OH1TV   OH1O   OH1WX
	Critical frequency foF2-limited local QSO on 7MHz
		When F2 layer height = 250km
		Ionogram	Shortest			Corresponds to 3000km
		foF2	distance	TOA		MUF	TOA
		2.0	2540	5.2		7.3	2.5
		2.5	1560	13.9		9.1	2.5
		3.0	1170	20.1		10.9	2.5
		3.5	925	25.8		12.7	2.5
		4.0	750	31.5		14.5	2.5
		4.5	613	37.3		16.3	2.5
		5.0	500	43.3		18.2	2.5
		5.5	398	50.0		20.0	2.5				TOA = antenna take off angle
		6.0	303	57.6		21.8	2.5
		6.5	200	67.4		23.6	2.5				Critical frequency foF2 link
		6.8	121	75.9		24.7	2.5
		6.95	60	82.9		25.2	2.5
		7.0	0	90.0		25.4	2.5
		MHz	km	deg		MHz	deg
		Observations:
		Band is closed when foF2 is less than 2MHz
		Very short ,few tens of kilometers, QSO via F2 is possible when foF2 is 7MHz or more
		QSO down to 500km is possible via F2  when foF2 is 5MHz, etc
		QSO may still be possible via other propagation modes like back scatter, F1 etc.
		Back											28.4.2012