alioth wrote:
The medium does affect electromagnetic waves and significantly. The earth’s atmosphere is almost opaque to some RF frequencies for instance.
I am wrong on that, I am referring to RT wavelength segments 
You may get pronounced impact from air+water medium on high frequencies in GHZ bands (liquid water resonates to radar) and in THZ bands (vapour water resonates to light) but within a line-of-sight you will have very small effect on VHF/UHF from weather (e.g. snow, night duct, storms, sun) tough VHF/UHF may or may not reach space or a point on earth due to atmospheric conditions outside a line-of-sight
We rarely account for weather effects on RT while planning but we know we will have zero viability in fog as water resonates to light 
I doubt what happens in ionosphere by day/night can be called “weather” but temperature inversions at 5000ft are probably more relevant
Ibra wrote:
The high pressure is also irrelevant we are talking about electromagnitic waves that propagates with the same “universall properties” even in vacum
The medium does affect electromagnetic waves and significantly. The earth’s atmosphere is almost opaque to some RF frequencies for instance.
You can get surprising VHF propagation. Sporadic E propagation can make a low power VHF transmission go thousands of kilometers, but it’s generally pretty short lived (sporadic E is to do with the E layer of the ionosphere). You can also get tropospheric ducting which can make VHF/UHF transmissions go a long way beyond line of sight (thousands of km). Aircraft propagation is also something that can happen in the VHF/UHF bands – radio amateurs often bounce signals off airliners to make VHF DX contacts on the 2m and 70cm bands.
From Wikipedia’s page on radio propagation:
“Sudden changes in the atmosphere’s vertical moisture content and temperature profiles can on random occasions make UHF, VHF and microwave signals propagate hundreds of kilometers up to about 2,000 kilometers (1,200 miles)—and for ducting mode even farther—beyond the normal radio-horizon. The inversion layer is mostly observed over high pressure regions, but there are several tropospheric weather conditions which create these randomly occurring propagation modes. Inversion layer’s altitude for non-ducting is typically found between 100 and 1,000 meters (330 and 3,280 feet) and for ducting about 500 to 3,000 meters (1,600 to 9,800 feet), and the duration of the events are typically from several hours up to several days. Higher frequencies experience the most dramatic increase of signal strengths, while on low-VHF and HF the effect is negligible. Propagation path attenuation may be below free-space loss. Some of the lesser inversion types related to warm ground and cooler air moisture content occur regularly at certain times of the year and time of day. A typical example could be the late summer, early morning tropospheric enhancements that bring in signals from distances up to few hundred kilometers for a couple of hours, until undone by the Sun’s warming effect.”
In my case it was the direct comparision- I was crawling at 1000ft to stay under the cloud layer from Latvia to Estonia, at the border Riga CTR told me to contact Tartu (ca 80km from the border). Radio A(old) – no response, new one loud and clear..
I think there are lot of factors that have changed with 8.33 upgrades than just the 25Khz/8.33Khz spacing: power (6W to 16W), squelch (0 to 10), volume (0% to 100%) and wiring/interference/antenna being the main ones…I get different RT reception in the same radio models let alone when receiving using a fresh new model, also TX stations may had recent changes of their hardware that has nothing to do with your upgrade that explains why they may not reply back
from ca 20km farther than on the old unit.. But this is probably due to better antenna/cabling.
I have never seen a KX125
However in any case 6W to 10W isn’t going to produce a significant range extension. I make it just 29%, and that is the very best case as it assumes line of sight, which often in GA (flying at low level, and thus comms with a ground station often being terrain limited) is not the limiting factor.
Your earlier post “on 3-5 watts to … 10-16 watts” would produce more, but are there any 3W (panel mount) radios? The GNS430 is 10W, like most/all the King radios, and had an “A” version (16W) which almost nobody had. The IFD540 is also 10W, with a 16W option.
Going 3W to 16W would produce a 2.3x increase in line of sight range but I would suggest this is an extremely rare scenario in the GA population.
Peter wrote:
Can you give examples of actual radios?
I.e. popular update: from KX125 (6W) to TY96 or TY56 (10W), almost everybody I know took the change to increase TX power, very few exceptions.
In the UK, I got this from the NATS website that summarize UK chart frequencies, very handy when SD goes off
There is probably one from DGAC?
If the reception is good, then with good English/French ear, you could guess the place ;)
All these guys changing from old 25 radios on 3-5 watts to 833 radios on 10-16 watts
Can you give examples of actual radios?
You can do a search on the channel (old, frequency) in several moving map applications.
There have “always” been websites which list aero frequencies and who they belong to. There is a big crowd of “frequency spotters” out there. How current they are, I don’t know…
Capitaine wrote:
Is there a way to find who uses a particular frequency?
That really was a mess before the age of EFBs and databases in navigation programs.
You can do a search on the channel (old, frequency) in several moving map applications.
