight). Thank you for the quick reply!

Last Edited by UdoR at 16 May 13:06
Germany

tuning in a “+5” frequency like 130.630 into a 8.33 kHz radio tells the radio to use in fact 130.625 but to narrow down the bandwidth. Is that correct?

Yes, and only the receiver bandwidth gets tightened (to reduce chances of adjacent channel interference). The transmitter bw is still the same; the way AM (amplitude modulation) works is that the carrier wobbles up and down by the same amount as the modulating (the audio) signal, so not a lot one could do about that.

Basically any “25k + 5k” channel works as before.

Only the “genuine 8.33” channels probably won’t – for either TX or RX. So say 130.010 (which is actually 130.00833333333…) cannot be usefully accessed on a 25k radio, because 130.000 is too far away and 130.025 is also too far away.

I don’t know why this “fake +5k” was done; a discussion is further back in the thread. Probably because it makes the user interface simple, because how would you publish 130.0083333…? As to why most channels published as 8.33 are actually 25k channels, well, my guess is that it was done because “they knew” a lot of people won’t be upgrading their radios

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

I don’t know why this “fake +5k” was done; a discussion is further back in the thread. Probably because it makes the user interface simple, because how would you publish 130.0083333…? As to why most channels published as 8.33 are actually 25k channels, well, my guess is that it was done because “they knew” a lot of people won’t be upgrading their radios

A way of differencing between a 8.33kHZ and 25 kHz channel is needed.

You might have 1 ATC of airfield A on 130.630 (8.333kHz channel with a frequency of 130.625 MHz) and an adjacent airfield B on 130.635 (8.33kHz on 130.6333 MHz). In that case you want to listen to only the ATC of airfield A so you need the narrow receiver bandwidth.

You might have a FIS sector with a 25kHz channel of 130.625 MHz. The nominal frequency is 130.625MHz but to cover the whole area, they have 2 transmiters: one on 130.620 MHz and one on 130.630 MHz (no idea of the actual freq, just for example). The frequencies are far away enough that you don’t get distortion if you receive both but you need the wide 25kHz bandwith filter on the receiver to receive any.

Nympsfield, United Kingdom

Peter wrote:

“they knew” a lot of people won’t be upgrading their radios

Well obviously the 8.33 radio is obligatory. However, I have an old mobile radio and could use it to listen to ATIS, where as far as I’ve seen in approach charts all frequencies would have been readable with the old one. I just did not try, because I didn’t know the “5 kHz” trick.

Germany

Xtophe wrote:

You might have a FIS sector with a 25kHz channel of 130.625 MHz. The nominal frequency is 130.625MHz but to cover the whole area, they have 2 transmiters: one on 130.620 MHz and one on 130.630 MHz (no idea of the actual freq, just for example). The frequencies are far away enough that you don’t get distortion if you receive both but you need the wide 25kHz bandwith filter on the receiver to receive any.

Exactly! This is likely the reason why a lot of not only FIS, but also enroute ATC frequencies in Germany are 25 kHz frequencies.

ESKC (Uppsala/Sundbro), Sweden

Peter wrote:

It all works perfectly. The transmission on 125.030 is exactly identical to one on 125.025. The 0.005 add-on merely tell the receiver in an 8.33 radio to select a tighter selectivity.

Before I try it out myself I don’t want to disturb no one. Do I understand it right that any submission (TRANSMIT) from a radio is technically the same be it a 25 kHz radio sending on 125.025 or be it an 8.33 kHz radio sending on 125.030?

Germany
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