The high pressure in the UK over the past week has caused some surprises. When using a 25kHz frequency, I heard some French voices on the radio, breakthrough from some distant airfield elsewhere.
Now that 8.33 is widely implemented throughout Europe, have other pilots found breakthrough remains a problem or not?
It should be one of the few benefits we can expect.
The ELLX ATIS recently switched to 8.33kHz, from 134.750 to 134.755, so without actually changing the frequency. At around Brussels, I actually hear Langen (or was it Frankfurt?) breakthrough! It never happened to me before the switch. Very weird.
Actually, transmitting the same power on a reduced bandwidth make the signal readable farther.
So more range but more interference on the same frequency 
The transmitter bandwidth is the same on an 8.33k channel as on a 25k channel – because with AM (amplitude modulation) the carrier deviation is simply the incoming audio, deviating either side of the centre frequency.
So with e.g. a 2kHz audio signal a 125MHz carrier will be presented as two peaks in the spectrum; one at 124.998MHz and the other at 125.002MHz.
And with e.g. audio varying from 0 to 2kHz (let’s disregard that it cannot go down to 0) a 125MHz carrier will be swinging from 124.998MHz to 125.002MHz.
So I cannot see how a transmission on an 8.33 channel can reach further, given the same receiver sensitivity.
One often hears French voices in the UK.
Same power on high frequency bandwidth should go further but that has nothing to do with 8/25 spacings if the modulation frequency stays the same (I am referring to the A/F modulation frequency not the orginal frequency of the naked audio signal wich is in 2Khz range)
The high pressure is also irrelevant we are talking about electromagnitic waves that propagates with the same “universall properties” even in vacum, unless the high pressure pushes the ionosphere higher I don’t see how it has an impact? difference in RT reception due to night/terrain/water relates to different matters…
So unless the French changed their frequency allocation after 8.33 transition for few signals to reach UK on your specification location, but honestly the difference in range from 136MHz and 118Mhz modulations is really low around 8%, the only plausible scenario is the following a French field is far by 88nm from you was on 118MHZ/25 frequency you could not hear (say range is 80nm) it but now you hear it on new 136MHZ/8.33 frequency, the frequency change was done along the same time as the 8.33 reshuffle? The other explanation is someone finally got 8.33 equipement to be able to speak while complying with the rules so he lets everybody know about it :)
Ibra wrote:
The high pressure is also irrelevant we are talking about electromagnitic waves that propagates with the same “universall properties” even in vacum, unless the high pressure pushes the ionosphere higher I don’t see how it has an impact?
I believe the phenomena is called duct propagation.
Yes, pronounced temperature inversions may give the same effect as the skywave in high atmosphere by night but I doubt the magnitude on VHF is really that high? It should be along what we see in RT transmission from other weather effects due to water, snow, rain and storms
Of course the impact depends on the range of wavelengths, a temperature inversion will have a pronounced impact on high frequencies like UHF/Radar in GHZs or on visibility/light in THZs than in the VHF range…
The Stansted ILS seems to dominate the Bournemouth ILS08 in the descent over Southampton on days with a strong inversion. The ILS doesn’t auto ident or auto slew until you are on base RV, while the Stansted autoident shows pretty well all the way to Bournemouth.
Yes, this Spring we see the feared increase in radio congestion. All these guys changing from old 25 radios on 3-5 watts to 833 radios on 10-16 watts now blow the sky from North Cape to Gibraltar in one transmission. Add a little radio inversion, like last weekend, and you hear traffic pattern communication from never thought before. Mixing 25 and 833 does not make things better and I suspect the net effect of 833 is Nil. I wonder why they did not put a mandatory low power mode on the 833 radios for traffic pattern and formation Com’s?
