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LF: RE: LF Prop.

To: [email protected]
Subject: LF: RE: LF Prop.
From: "Talbot Andrew" <[email protected]>
Date: Thu, 17 May 2001 13:17:09 +0100
Reply-to: [email protected]
Sender: <[email protected]>
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.

Andy  G4JNT

-----Original Message-----
From: Mike Dennison [mailto:[email protected]]
Sent: 2001-05-17 12:07
To: [email protected]
Subject: Re: LF: Re: LF Prop.

G3LDO wrote:
> 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 sky-wave propagation 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 usually calculated 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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