Seem to remember reading that LUF is a calculation based on D layer
absorbtion. Propagation predictions software giving LUF uses sunspot
number / solar flux and time plus lat / long, but unlike MUF, also needs
transmitter and antenna properties in order to calculate signal strength
LUF is the lowest frequency that will propagate over the skywave path(s)
that is subject to the D layer absorbtion, whereas MUF is a geometrical
consideration only, so doesn't need power and antenna details.
From: Mike Dennison [mailto:[email protected]]
Sent: 2001-05-17 12:07
To: [email protected]
Subject: Re: LF: Re: LF Prop.
> There is this thing called LUF (Lowest Usable Frequency).
Not much in ham
> literature about it but from Bill Orr's Radio Handbook it depends on
> transmitter erp and atmospheric noise. Generally speaking
the LUF can be
> lowered (at HF) by approximately 2MHz for each 10dB increase in erp.
> However it is obvious that the LUF changes throughout the
day. Does it
> follow the MUF? If it does then it will follow the sunspot cycle.
> Are there any average graphs of LUF?
My understanding is that LUF and MUF are purely F-layer
functions, so are
not relevant to us if you accept Alan's assumption that
is by D-layer with perhaps some E-layer. Also, is the MUF
really measured? It
will change for every path, and for prediction purposes is
from the Critical Frequency (ie the point at which the
signals go straight
through the ionosphere). Perhaps LUF is also just a calculation.
Mike, G3XDV (IO91VT)
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