This also means that if you are assigned 130.005 130.030 130.080 i.e. any of the 25kHz frequencies plus 5, you can tune in 130.000 etc on a 25kHz radio and nobody will know any difference 
So if any station gets a .005 frequency, it doesn’t really mean anything. This is useful to know if you have one 8.33 radio and one 25 radio and want to make full use of both. Or you are flying some simple plane with just a 25k radio, or a vintage type with a handheld radio.
Peter wrote:
or a vintage type with a handheld radio
It never crossed my mind that I may have to upgrade (i.e. throw away) my handheld radio as well, which I keep as a backup. It comes in handy in some “vintage types” where the built-in radio is so poor that I prefer to use the handheld.
Peter wrote:
So if any station gets a .005 frequency, it doesn’t really mean anything.
Of course it means something. It means that another station in range could have a .010 channel and interfere with your reception on the .005 channel.
Airborne_Again wrote:
Of course it means something. It means that another station in range could have a .010 channel and interfere with your reception on the .005 channel.
In principle, yes, but unlikely in practice. In fact, even 25 kHz-spaced frequencies were usually allocated so as to avoid having two adjacent channels used in the same area.
An interesting Q is why this +5 “fake frequency” bodge was done.
It looks like it was deemed necessary to get around the old transmitter spec which allows the carrier to be some kHz off, which resulted in a wide receiver spec. That spec has to be very old because even 8kHz is 80ppm off, but even a really crappy crystal, €0.10, is 20ppm (i.e. 2kHz off) and nobody would have used such a crappy part even in 1970. I had a job in 1973 where they used 5ppm crystals (£1) and put them inside a +90C oven (£10). I can’t find a pic now but this is the sort of thing but was a lot smaller. None of this is even slightly relevant on the scale of avionics costs. And in the 1980s you had miniature temp-compensated oscillators, 1ppm (100Hz) accurate, costing peanuts.
unlikely in practice
Yes, and anyway intereference is a risk only when somebody is actually transmitting. In reality the powers to be know a load of old gear will not be retired so they will avoid such frequency allocation (if they are smart).
AFAIK they originally thought offset carrier operation on 8.33 was unfeasible. It is however desirable for covering large areas, providing redundancy and covering areas with challenging terrain. AFAIK UK utilizes this by far the most, I think more than the rest of EU combined. Later research showed they could do ±2.5 kHz IIRC (allowing only for two-legged climax). On 25 kHz spaced channels, IIRC ±2.5, ±5 and ±7.5 can be used depending on the number of legs. I don’t think they specified ±8 kHz because of crappy crystals. And Airborne_Again wrote that the Annex 10 calls for ±0.003 % for 25 kHz spacing.
Martin wrote:
Let’s stick with 130.000. If it’s a 25 kHz spacing assignment, the designator will be 130.000. That’s what you’ll see on the radio and on your charts. However, if it’s a 8.33 assignment, the same frequency would be designated as 130.005. So it’s:130.000 – 130.000 MHz with 25 kHz spacing
130.005 – 130.000 MHz with 8.33 kHz spacing
130.010 – 130.008 MHz with 8.33 kHz spacing
130.015 – 130.017 MHz with 8.33 kHz spacing
130.025 – 130.025 MHz with 25 kHz spacingYou shouldn’t be experiencing interference because 130.010 shouldn’t be assigned as long as 130.000 is assigned. They create 8.33 kHz frequency assignments by decommissioning 25 kHz frequency assignments. That’s how I understand it.
This is the kind of thing that only the EU bureaucracy could invent. Instead of having a dead easy and straight forward system with :
130.000
130.008
130.017
130.025
They make this counter intuitive nonsense. And for what? If you have a 8.33 radio, you will always have 8.33 “spacing”. In 2018 everybody must have 8.33 radio anyway, the “spacing” will be irrelevant.
The +.005 is a fake frequency setting, which just tells the radio to tighten up the receiver bandwidth.
It took me a while to get my head around this stunt…
Yes, but to what purpose does it serve? Within a couple of years all will be 8.33 and we are left with two frequencies (channels) with the same frequency. I just don’t get it.
@LeSving, for flights outside the 8.33 area.
