Are you wondering why you rarely hear MX0PHX on the air - in the UK - on 40m?
In the conditions now prevailing it is very rare for the 7MHz skip distance to be less than 400km. Naturally, contacts may still be possible over longer distances.
This map (below left) shows various circles (in km) from IO92KT where MX0PHX is located, although 'skip zones' are rarely true circles. However, it is clear that if the observed foF2 critical frequency will only support reliable 40m band contacts at distances much greater than 200km MX0PHX will not normally be heard. Equally, with a 400km skip zone (a regular situation) MX0PHX will normally only be able to hear UK stations in Scotland, Cornwall, Northern Ireland an Europe. An example ionogram, showing skip distances is given below. The circles on the map are only a guide to distances, in reality 'skip zones' may have a much more irregular and asymmetrical 'shape'.
For comparison, MX0YHA - Youth Hostels ARG - located near Skipton in N. Yorkshire is 150km north of MX0PHX which means that when the skip distance is c.200km on the 40m band much more of England is within range for reasonably reliable contacts.
This map shows the approximate areas which fall within a 200km 'skip zone' centred on the locations of MX0PHX (Nottingham) and MX0YHA (near Skipton). In reality, 'skip zones' are not circular, so the diagram is just a simple guide to distances from each station. It is evident that MX0PHX will have greater difficulty making contacts in southern England than MX0YHA: the same is true for contacts between MX0YHA and stations farther north.
The calculated Maximum Usable Frequencies for distances of 100 to 3000km are shown at the bottom. In this example, at a working frequency of 7.100MHz, the skip distance will be around 600km, giving poor (or near impossible) two-way communications across the UK (at least, for MX0PHX).
Conditions (critical frequency, MUF and skip distance) will not be exactly the same in another part of the UK more distant from Fairford - such as northern Scotland - but MX0PHX is located close enough to Fairford and Chilton/Harwell (200km) for foF2 conditions and skip distances to be similar.
It is not currently possible to find ionograms from northern Britain online, so some extrapolation is needed if you are significantly more than 200km from Chilton/Harwell or Fairford (see the Propagation page)