Transceivers and 8.33kHz spacing

[BayAreaLondoner]

I am in the US and I have an Icom A4 transceiver. Quite nice and does the job but has a crappy way of selecting frequencies (up/down only, no direct entry keypad).
Anyway, I'm contemplating getting rid of this one and getting one that does have a keyboard. At the same time, I will be moving back to Europe sometime in the next two years.
Now, all the handheld transceivers I've seen with the exception of the Sporty's one (which is massive) do 25kHz spacing. Is 8.33kHz spacing a reality for GA pilots in Europe or does it affect commercial operators more?

[IFollowRoads]

Its only effective over here at above FL195 (or something like that - higher that a non-turbo Arrer goes)

[BayAreaLondoner]

Thanks IFR!
Little chance of my getting that high in my spam-can.
Any rumours of that spacing affecting lower altitude drivers?

[Keef]

I've not checked the official website for a few weeks, but the declared intention of bureaucratdom is to extend 8.33 kHz spacing to all of Europe and all levels.

So in 10 years' time you might need a handheld with the facility.

Probably in France first.

BUT ... last time I looked, there was still some debate about how to "name" the other frequencies. It might not be "123.99167" but end up something like "123.987Y" rather like TACAN channels. Really confusing.

[BayAreaLondoner]

Thanks Reef.
Looks like I'll be buying one with 25kHz spacing then.

[A and C]

the 8.33 spacing works just like the normal radio except that when the controler tells you to change he should say "contact XYZ radar on CHANNEL 132.015"

In this case the ACTUAL frequency that you will be transmiting on would be 132.0167 but 132.015 is what you will select on the radio box .

The system is all up and running above FL195.

[Keef]

A & C - good news! So they settled for the "call it channel and use the nearest 5 kHz" option. Hadn't heard that that is the final answer, but it's probably the best one.

I'm still bemused at the choice of 8.33kHz, but I suppose that's committees for you!

[Tinstaafl]

8.33 is 1/3 the current .25MHz frequency division.

It gives 3 communication channels instead of only two if previous methods of just halving the current frequency division had been used

[Keef]

I'd sort-of sussed the arithmetic. My confusion was "why not go for 5kHz channel spacing" which would have been simpler in many ways.

After all, if the receiver can't handle signals 5 kHz away, it's not going to do a lot better with signals 8.33 away.

But never mind. Their Lordships have done what they've done.

[slim_slag]

After all, if the receiver can't handle signals 5 kHz away, it's not going to do a lot better with signals 8.33 away.

The limiting factor is only not the receiver, or the transmitter. It's the fact that its still AM, and you also need to accept the fact that radios may not be tuned 100%.

Acceptable frequency error of receiver may only be around 0.003%, but if you are transmitting in the 120Mhz range that is approx 3 to 4 kHz.

The transmitter has the same error, which is another 3 to 4 kHz.

AM means you get sidebands on either side of the transmitter signal, and if your carrier wave is 2kHz, then you have 4kHz.

Add them all together, and you have busted 8kHz quite nicely.

And that is from my basic knowledge. I know Jack about radio design, but I have spoken with "experts" who think you need at least 17kHz spacing due to bleed through, and 20kHz is a nice minimum - if you use AM.

Other Authorities have not gone for 8.33kHz spacing, and for good reason. If you are going to change your radios, you may as well go digital. Lets hope that when the US goes that way, European GA owners are not forced to follow suit at further expense.

[Keef]

All valid, slim_slag.

With accurate synthesisers, and sharp passbands, an AM receiver can be set up to 5kHz bandwidth and work just fine.

Clearly, if the transmitter or receiver is "off", then there will be problems - but most commercial synthesised kit is aligned precisely and tends to stay where it's put. My HF gear here can "find" a frequency to within 50 Hertz at frequencies up to 50MHz. It does have to be checked against a known standard from time to time. That's SSB, and uses 3kHz bandwidth.

I think the point of narrow channelling is that the adjacent frequencies wouldn't be used by stations close together. With the right planning/modelling process, 5 kHz channelling would have been more flexible than 8.33 - it all depends on the stability/accuracy standards applied.

BUT ... present-day aircraft VHF receivers aren't anything like as "sharp" as 5 kHz bandwidth anyway. Some "multiple output" stations (I think Volmet is one, and London Info another) have base stations in several places, all on the same "nominal" frequency but actually far enough apart in frequency that you don't hear a heterodyne from them: just the strongest one wherever you happen to be.

Fascinating topic if you're into that sort of thing. Sad, if you're not.