[Propagation] Fwd: VOACAP Digest, Vol 5, Issue 2

["NW7US, Tomas" <nw7us@hfradio.org>]

Propagation Members:

The following is an interesting bit of information regarding the VOACAP  
engine.  This is forwarded from the VOACAP reflector.

------- Forwarded message -------
From: voacap-request@mailman.qth.net
To: voacap@mailman.qth.net
Subject:  Sat, 16 Oct 2004 04:03:04 -0400 (EDT)

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Today's Topics:

   1. VOACAP WARNING! (George Lane)
   2. Re: VOACAP WARNING! (George Lane)


----------------------------------------------------------------------

Message: 1
Date: Fri, 15 Oct 2004 15:34:56 -0400
From: George Lane <glane@erols.com>
Subject: [VOACAP] VOACAP WARNING!
To: VOACAP <voacap@mailman.qth.net>
Message-ID: <41702660.7040206@erols.com>
Content-Type: text/plain; charset=us-ascii; format=flowed

Heads UP

In the process of comparing  soundings over 22 days on a circuit, I have
been making correlations studies of the predicted FOT, MUF and HPF
between predictions using VOACAP, ICEPAC and REC 533.  An unexpected
result of this is that I found a strange discrepency in VOACAP when
using Method 9 and Method 26.  The predictions for these values do not
agree but are supposed to be exactly the same.  I checked using ICEPAC
using Methods 9 and 26 and those predictions agree exactly and with
those from VOACAP Method 9.

The correlation coefficient ( R squared) for the Method 9 in VOACAP and
in ICEPAC Method 9 or 26 is 86% for the measured MUF.  But the R^2 drops
to 72% when using the predicted MUF values using VOACAP Method 26.

At this point in time, I feel that VOACAP Method 26 should not be used.
VOACAP Method 9 and ICEPAC Methods 9 and 26 agree and seem to give the
best agreement with measurements.  Rec. 533 seems to have a different
model and gives inferior predictions of the FOT-MUF-HPF at least for
this one set of measured data (10,560 frequency-hour sample points).

George Lane

Lane Consultant


------------------------------

Message: 2
Date: Fri, 15 Oct 2004 17:06:25 -0400
From: George Lane <glane@erols.com>
Subject: Re: [VOACAP] VOACAP WARNING!
To: VOACAP <voacap@mailman.qth.net>
Message-ID: <41703BD1.6040100@erols.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed


Stand by:

It seems I was using two different minimum angles in VOACAP (i.e. 3.5
deg. and 3.0) which was making the big differences between the
FOT-MUF-HPF predictions between Method 9 and Method 26.  When the
minimum angles are the same the same they agree totally.  Method 5
(nomograph method) is different as would be expected.

The remaining question is why do ICEPAC and VOACAP have such different
predictions when Qe is set to 0 in ICEPAC.  Right now it appears that
ICEPAC is giving better predictions for the FOT-MUF-HPF on this one test
over 22 days.  This is a surprise to me as I thought both models started
off from the same base... IONCAP.  But they don't seem to unless my use
of Qe at zero is a wrong assumption in ICEPAC.

This may all be a fluke of one experiment but I am really surprised that
VOACAP, ICEPAC and Rec. 533 have such different values for the MUF on a
common path and solar conditions.  Also, the test data was collected on
a period with no major flares and the geomagnetic index was below storm
level on all days... i.e. a very quiet period.

Greg Hand may be able to shed more light on the FOT-MUF-HPF prediction
model in ICEPAC.  The VOACAP model is essentially the one used in ITSA-1
(1966) according to the authors of IONCAP.

I surely would like to get any comments from people who have been using
any of these three models.

George

Lane Consultant




------------------------------

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End of VOACAP Digest, Vol 5, Issue 2
************************************



--

73 de Tomas, NW7US (AAR0JA/AAA0WA)

: Propagation Editor for CQ, CQ VHF, and Popular Communications :
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