Yup, I made a typo when I said "F" layer in relation to Terman's
discussion of the E layer, - probably because I intended to discuss the
F layer...

But, I bring us back to the topic, no where do I see HF mentioned in
the quotes from Terman... Ground wave transmission becomes markedly
poorer beginning somewhere around a thousand KC - which is why hams
were relegated to the waste land of 200 meters and down....

BTW, here is an interesting discussion of the D and E layers for VLF
propgation...
http://www.aavso.org/observing/progr.../vlfprop.shtml

But to bring us back to the major complaint which seems to be that the
Nec engine doesn't model the last few degrees over ground very well, so
that the zero angle is discarded by the software... Richard seems on a
mission to prove the NEC engine wrong - well, I agree, the NEC engine
does have limitations for low angle signals which is why the authors
have installed an angle cut off... Per Richard's citations, Terman's
data proves that for MW signals - but not for HF ( a different kettle
of fish)...

If we look at the ham antenna literature over the 50 years predating
the advent of the NEC engine, we do not see much championing of the 5/8
wave vertical for lower HF... Since these folks did not have the NEC
engine poisoning their thinking one has to ask why the lack of
interest... The explanation for that, in my mind, is because it does
not have significant propagation advantage at HF offsetting it's
greater mechanical and financial burden to install... And because the
high angle lobes that are beginning to bulge are disadvantageous with
an antenna that is intended for low angle receiving/transmitting...

In my case I have a 4/8 wave vertical for 80 meter sitting on an
elevated base... Extending it to 5/8 wave would be a trivial task -
but I see no advantage to doing so...

denny / k8do